JP2002233138A - Switching power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate, in a switching power supply unit that automatically switches a switching power supply operation of a voltage-boosting type and that of a voltage step-down type using a single coil, a phenomenon in which both the switching power supply operations stop when switching is made between the voltage-boosting switching power supply operation and the voltage step-down switching power supply operation, and a phenomenon in which both the switching power supply operations simultaneously occur and the power conversion efficiency of the power supply is deteriorated. SOLUTION: The output voltage EO1 of an error amplifier 2 is compared with a specified voltage VR2 at a voltage boosting/step-down switching circuit 6 to generate an operation mode specifying signal SS. According to an operation mode specified by the operation mode specifying signal SS, a switching control logic circuit 8 causes either of the voltage step-down switching circuit 9 or the voltage-boosting switching circuit 10 to exclusively perform the switching operation. Therefore, the switching power supply operations are prevented from being both stopped or simultaneously taking place, when the switching is made between the voltage-boosting switching power supply operation and the voltage step-down switching power supply operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a step-up / step-down switching power supply for use in an electronic device or the like using a battery as a power source and for obtaining an output voltage higher or lower than a battery voltage.

[0002]

2. Description of the Related Art In recent years, in an electronic device using a battery as a power source, in order to operate with a small number of batteries and extend the life of a system battery, and to install the device on a set board and reduce the cost of a switching coil, A switching power supply device that is configured by using one switching coil and that switches between a step-down switching operation and a step-up switching operation automatically is used. Hereinafter, the above-described conventional switching power supply device will be described with reference to the drawings.

FIG. 11 is a circuit diagram of a conventional switching power supply device. This switching power supply includes a step-down switching circuit 9 for lowering a secondary power supply voltage VS from a voltage VI of a primary power supply 1 of an input voltage, and a primary power supply 1
A boosting switching circuit 10 for boosting the secondary-side power supply voltage VS from the voltage VI, and a coil L1 for accumulating and discharging energy connected to both ends of each of the step-down and boosting switching circuits 9, 10. Capacitor C1 for smoothing the switching output of each of the step-down and step-up switching circuits 9 and 10, and the voltage VS of the capacitor C1
(Secondary-side power supply voltage) is divided by a resistor and a reference voltage V
O, an error amplifier 2 that amplifies by comparing with O, a first triangular wave generating circuit 51, and a second triangular wave generating circuit 52 having an output in a voltage range different from that of the first triangular wave generating circuit 51.
And the output of the error amplifier 2 and the first triangular wave generation circuit 51
The comparator 53 drives the step-down switching circuit 9 based on the result of comparison with the output of the second triangular wave generation circuit 52, and the comparator 53 drives the step-down switching circuit 10 based on the result of comparing the output of the error amplifier 2 and the output of the second triangular wave generation circuit 52. 54
And

D1 and D2 are diodes, and Q1 and Q2 are N
A switching element composed of a channel MOS transistor, R1, R2, and R3 are resistors; VR1 is a variable resistor;
2 is a capacitor.

[0005] The pulse generation circuit 55 is configured such that the period of the rising edge of the triangular wave 1 output from the first triangular wave generating circuit 51 is L
A (low) level is output, and an H (high) level is output during the falling time of the triangular wave 1. The output of the comparator 54 is ANDed with the output of the pulse generation circuit 55 by the AND circuit 56, and is input to the gate of the boosting switching element Q2.

The first triangular wave generating circuit 51 and the second triangular wave generating circuit 52 determine whether the second triangular wave generating circuit 52 generates the triangular wave 2 based on the triangular wave 1 generated by the first triangular wave generating circuit 51. Alternatively, the triangular wave 1 of the first triangular wave generation circuit 51 is generated based on the triangular wave 2 generated by the second triangular wave generation circuit 52. The relationship between the triangular wave 1 and the triangular wave 2 is inverted with respect to a predetermined potential, and the triangular wave 2 is at a position higher in potential than the triangular wave 1. 12 and 13 show the relationship between the triangular wave 1 and the triangular wave 2. FIG. 12 is a diagram in a case where two triangular waves are set to have a mutually inverted relationship without overlapping. FIG.
FIG. 4 is a diagram when two triangular waves are set in an inverted relationship with each other in a situation where they overlap each other.

The output voltage EO of the error amplifier 2 changes depending on the relationship between the primary power supply voltage VI and the secondary power supply voltage VS due to the charge stored in the smoothing capacitor C1. When the primary power supply voltage VI is higher than the secondary power supply voltage VS, the output voltage EO of the error amplifier 2 has a low voltage value and is at the same level as the voltage range of the triangular wave 1. Switching element Q1
Performs a switching operation, and the system operates as a step-down switching power supply. At this time, the output of the comparator 54 becomes L level, and the boosting switching element Q2 does not operate. “(1) EO (at the time of step-down)” in FIGS. 12 and 13 indicates the output level of the output voltage EO of the error amplifier 2 in this situation. 12 and 13
SQ1 and SQ2 in “(1) Step-down” are step-down switching element Q1 and step-up switching element Q in this situation.
2 is a gate input, and indicates the timing of each switching operation. Each switching element Q1, Q
2 is ON when each gate input SQ1, SQ2 is at H level
(ON) Operates and conducts, OFF when L level
It operates and becomes non-conductive.

When the primary power supply voltage VI is equal to the secondary power supply voltage VS
If lower, the output voltage EO of the error amplifier 2 has a higher voltage value and is at the same level as the voltage range of the triangular wave 2,
By the output of the comparator 54, the boosting switching element Q2 performs a switching operation, and the system operates as a boosting switching power supply. At this time, the comparator 5
3 is at the H level, and the step-down switching element Q
1 is always conductive. “(3) EO (when boosted)” in FIG. 12 or “(4) EO (when boosted)” in FIG. 13 indicates the output level of the output voltage EO of the error amplifier 2 in this situation. SQ1 and SQ2 of "(3) When boosting" in FIG. 12 or "(4) When boosting" in FIG. 13 indicate the timing of the switching operation of the step-down switching element Q1 and the step-up switching element Q2 in this situation. . The difference between the H level timing of the gate input SQ2 of the boosting switching element Q2 and the output of the comparator 54 resulting from the comparison of the EO (at the time of boosting) and the triangular wave 2 by the comparator 54 is that the pulse generation circuit 5
This is because the output of No. 5 becomes the L output during the rising time of the triangular wave 1, and the output of the comparator 54 is cut off by the AND circuit 56 to become the gate voltage of the boosting switching element Q2. The pulse generating circuit 55 outputs H during the falling period of the triangular wave 1. The pulse generating circuit 55 is provided to limit the maximum duty of the boosting operation of the boosting switching element Q2 so that the coil L1 is not magnetically saturated during the operation of the boosting switching power supply.

In this conventional switching power supply, 1
According to the relationship between the secondary power supply voltage VI and the secondary power supply voltage VS, the voltage value of the output voltage EO of the error amplifier 2 changes and automatically switches between the step-down switching power supply operation and the step-up switching power supply operation. Has become.

[0010]

However, in the above-described conventional switching power supply, switching between the step-down switching power supply operation and the step-up switching power supply operation is performed by the output voltage EO of the error amplifier 2 and the voltages of the triangular waves 1 and 2. Since it is determined by the relationship, when the switching operation is switched from the step-down switching power supply operation to the step-up switching power supply operation or vice versa, one of the following two problems is very likely to occur. The first problem is that both the step-down switching power supply operation and the step-up switching power supply operation stop, and an uncontrolled state occurs. A second problem is that the step-down switching power supply operation and the step-up switching power supply operation occur simultaneously, and the power conversion efficiency of the power supply decreases.

The above will be described with reference to the drawings. FIG.
Is set so that the minimum value of the triangle wave 2 is higher than the maximum value of the triangle wave 1, and the triangle wave 1 and the triangle wave 2 do not overlap in terms of potential. The description of the step-down switching power supply operation and the step-up switching power supply operation is as described in the section of the prior art. The above-described first problem occurs when the operation is switched between the step-down switching power supply operation and the step-up switching power supply operation. At this time, the output voltage EO of the error amplifier 2 is at the position of “(2) EO (at the time of switching)” in FIG. Therefore, the gate voltages of the switching elements Q1 and Q2 are SQ1,
As shown by SQ2, when both the step-down switching operation and the step-up switching operation are stopped, the switching control operation to the secondary power supply is stopped. The step-down switching element Q1 is always on, and the step-up switching element Q2 is always off. In this case, the secondary power supply voltage VS passes through an element interposed between the primary power supply 1 and the secondary power supply, that is, the primary power supply voltage through the step-down switching element Q1, the coil L1, and the rectifying diode D2. Only the VI has been communicated. In a system in which the load of the load circuit 11 to which the secondary power supply voltage VS is supplied fluctuates, the load fluctuation is caused by the resistance component of the element interposed between the primary power supply 1 and the secondary power supply. , 2
The secondary power supply voltage VS will be changed. When another device other than the secondary-side power supply system is connected to the primary-side power supply 1 and the other device changes the primary-side power supply voltage VI, the secondary-side power supply voltage VS is similarly changed. Give fluctuation. That is, the change in the primary power supply voltage VI is directly transmitted to the secondary power supply voltage VS due to the non-control state,
Crosstalk from the other device to the secondary side power supply system will occur.

FIG. 13 shows a case where the maximum value of the triangular wave 1 is set to be higher than the minimum value of the triangular wave 2, and the triangular waves 1 and 2 overlap in terms of potential. In this case, the above-described second problem occurs when the operation is switched between the step-down switching power supply operation and the step-up switching power supply operation. The output voltage EO of the error amplifier 2 at this time
Is located at the position of “(2) EO (1 at the time of switching)” or “(3) EO (2 at the time of switching)” in FIG. 13, and is located in a range where the triangular waves 1 and 2 overlap with each other in potential.
Therefore, the gate voltages of the switching elements Q1 and Q2 are SQ1, SQ2,
Alternatively, as shown in SQ1 and SQ2 of "(3) When switching 2", the step-down switching power supply operation and the step-up switching power supply operation occur simultaneously, and the power supply from the primary power supply 1 to the secondary power supply is performed. The power conversion efficiency will be reduced. “(2) 1 at the time of switching” in FIG. 13 is the case where EO is potentially closer to the triangular wave 1, and the duty when SQ1 is L is larger than the duty when SQ2 is H. In “(3) at the time of switching 2” in FIG. 13, EO is potentially closer to the triangular wave 2 and when EO is at a higher voltage than this level, the duty when SQ2 is H is higher than the duty when SQ1 is L. growing.

If the relationship between the triangular wave 1 and the triangular wave 2 is appropriately set, the switching between the step-down switching power supply operation and the step-up switching power supply operation ideally seems to be performed appropriately. The existence of the above offset causes either the first or second problem described above. That is, the relationship between the triangular wave 1 and the triangular wave 2 is shown in FIG.
If the maximum value of the triangular wave 1 and the minimum value of the triangular wave 2 are set to be in the middle between the cases of FIG. 2 and FIG. 13, the step-down switching power supply operation and the step-up switching power supply operation are continuously switched, and However, in reality, there is offset variation on the circuit, and unless a special adjustment process is added, the configuration shown in FIG.
Thus, the relationship between the triangular wave 1 and the triangular wave 2 is established, and either the first or second problem described above occurs.

According to the present invention, there is provided a switching power supply device for automatically switching between a step-up switching power supply operation and a step-up switching power supply operation using one switching coil. It is possible to stably automatically switch between step-down switching power supply operation and step-up switching power supply operation without preventing two problems and without stopping the switching control of the secondary side power supply and without reducing the power conversion efficiency of the power supply. The purpose of the present invention is to provide a switching power supply that can be used.

[0015]

According to a first aspect of the present invention, there is provided a switching power supply, comprising:
Both ends are connected to a step-down switching circuit for stepping down a secondary power supply voltage, a step-up switching circuit for boosting a secondary power supply voltage from a primary side power supply voltage, and step-down and step-up switching circuits. , A capacitor that smoothes the switching output of each of the step-down and step-up switching circuits to generate a secondary power supply voltage, and an error amplifier that compares the secondary power supply voltage with a reference voltage and amplifies a difference voltage therebetween. And an inversion circuit that generates an inversion voltage obtained by inverting the output voltage of the error amplifier with reference to a predetermined voltage, and comparing the output voltage of the error amplifier with the predetermined voltage or the inversion voltage,
A step-up / step-down switching circuit that outputs the comparison result as an operation mode designating signal for designating an operation mode of the step-down switching power supply operation and the step-up switching power supply operation, and an output voltage of the error amplifier and an inversion circuit. A selection circuit that inputs an inversion voltage and outputs one of an output voltage and an inversion voltage of an error amplifier according to an operation mode specified by an operation mode specification signal; a triangular wave generation circuit that generates a triangular wave signal; A comparator that generates an original signal for the switching operation of the step-down switching circuit and the step-up switching circuit by comparing the output of the circuit with the triangular wave signal of the triangle wave generating circuit, and an operation mode designating signal and a comparator of the step-up / step-down switching circuit Input the generated switching operation original signal and the operation mode designating signal When the switching power supply operation mode is specified, the step-down switching circuit performs switching operation according to the original signal of the switching operation and stops the switching operation of the boost switching circuit, and the operation mode specification signal specifies the boost switching power supply operation mode A switching control logic circuit that causes the boosting switching circuit to perform a switching operation in accordance with an original signal of the switching operation and stops the switching operation of the step-down switching circuit.

According to a second aspect of the present invention, there is provided a switching power supply device for stepping down a secondary power supply voltage from a primary power supply voltage of an input voltage, and a secondary power supply from the primary power supply voltage. A step-up switching circuit for stepping up a voltage, a coil having both ends connected to each of a step-down type and a step-up type switching circuit, and smoothing the switching output of each of the step-down and step-up type switching circuits to reduce a secondary side power supply voltage. A generating capacitor, an error amplifier that compares a secondary power supply voltage with a reference voltage and amplifies the difference voltage, and an inverting circuit that generates an inverted voltage obtained by inverting an output voltage of the error amplifier with reference to a predetermined voltage. Comparing the primary power supply voltage with the secondary power supply voltage, and when the primary power supply voltage is higher than the secondary power supply voltage, comparing the inversion voltage generated by the inversion circuit with a predetermined voltage; Is output as an operation mode designating signal for designating the operation mode of the step-down switching power supply operation and the step-up switching power supply operation. When the primary-side power supply voltage is lower than the secondary-side power supply voltage, the error amplifier A step-up / step-down switching circuit for comparing an output voltage with a predetermined voltage and outputting a result of the comparison as an operation mode designating signal for designating an operation mode between a step-down switching power supply operation and a step-up switching power supply operation, and an error amplifier A selection circuit that inputs the output voltage of the error amplifier and the inversion voltage generated by the inversion circuit and outputs one of the output voltage and the inversion voltage of the error amplifier according to the operation mode specified by the operation mode specification signal; The signal is generated by comparing the output of the selection circuit with the triangular wave signal of the triangular wave generation circuit. For generating an original signal for the switching operation of the step-up switching circuit and the step-up switching circuit, an operation mode designation signal for the step-up / step-down switching circuit, and an original signal for the switching operation generated by the comparator, and an operation mode designation signal Specifies the step-down switching power supply operation mode, causes the step-down switching circuit to perform switching operation according to the original signal of the switching operation and stops the switching operation of the step-up switching circuit, and the operation mode designation signal indicates the step-up switching power supply operation mode. A switching control logic circuit that causes the step-up switching circuit to perform a switching operation in accordance with the original signal of the switching operation and stops the switching operation of the step-down switching circuit.

According to a third aspect of the present invention, there is provided a switching power supply device for stepping down a secondary power supply voltage from a primary power supply voltage of an input voltage, and a secondary power supply from the primary power supply voltage. A step-up switching circuit for stepping up a voltage, a coil having both ends connected to each of a step-down type and a step-up type switching circuit, and smoothing the switching output of each of the step-down and step-up type switching circuits to reduce a secondary side power supply voltage. A generating capacitor, an error amplifier that compares a secondary power supply voltage with a reference voltage and amplifies the difference voltage, a triangular wave generating circuit that generates a first triangular wave signal, and a first triangular wave generated by the triangular wave generating circuit An inverting circuit that generates a second triangular wave signal obtained by inverting the signal with reference to a predetermined voltage, compares the output voltage of the error amplifier with the predetermined voltage, and compares the comparison result with a step-down switch. Boost / step-down switching circuit for outputting an operation mode designating signal for designating an operation mode between a switching power supply operation and a boost switching power supply operation, and a first triangular wave signal generated by a triangular wave generating circuit and generated by an inverting circuit. A selection circuit that receives the second triangular wave signal and outputs one of the first triangular wave signal and the second triangular wave signal in accordance with the operation mode specified by the operation mode specifying signal; and an output voltage of the error amplifier. And a comparator that generates an original signal for the switching operation of the step-down switching circuit and the step-up switching circuit by comparing the output of the selection circuit with the output of the selection circuit. Input signal and the operation mode designation signal designates the step-down switching power supply operation mode Switching operation of the step-down switching circuit according to the original signal of the switching operation and stopping the switching operation of the step-up switching circuit, and switching the step-up switching circuit when the operation mode designation signal designates the step-up switching power supply operation mode. A switching control logic circuit that performs a switching operation according to an original signal of the operation and stops the switching operation of the step-down switching circuit.

According to the configuration of the present invention, the step-up / step-down switching circuit generates the operation mode designating signal, and the switching control logic circuit performs the step-down switching in accordance with the operation mode designated by the operation mode designating signal. One of the switching circuit and the step-up switching circuit is switched according to an original signal of the switching operation generated by the comparator, and the switching operation of the other switching circuit is stopped. As described above, only one of the step-down switching circuit and the step-up switching circuit always performs the switching operation in accordance with the operation mode specified by the operation mode specifying signal. When switching from switching power supply operation, both operations are stopped and switching control of the secondary power supply is stopped, and both operations occur at the same time and the power conversion efficiency of the power supply is not reduced, and the step-down type is stable. A switching power supply device that automatically switches between a switching power supply operation and a step-up switching power supply operation can be realized.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A feature of the present invention is that it is possible to automatically switch between a step-down switching power supply operation and a step-up switching power supply operation in accordance with the situation of the primary power supply voltage and the secondary power supply voltage. By using a switching power supply device including only one coil as in the following embodiments, when it is necessary to switch between a step-down switching power supply operation and a step-up switching power supply operation, Only one of the switching circuit and the step-up switching circuit always performs the switching operation, and when the switching power supply operation of the step-down type or the step-up type is switched, both of the above two switching circuits are stopped or both of them are stopped. That is, the configuration is such that no malfunction occurs.

FIG. 1 shows a first embodiment of the present invention.
FIG. 2 is a circuit diagram illustrating a configuration of a switching power supply device according to an embodiment. This switching power supply device, as in the conventional example shown in FIG.
A step-down switching circuit 9 for stepping down the secondary power supply voltage VS, a step-up switching circuit 10 for boosting the secondary power supply voltage VS from the voltage VI of the primary power supply 1,
A coil L1 that stores and releases energy connected to both ends of each of the step-down and step-up switching circuits 9, 10
An electrolytic capacitor C1 for smoothing the switching output of each of the step-down and step-up switching circuits 9 and 10; a voltage obtained by dividing the voltage VS (secondary power supply voltage) of the capacitor C1 by resistance; VO and an error amplifier 2 that amplifies the difference voltage. Further, similarly to the conventional example, the step-down switching circuit 9 includes a diode D1.
And a switching element Q1 of an N-channel MOS transistor. The boosting switching circuit 10 includes a diode D2 and a switching element Q2 of an N-channel MOS transistor. R1 and R2 and a variable resistor VR
1, a capacitor C2 and a resistor R3 are connected between the output terminal of the error amplifier 2 and the (-) input terminal. The load circuit 11 is configured by an electronic circuit of an electronic device set.

In addition, in the present embodiment, the triangular wave generation circuit 4 directly connected to the plus (+) input terminal of the comparator 7, the control signal switching circuit 5, the step-down switching power supply operation and the step-up switching power supply A step-up / step-down switching circuit 6 for outputting an operation mode designating signal SS for designating one of the operation modes; a comparator 7 for generating an original signal for the switching operation of the step-down switching circuit 9 and the step-up switching circuit 10; , Connected between the output stage of the comparator 7 and the step-down switching circuit 9 and the step-up switching circuit 10 to convert the original signal of the switching operation of the comparator 7 to the step-down type in accordance with the operation mode designated by the operation mode designation signal SS. Switching to be transmitted by switching to the switching circuit 9 or the step-up switching circuit 10 And a control logic circuit 8.

The primary power supply voltage VI is variable because it is assumed that a battery is used as the primary power supply 1. The secondary power supply voltage VS does not depend on the primary power supply voltage VI, and is controlled by this switching power supply device so as to be always a constant voltage. For example, when the primary power supply voltage VI is smaller than the secondary power supply voltage VS, the switching control logic circuit 8
Stops the operation of the step-down switching circuit 9 and operates the step-up switching circuit 10 to control the secondary power supply voltage VS to a constant voltage. At this time, the boosting switching element Q2 performs a switching operation to control the secondary power supply voltage VS. Step-down switching element Q1 is ON
In the operating state, the primary power supply voltage VS and the current of the primary power supply are supplied to the coil L1 through Q1. The smoothing capacitor C1 smoothes the switching output of each of the step-down switching circuit 9 and the step-up switching circuit 10 to generate the secondary power supply voltage VS. The load circuit 11 is a load of the secondary power supply and is usually an electronic circuit of an electronic device set. It is assumed that this load current is not always constant and changes according to the status of the electronic device set.

The error amplifier 2 compares the voltage obtained by dividing the secondary power supply voltage VS by the resistors R1, R2, and VR1 with a reference voltage VO to output an output voltage EO1. The resistor R3 and the capacitor C2 set the gain and frequency characteristics of the error amplifier 2. Adjust the values of R3 and C2 to maintain the stability of the negative feedback control loop of the switching power supply. The (−) input terminal of the error amplifier 2 is a feedback point of a negative feedback control loop of the switching power supply. The negative feedback control loop changes the (−) input terminal voltage of the error amplifier 2, that is, the secondary power supply voltage VS to R1. , R
2. The voltage divided by VR1 is the (+) input terminal voltage of the error amplifier 2, that is, the reference voltage V of the reference voltage source 3.
It becomes equal to O. The reference voltage source 3 is a very stable voltage source composed of a constant voltage electronic circuit. As a result, the secondary power supply voltage VS is stable by multiplying the reference voltage VO by the inverse proportional constant of the resistance division of R1, R2 and VR1. Thus, the voltage becomes a constant controlled voltage. The output voltage EO1 of the error amplifier 2 is output to the control signal switching circuit 5 and the step-up / step-down switching circuit 6.

Here, the output voltage EO1 of the error amplifier 2
Consider the movement of the voltage value of. Assuming that the operation of the switching power supply is always constant, that is, the operation is fixed to either the step-down switching power supply operation or the step-up switching power supply operation, and the switching operation is performed with a constant PWM (pulse width modulation) duty. When the primary power supply voltage VI is high, the secondary power supply voltage VS also increases.
O1 moves in the direction in which the voltage value decreases. When the primary power supply voltage VI is low, the secondary power supply voltage VS is also low, so that the error amplifier output voltage EO1 moves in the direction of increasing the voltage value. The secondary power supply voltage VS is connected to the (-) input terminal of the error amplifier 2 through the resistance division, and the output voltage EO1 is output in the form of an inverting amplifier.
O1 moves.

The triangular wave generating circuit 4 is a signal generating circuit necessary for causing the switching power supply device to perform a switching operation, and generates a signal having a triangular wave-shaped potential characteristic over time. This signal is called a triangular wave. The triangular wave generated here is input to the (+) input terminal of the comparator 7.

The step-up / step-down switching circuit 6 compares the output voltage EO1 of the error amplifier 2 with the predetermined voltage VR2 of the voltage source 13, and, based on the comparison result, operates the step-down switching power supply or the step-up switching power supply. An operation mode designating signal SS for determining whether or not the operation mode is selected is output. Here, for example, the error amplifier output voltage EO1 is set to a predetermined voltage V
When lower than R2, the L-level operation mode designating signal SS
Is output to operate the step-down switching power supply. When the error amplifier output voltage EO1 is higher than the predetermined voltage VR2, an H-level operation mode designating signal SS is output to operate the step-up switching power supply. . The operation mode designating signal S at the time of the step-down switching power supply operation and the step-up switching power supply operation
The level of S may be opposite to the above depending on the configuration of the selection circuit 14 and the switching control logic circuit 8.

The control signal switching circuit 5 outputs the voltage EO1 obtained by inverting the input output voltage EO1 of the error amplifier 2 using the resistors R4 and R5 with reference to the predetermined voltage VR2 of the voltage source 13. And a selection circuit for selecting and outputting either the output voltage EO1 of the error amplifier 2 or the output voltage EO2 of the error amplifier 12 in accordance with the operation mode designated by the operation mode designation signal SS of the step-up / step-down switching circuit 6. 14 is provided. here,
Selection circuit 14 when operation mode designating signal SS is at L level
Outputs the voltage EO2 to the (-) input terminal of the comparator 7, and the selection circuit 14 outputs the voltage EO1 to the (-) input terminal of the comparator 7 when the operation mode designation signal SS is at the H level. Error amplifier 12 and resistor R
4, R5 and the voltage source 13 constitute an inverting circuit. The resistance values of the resistors R4 and R5 are the same.

The comparator 7 is a switching element for causing a switching operation of the switching power supply device, and compares the output voltage EO1 or EO2 of the control signal switching circuit 5 with the triangular wave from the triangular wave generating circuit 4 in terms of voltage. , PWM (pulse width modulation) switching output signal SC.

The switching control logic circuit 8 is located between the comparator 7 and two switching circuits, ie, the step-down switching circuit 9 and the step-up switching circuit 10, and boosts / decreases the PWM switching output signal SC output from the comparator 7. Depending on the operation mode designating signal SS output from the step-down switching circuit 6, the step-down switching circuit 9 or the step-up switching circuit 1
0, the operation of the step-up switching circuit 10 is stopped and the step-down switching circuit 9
Or the switching operation of the step-up switching circuit 10 while the switching element Q1 of the step-down switching circuit 9 is ON. Specifically, it is configured in the same manner as, for example, a switching control logic circuit 8 in FIG. 2 described later.

Hereinafter, the switching power supply operation in the above configuration will be described in detail. The relationship between the triangular wave, VR2, EO1, and EO2 is as shown in FIGS. 7A and 7B. FIG. 7A shows a state in which the primary side power supply voltage VI is higher than the secondary side power supply voltage VS during the step-down switching power supply operation.
FIG. 7B shows the relationship between the triangular wave, VR2, EO1, and EO2 during the step-up switching power supply operation in which the primary power supply voltage VI is lower than the secondary power supply voltage VS.

The relationship between the triangular wave and VR2 is shown in FIG.
As shown in (b), the voltage value of VR2 is set to be slightly higher than the minimum voltage value of the triangular wave. This is to prevent the voltage value of VR2 from being lower than the minimum voltage value of the triangular wave due to the offset variation on the circuit. If it can be realized by a circuit having no offset variation, the minimum voltage value of the triangular wave and the voltage of VR2 can be realized. The values may be the same. EO
2 is a voltage obtained by inverting EO1 by the error amplifier 12 with reference to VR2.

In the case of the step-down switching operation shown in FIG. 7A, EO1 is lower than VR2, and EO2 is lower than V2.
The voltage becomes higher than R2. EO1 and VR2 are compared by the step-up / step-down switching circuit 6, and as a result, EO1 becomes VR
When the voltage is lower than 2, EO2 is input to the (-) input terminal of the comparator 7, and the selection circuit 14 is operated by the operation mode designation signal SS so that EO1 is not input. The comparator 7 compares EO2 with the triangular wave, and as a result, the output SC of the comparator 7 has a switching waveform as shown in FIG. The step-up / step-down switching circuit 6 controls the switching control logic circuit 8, and the outputs SQ1 and SQ2 of the switching control logic circuit 8 are as shown in FIG. Here, the switching operation of the step-up switching element Q2 is stopped, the switching control of the step-down switching element Q1 is performed, and the switching operation is performed so that the secondary power supply voltage VS is reduced with respect to the primary power supply voltage VI. When the primary side power supply voltage VI increases, EO1 decreases and EO2 increases as described above. EO
1 and EO2 move from the position (1) to the position (2) in FIG. As a result, the output SC of the comparator 7 and the gate input SQ1 of the step-down switching element Q1 become L
Even when the level time becomes longer and the primary power supply voltage VI rises, control is performed so that the secondary power supply voltage VS becomes constant.

In the case of the step-up switching operation shown in FIG. 7B, EO1 becomes higher than VR2, and EO2 becomes higher than V2.
The voltage becomes lower than R2. EO1 and VR2 are compared by the step-up / step-down switching circuit 6, and as a result, EO1 becomes VR
When the voltage is higher than 2, EO1 is input to the (-) input terminal of the comparator 7, and the selection circuit 14 is operated by the operation mode designation signal SS so that EO2 is not input. The comparator 7 compares EO1 with the triangular wave, and the output SC of the comparator 7 has a switching waveform as shown in FIG. The step-up / step-down switching circuit 6 controls the switching control logic circuit 8, and the outputs SQ1 and SQ2 of the switching control logic circuit 8 are as shown in FIG. Here, the switching operation of the step-down switching element Q1 is stopped, the step-down switching element Q1 is controlled to be always turned on, the switching control of the step-up switching element Q2 is performed, and the primary-side power supply voltage VI is reduced by 2%. The switching operation is performed so that the secondary power supply voltage VS is boosted. When the primary power supply voltage VI decreases, EO1 increases as described above, and EO2 decreases. EO1, E
O2 moves from the position (1) to the position (2) in FIG. 7B. As a result, the time when the output SC of the comparator 7 is at the L level and the gate input SQ2 of the boosting switching element Q2 is at the H level becomes longer, and the secondary power supply voltage VS becomes constant even if the primary power supply voltage VI drops. Control will be applied.

EO1 and VR in the step-up / step-down switching circuit 6
2 is compared with the operation mode designating signal SS.
Thus, the switching between the step-down switching power supply operation and the step-up switching power supply operation is automatically switched according to the change in the primary-side power supply voltage VI.

As described above, according to the present embodiment, in the switching power supply device that automatically switches between the step-down and step-up switching power supply operations using only one coil L1 as the switching coil, the step-up / step-down switching circuit 6 And the output voltage EO1 of the error amplifier 2 and the predetermined voltage V
The switching control logic circuit 8 generates an operation mode designating signal SS by comparing the operation mode signal R2 with the switching control logic circuit 8 according to the operation mode designated by the operation mode designating signal SS.
Step-down switching circuit 9 and step-up switching circuit 1
0, the switching operation of the secondary power supply is stopped when switching between the step-down switching power supply operation and the step-up switching power supply operation, and the power conversion efficiency of the power supply is also reduced. It is possible to realize a switching power supply operation that automatically switches between a step-down switching power supply operation and a step-up switching power supply operation without being dropped.

In the configuration shown in FIG. 1, the output voltage EO1 of the error amplifier 2 is compared with the predetermined voltage VR2 by the step-up / step-down switching circuit 6. In this case, the step-up / step-down switching circuit 6 , The voltage EO1 is input to the plus (+) input terminal of the comparator, the predetermined voltage VR2 is input to the minus (−) input terminal, and the output signal is used as the operation mode designation signal SS.

It should be noted that instead of inputting the output voltage EO1 of the error amplifier 2 to the step-up / step-down switching circuit 6, the output voltage EO2 of the error amplifier 12 is input (indicated by a dotted arrow A in FIG. 1), Similar effects can be obtained by comparing EO2 with predetermined voltage VR2 and outputting operation mode designating signal SS. In this case, when the voltage EO2 is higher than the predetermined voltage VR2, an L-level operation mode designating signal SS is output to perform the step-down switching power supply operation. When the voltage EO2 is lower than the predetermined voltage VR2, the H-level operation is performed. The mode designating signal SS is output to operate the step-up switching power supply. For example, a comparator is used as the step-up / step-down switching circuit 6, a predetermined voltage VR2 is input to the plus (+) input terminal of the comparator, and the voltage EO is input to the minus (-) input terminal.
2 and inputs the output signal as an operation mode designating signal SS.

In FIG. 1, when EO1 = VR2, the step-up / step-down switching circuit 6 determines which of the H level and the L level is to be output as the operation mode designating signal SS depending on the offset in the circuit. Since the DC gain of the error amplifier 2 at the preceding stage is infinite, this offset does not affect the switching between the step-up / step-down. Further, the step-up / step-down switching circuit 6 is connected to EO2 and VR2.
When EO2 = VR2, which of the H level and the L level is output as the operation mode designating signal SS is determined by an offset in the circuit. Error amplifier 2 DC
Since the gain is infinite, there is no effect on switching between step-up and step-down.

[Second Embodiment] FIG. 2 shows a second embodiment of the present invention.
FIG. 2 is a circuit diagram illustrating a configuration of a switching power supply device according to an embodiment. 2, components corresponding to those in FIG. 1 are denoted by the same reference numerals, and description of the same components is omitted.

In this embodiment, the step-up / step-down switching circuit 6 is different from that of FIG. 1 in that the output voltage EO1 of the error amplifier 2 and the output voltage EO2 of the error amplifier 12 are input to the step-up / step-down switching circuit 6. And then
The primary power supply voltage VI and the secondary power supply voltage VS are input. Other configurations are the same as those in FIG.

In this embodiment, a specific configuration example of the switching control logic circuit 8 is shown, and the switching control logic circuit 8 is connected to the NOR circuits 25, 26, 2
7, 28, OR circuits 29, 30 and inverters 31, 3
2, 33, and 34. Here, the switching control logic circuit 8 is connected to a start control signal source 23 and a start drive signal source 24.

The start-up control signal source 23 and the start-up drive signal source 24 are operated by the switching power supply control circuit irrespective of the step-down switching power supply operation and the step-up switching power supply operation described directly in the present invention. This is a signal source used when raising the secondary power supply voltage VS in a situation where there is no power supply. Basically, the power supply voltage of the switching power supply control circuit uses the secondary power supply voltage VS. In this case, if the secondary power supply voltage VS is a zero voltage or a non-zero voltage but a low voltage that is inappropriate for circuit operation, the switching power supply control circuit may not operate or may operate incorrectly even if it operates.

The activation control signal of the activation control signal source 23 is H
At the time of the level, the switching control logic circuit 8 stops the switching power supply control. That is, the output of the comparator 7 is not transmitted to the step-down switching circuit 9 and the step-up switching circuit 10. Instead, the step-up type switching circuit 1 is driven by the pulse output of the starting drive signal source 24.
The switching element Q2 of 0 is switched.
At this time, the gate voltage of the switching element Q1 of the step-down switching circuit 9 is always at the H level, the switching element Q1 is turned on, and the voltage and current from the primary power supply 1 are transmitted to the coil L1.

As described above, even in the case of the secondary power supply voltage VS at which the switching power supply control circuit cannot operate, the boosting switching circuit 10 is operated using the start-up control signal and the start-up drive signal, and It is possible to sufficiently raise the power supply voltage VS to a voltage at which the switching power supply control circuit operates. When the activation control signal of the activation control signal source 23 is set to L level after the secondary power supply voltage VS rises, the switching control logic circuit 8 operates as a switching power supply control circuit composed of the comparator 7 and the like at the preceding stage of this circuit. The signal is passed, and the switching control operates normally.

The step-up / step-down switching circuit 6 according to the present embodiment includes comparators 15, 16, and 17 and a two-input multiplexer circuit 18 including an inverter 19 and NOR circuits 20, 21, and 22. The comparator 15 compares the primary-side power supply voltage VI with the secondary-side power supply voltage VS, and switches the two-input multiplexer circuit 18 based on the output. Two inputs of the two-input multiplexer circuit 18 are connected to the output of the comparator 16 and the output of the comparator 17, respectively. Two-input multiplexer circuit 18
Selects one of the output signal of the comparator 16 and the output signal of the comparator 17 based on the output of the comparator 15 and outputs the selected signal. The output of the two-input multiplexer circuit 18 is input to the selection circuit 14 and the switching control logic circuit 8 as the output signal SS of the step-up / step-down switching circuit 6. The comparator 16 compares the output voltage EO2 of the error amplifier 12 with a predetermined voltage VR2,
The comparator 17 compares the output voltage EO1 of the error amplifier 2 with a predetermined voltage VR2.

In the step-up / step-down switching circuit 6, when the primary power supply voltage VI is higher than the secondary power supply voltage VS, the output of the comparator 15 becomes L level, and the two-input multiplexer circuit 18 selects the output of the comparator 16. Then, it is output as an output signal SS of the step-up / step-down switching circuit 6. That is, the result of comparing EO2 and VR2 by the comparator 16 becomes the output signal (switching signal) SS of the step-up / step-down switching circuit 6. In this case, when EO2 is higher than VR2, the output of the comparator 16 is at L level, and the operation mode designating signal SS is also at L level. When EO2 is lower than VR2, the output of the comparator 16 is at H level, and the operation mode designating signal SS is also at H level.

When the primary power supply voltage VI is lower than the secondary power supply voltage VS, the output of the comparator 15 becomes H level, and the two-input multiplexer circuit 18 selects the output of the comparator 17 to increase / decrease the voltage. 6 as an output signal SS. That is, EO
1 and VR2 result in a step-up / step-down switching circuit 6
Output. In this case, when EO1 is higher than VR2, the output of the comparator 17 is at H level, and the operation mode designation signal SS is also at H level. When EO1 is lower than VR2, the output of the comparator 17 is at L level, and the operation mode designating signal SS is also at L level.

The selection circuit 14 selects EO1 when the operation mode designating signal SS output from the two-input multiplexer circuit 18 is at H level, and selects EO2 when it is at L level.
Is output as an error signal input to the (−) input terminal of the comparator 7.

In the comparator 7, as in the case of FIG.
By comparing EO1 or EO2 selected by the selection circuit 14 with the triangular wave from the triangular wave generating circuit 4 in terms of voltage,
It outputs a PWM switching output signal SC to the switching control logic circuit 8.

In the switching control logic circuit 8, when the operation mode designating signal SS is at the H level, the signal SQ1 output to the gate of the step-down switching element Q1 is always at the H level regardless of the output signal SC of the comparator 7, and The signal SQ2 output to the gate of the switching element Q2 is a signal of a voltage level obtained by inverting the output signal SC of the comparator 7. That is, when the operation mode designating signal SS from the step-up / step-down switching circuit 6 is at the H level, the step-up switching power supply operates.

In the switching control logic circuit 8, when the operation mode designating signal SS is at L level, the signal SQ2 output to the gate of the boosting switching element Q2 is always at L level regardless of the output signal SC of the comparator 7, The signal SQ1 output to the gate of the step-down switching element Q1 is a signal of the same level as the output signal SC of the comparator 7. That is, when the operation mode designating signal SS from the step-up / step-down switching circuit 6 is at L level, the step-down switching power supply operates.

Here, FIG. 8A shows the primary power supply voltage VI.
FIG. 4 is a timing chart showing a switching operation when is larger than the secondary-side power supply voltage VS. Primary power supply voltage VI is 2
When the voltage is higher than the secondary power supply voltage VS, the output of the comparator 16 (comparison result between EO2 and VR2) is output from the two-input multiplexer circuit 18 in the step-up / step-down switching circuit 6.
Is selected as the operation mode designation signal SS. "(1)
EO2> VR2 ", the output signal SC of the comparator 7 when the output of the comparator 16 and the operation mode designating signal SS are at L level, the gate input signal SQ1 of the step-down switching element Q1, and the gate input signal SQ2 of the step-up switching element Q2. At this time, a step-down switching power supply operation is performed. In addition, when “(2) EO2 <VR2”, the output signal S of the comparator 7 when the output of the comparator 16 and the operation mode designating signal SS are at H level.
C, the gate input signal SQ of the step-down switching element Q1
1, the gate input signal SQ of the boosting switching element Q2
2 at this time, and the operation is a step-up switching power supply operation.

FIG. 8B is a timing chart showing a switching operation when the primary power supply voltage VI is smaller than the secondary power supply voltage VS. When the primary power supply voltage VI is smaller than the secondary power supply voltage VS, the output (comparison result of EO1 and VR2) of the comparator 17 is selected by the two-input multiplexer circuit 18 in the step-up / step-down switching circuit 6, and the operation mode is designated. It becomes signal SS. "(1) E
In the case of “O1> VR2”, the output signal SC of the comparator 7 when the output of the comparator 17 and the operation mode designating signal SS are at the H level, the gate input signal SQ1 of the step-down switching element Q1, and the gate input signal SQ2 of the step-up switching element Q2 , And at this time, the operation is the step-up switching power supply operation. When “(2) EO1 <VR2”, the output signal S of the comparator 7 when the output of the comparator 17 and the operation mode designating signal SS are at L level.
C, the gate input signal SQ of the step-down switching element Q1
1, the gate input signal SQ of the boosting switching element Q2
2 at this time, and a step-down switching power supply operation is performed.

As described above, according to the present embodiment, the primary side power supply voltages VI and 2
Depending on the potential relationship of the secondary power supply voltage VS, the error amplifier 2
The comparison result between the output voltage EO1 of the error amplifier 12 and the predetermined voltage VR2 or the output voltage EO2 of the error amplifier 12 and the predetermined voltage VR2
The operation mode designating signal SS is generated by selecting one of the comparison results with the operation mode designating signal SS.
The switching control logic circuit 8 always causes only one of the step-down switching circuit 9 and the step-up switching circuit 10 to perform the switching operation in accordance with the operation mode designated by the step (1). When switching between the switching power supply operation, the switching control of the secondary power supply does not stop and the power conversion efficiency of the power supply does not decrease, and the buck switching power supply operation and the boost switching power supply operation are automatically performed stably. Switching power supply operation can be realized.

In FIG. 2, the switching control logic circuit 8 is constituted by a NOR circuit, an OR circuit and an inverter as an example, but is constituted by using an AND circuit, a NAND circuit and an inverter. Is also good. The switching control logic circuit 8 in FIG. 1 can be similarly configured.

As shown in FIG. 3, in the step-down switching circuit 9, an inverter 41 and an N-channel MOS transistor Q3 are used instead of the diode D1 (FIG. 2).
In the boosting switching circuit 10, a synchronous rectification type switching power supply circuit may be provided by replacing the diode D2 (FIG. 2) with the inverter 42 and the N-channel MOS transistor Q4. All other configurations and circuit operations are the same as those in FIG.
Note that, also in the configuration of FIG. 1, the step-down switching circuit 9 and the step-up switching circuit 10 may be replaced with those of FIG.

In FIG. 2 and FIG. 3, when VI = VS, which of the H level and the L level is output is determined by the offset of the comparator 15. Further, when EO1 = VR2, the comparator 17 determines which of the H level and the L level is output by the offset of the comparator 17, but the amount of this offset is infinite when the DC gain of the error amplifier 2 at the preceding stage is infinite. There is no effect on switching between step-up and step-down. When EO2 = VR2, the comparator 16 determines whether to output the H level or the L level by the offset of the comparator 16, but this offset amount is infinite when the DC gain of the error amplifier 2 at the preceding stage is infinite. There is no effect on switching between step-up and step-down.

[Third Embodiment] FIG. 4 shows a third embodiment of the present invention.
FIG. 2 is a circuit diagram illustrating a configuration of a switching power supply device according to an embodiment. In FIG. 4, components corresponding to those in FIG. 1 are denoted by the same reference numerals. Further, a primary side power supply 1, a step-down switching circuit 9, a step-up switching circuit 10, a load circuit 11,
The smoothing capacitor C1, the error amplifier 2, the reference voltage source 3, the capacitor C2, the resistors R1, R2, R3 and the variable resistor VR1 are the same as those in FIG.

In the present embodiment, the output EO of the error amplifier 2 is directly connected to the (-) input terminal of the comparator 7,
The control signal switching circuit 5 is connected between a triangular wave generating circuit 4 for generating an original triangular wave signal necessary for the comparator 7 to perform a switching operation, and a (+) input terminal of the comparator 7.

The step-up / step-down switching circuit 6 according to the present embodiment compares the predetermined voltage VR2 of the voltage source 36 with the output voltage EO of the error amplifier 2 and outputs the comparison result as an operation mode designating signal SS. It consists of. Hereinafter, the step-up / step-down switching circuit 6 is referred to as a switching comparator 6.

The control signal switching circuit 5 in the present embodiment outputs a triangular wave 2 obtained by inverting a triangular wave 1 output from the triangular wave generating circuit 4 with reference to a predetermined voltage VR2 of a voltage source 36 by using resistors R4 and R5. An inverting amplifier 35,
There is provided a selection circuit 37 for selecting either the triangular wave 1 or the triangular wave 2 according to the operation mode specified by the operation mode specifying signal SS of the switching comparator 6 and outputting the selected signal to the (+) input terminal of the comparator 7. Here, the selection circuit 37 outputs the triangular wave 1 to the (+) input terminal of the comparator 7 when the operation mode designation signal SS is at the H level, and the selection circuit 37 outputs the triangle wave 2 to the comparator 7 when the operation mode designation signal SS is at the L level. 7 (+) input terminal. The inverting amplifier 35, the resistors R4 and R5, and the voltage source 36 constitute an inverting circuit. The resistance values of the resistors R4 and R5 are the same. The resistors R4 and R5 in FIG.
And the voltage value of the predetermined voltage VR2 are substantially the same as those in FIGS. 1 and 2, but need not be the same value.

Here, the behavior of the voltage value of the output voltage EO of the error amplifier 2 will be considered. Assuming that the operation of the switching power supply is always constant, that is, the operation is fixed to either the step-down switching power supply operation or the step-up switching power supply operation, and the switching operation is performed with a constant PWM (pulse width modulation) duty. When the primary power supply voltage VI is high, the secondary power supply voltage VS also increases, so that the error amplifier output voltage EO
Moves in the direction in which the voltage value decreases. Also, the primary side power supply voltage V
When I is low, the secondary-side power supply voltage VS also decreases, so that the error amplifier output voltage EO moves in a direction in which the voltage value increases. 2
The secondary power supply voltage VS is connected to the (−) input terminal of the error amplifier 2 through the resistance division, and the output voltage EO is output in an inverted amplifier format.

Hereinafter, the switching power supply operation in the above configuration will be described in detail. Triangle wave 1, triangle wave 2, and VR
The relationship between 2 and EO is as shown in FIGS. 9A and 9B. FIG. 9A shows a state in which the primary-side power supply voltage VI is higher than the secondary-side power supply voltage VS during the step-down switching power supply operation.
FIG. 9B shows the relationship among the triangular wave 1, the triangular wave 2, VR2, and EO during the step-up switching power supply operation in which the primary power supply voltage VI is lower than the secondary power supply voltage VS.

The relationship between the triangular waves 1, 2 and VR2 is shown in FIG.
As shown in (a) and (b), the reference voltage VR2 of the inverting amplifier 35 is set to be slightly lower than the maximum voltage value of the triangular wave 1 and slightly higher than the minimum voltage value of the triangular wave 2.
The triangular wave 1 and the triangular wave 2 are set so as to overlap each other around VR2. The reason for this setting is to prevent the triangular wave 1 and the triangular wave 2 from overlapping due to offset variations on the circuit. If the present system can be realized by a circuit having no offset variation, the maximum voltage value of the triangular wave 1 and the minimum voltage value of the triangular wave 2 may be set to be equal to VR2.

As described above, when the primary power supply voltage VI is 2
When the primary power supply voltage VS is higher than the secondary power supply voltage VS, the output voltage EO of the error amplifier 2 becomes lower.
O moves to a high voltage.

In the case of the step-down switching operation shown in FIG. 9A, EO moves as the primary power supply voltage VI changes.
When EO is lower than the predetermined voltage VR2, the switching comparator 6 outputs an H-level operation mode designating signal SS. As a result, the selection circuit 37 selects the triangular wave 1 and
The triangular wave 1 is input to the (+) input terminal of the comparator 7, and the triangular wave 2 is not input. In FIG. 9A, the triangular wave 1 is indicated by a solid line and the triangular wave 2 is indicated by a dotted line, which means that the triangular wave 1 is input to the (+) input terminal of the comparator 7. The comparator 7 compares EO with the triangular wave 1, and the output signal SC of the comparator 7 has a switching waveform as shown in FIG. The switching comparator 6 controls the switching control logic circuit 8, and the outputs SQ1 and SQ2 of the switching control logic circuit 8
(A). Here, the switching operation of the step-up switching element Q2 is stopped, the switching of the step-down switching element Q1 is controlled, and the primary side power supply voltage V
The switching operation is performed such that the secondary power supply voltage VS drops with respect to I. When the primary power supply voltage VI increases, EO decreases as described above. EO is (1) in FIG.
From (2) to (2). As a result, the time of the H level of the output SC of the comparator 7 and the L level of the gate input SQ1 of the step-down switching element Q1 become longer,
Control is performed so that the secondary power supply voltage VS becomes constant even if the primary power supply voltage VI increases.

In the case of the step-up switching operation shown in FIG. 9B, when the primary power supply voltage VI decreases, EO increases with the change, and when EO becomes higher than the predetermined voltage VR2, the switching is performed. The operation mode designating signal SS output from the comparator 6 becomes L level. As a result, the selection circuit 37 selects the triangular wave 2, and the triangular wave 2 is input to the (+) input terminal of the comparator 7, and the triangular wave 1 is not input. In FIG. 9B, the triangular wave 2 is indicated by a solid line and the triangular wave 1 is indicated by a dotted line, which means that the triangular wave 2 is input to the (+) input terminal of the comparator 7. The comparator 7 compares EO with the triangular wave 2, and the output signal SC of the comparator 7 has a switching waveform as shown in FIG.
The switching comparator 6 controls the switching control logic circuit 8, and the outputs SQ1 and SQ2 of the switching control logic circuit 8 are as shown in FIG. here,
The switching operation of the step-down switching element Q1 is stopped, the step-down switching element Q1 is controlled to be always turned on, the switching control of the step-up switching element Q2 is performed, and the secondary-side power supply is controlled with respect to the primary-side power supply voltage VI. The switching operation is performed so that the voltage VS increases. When the primary power supply voltage VI decreases, EO increases as described above. The EO moves from the position (1) to the position (2) in FIG. As a result, the time of the L level of the output SC of the comparator 7 and the H level of the gate input SQ2 of the boosting switching element Q2 become longer, and the secondary power supply voltage VS becomes constant even if the primary power supply voltage VI decreases. Control will be applied.

As described above, the switching comparator 6 compares the potential relationship between EO and VR2, whereby the operation of the step-down switching power supply and the operation of the step-up switching power supply are automatically performed due to the change in the primary power supply voltage VI. Switch.

FIG. 5 shows a specific configuration example of the switching control logic circuit 8 in the present embodiment. The switching control logic circuit 8 in FIG. 5 has a configuration in which two inverters 38 and 39 are added to the switching control logic circuit 8 in FIG. The start control signal source 23 and the start drive signal source 24 are the same as those in FIG. 2, and the description thereof will be omitted.

In the switching control logic circuit 8 in FIG. 5, when the operation mode designating signal SS is at H level, the signal SQ2 output to the gate of the boosting switching element Q2 is always at L level regardless of the output signal SC of the comparator 7. The signal SQ1 output to the gate of the step-down switching element Q1 is output from the output signal S
It is assumed that the signal has a voltage level inverted by C. That is, the operation mode designating signal SS from the switching comparator 6 becomes H
At the level, the step-down switching power supply operates.

In the switching control logic circuit 8, when the operation mode designating signal SS is at L level, the signal SQ output to the gate of the step-down switching element Q1 is output.
1 is always H regardless of the output signal SC of the comparator 7.
The signal SQ2 output to the gate of the boosting switching element Q2 is a signal of a voltage level obtained by inverting the output signal SC of the comparator 7. That is, when the operation mode designating signal SS from the switching comparator 6 is at the L level, a boost switching power supply operation is performed.

As described above, according to the present embodiment, the switching comparator 6 compares the output voltage EO of the error amplifier 2 with the predetermined voltage VR2 to generate the operation mode designating signal SS. In accordance with the operation mode designated by SS, the switching control logic circuit 8 always performs only one of the step-down switching circuit 9 and the step-up switching circuit 10 to perform the switching operation. When switching between the switching power supply operation and the switching power supply operation, the switching control of the secondary power supply does not stop and the power conversion efficiency of the power supply does not decrease. Switching power supply operation can be realized.

In the present embodiment, the triangular wave generating circuit 4 generates the triangular wave 1 shown in FIGS. 9A and 9B, but the triangular wave generating circuit 4 generates the triangular wave 1 shown in FIGS.
The triangular wave 2 shown in FIG.
May be configured to output a triangular wave 1.

Note that the switching comparator 6 sets EO =
In the case of VR2, which of the H level and the L level is output as the operation mode designating signal SS is determined by the offset of the switching comparator 6, and the amount of this offset is such that the DC gain of the error amplifier 2 in the preceding stage is infinite. Therefore, there is no influence on switching between step-up / step-down.

In FIGS. 4 and 5, the switching control logic circuit 8 is constituted by a NOR circuit, an OR circuit, and an inverter as an example.
The circuit may be configured using an ND circuit and an inverter.

As shown in FIG. 6, in the step-down switching circuit 9, the inverter 41 and the N-channel MOS transistor Q3 are substituted for the diode D1 (FIGS. 4 and 5). Instead of D2 (FIGS. 4 and 5), the inverter 42 and the N-channel MOS transistor Q4 may be replaced with a synchronous rectification type switching power supply circuit. All other configurations and circuit operations are the same, and a description thereof will be omitted.

FIG. 10 is a conceptual diagram showing the effect of the present invention with respect to a conventional switching power supply. As shown in this figure, in the conventional switching power supply device shown in FIG. 11, when the primary side power supply voltage VI is within a certain range around the controlled secondary side power supply voltage VS, FIG. As shown in (1) and (2), there is a great possibility that the first and second problems described above will occur. In the present invention, when the primary power supply voltage VI reaches the value of the controlled secondary power supply voltage VS, the switching power supply switches without any problem as shown in FIG. Therefore, in each of the above-described embodiments, the conventional two problems, that is, both the step-down switching power supply operation and the step-up switching power supply operation are stopped, so that the switching control operation to the secondary power supply is stopped, and the primary power supply is stopped. Voltage fluctuations can be transmitted directly to the secondary side power supply voltage, and step-down switching power supply operation and step-up switching power supply operation can be prevented from occurring at the same time, reducing the power conversion efficiency of the power supply. The switching power supply operation can be switched automatically and without any adjustment process.

[0078]

As described above, according to the present invention, the step-up / step-down switching circuit generates the operation mode designating signal, and the switching control logic circuit, in accordance with the operation mode designated by the operation mode designating signal, Since only one of the step-down switching circuit and the step-up switching circuit is switched, the switching control of the secondary power supply may stop when the step-down switching power supply operation and the step-up switching power supply operation are switched. ,
A switching power supply device that automatically switches between a step-down switching power supply operation and a step-up switching power supply operation stably without lowering the power conversion efficiency of the power supply can be realized. Therefore, the switching control operation to the secondary-side power supply is stopped by stopping both of the conventional two problems, that is, the step-down switching power supply operation and the step-up switching power supply operation, and the fluctuation of the primary-side power supply voltage is not changed. Side power supply voltage, and the step-down switching power supply operation and the step-up switching power supply operation can be avoided at the same time, thereby reducing the power conversion efficiency of the power supply. ,
In addition, switching can be performed without any adjustment process.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a switching power supply device according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a switching power supply device according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram showing another example of the switching power supply according to the second embodiment of the present invention.

FIG. 4 is a configuration diagram of a switching power supply device according to a third embodiment of the present invention.

FIG. 5 is a more specific configuration diagram of a switching power supply device according to a third embodiment of the present invention.

FIG. 6 is a configuration diagram showing another example of the switching power supply according to the third embodiment of the present invention.

FIG. 7 is a timing chart for explaining the operation in the first embodiment of the present invention.

FIG. 8 is a timing chart for explaining an operation according to the second embodiment of the present invention;

FIG. 9 is a timing chart for explaining an operation according to the third embodiment of the present invention.

FIG. 10 is an explanatory diagram of an effect of the present invention.

FIG. 11 is a configuration diagram of a conventional switching power supply device.

FIG. 12 is a timing chart for explaining the operation of a conventional switching power supply device.

FIG. 13 is a timing chart for explaining the operation of a conventional switching power supply device.

[Description of Signs] 1 Primary-side power supply 2 Error amplifier 3 Reference voltage source 4 Triangular wave generation circuit 5 Control signal switching circuit 6 Step-up / step-down switching circuit 7 Comparator 8 Switching control logic circuit 9 Step-down switching circuit 10 Step-up switching circuit 11 Load circuit C1 Smoothing capacitor C2 Capacitor R1, R2, R3 Resistance VR1 Variable resistor Q1 Step-down switching element Q2 Step-up switching element D1, D2 Diode L1 Coil

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hiroki Matsunaga 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd. (reference) 5H730 AA14 AA16 AS01 AS04 AS05 BB13 BB14 BB57 BB86 BB88 DD04 DD32 FD01 FG05 FG25

Claims (3)

[Claims] A step-down switching circuit for stepping down a secondary power supply voltage from a primary power supply voltage of an input voltage; and a step-up switching circuit for boosting the secondary power supply voltage from the primary power supply voltage. A switching circuit, a coil having both ends connected to each of the step-down and step-up switching circuits, and a capacitor for smoothing a switching output of each of the step-down and step-up switching circuits and generating the secondary-side power supply voltage, An error amplifier that compares the secondary power supply voltage with a reference voltage and amplifies the difference voltage; an inversion circuit that generates an inversion voltage obtained by inverting an output voltage of the error amplifier with reference to a predetermined voltage; The output voltage of the amplifier is compared with the predetermined voltage or the inverted voltage, and the comparison result is used as an operation mode between the step-down switching power supply operation and the step-up switching power supply operation. A step-up / step-down switching circuit that outputs as an operation mode designating signal for designating an operation mode, and an output voltage of the error amplifier and the inversion voltage generated by the inversion circuit, and are designated by the operation mode designating signal. A selection circuit that outputs one of the output voltage of the error amplifier and the inversion voltage in accordance with an operation mode of the error amplifier; a triangular wave generation circuit that generates a triangular wave signal; an output of the selection circuit and the triangular wave of the triangular wave generation circuit A comparator for generating an original signal for the switching operation of the step-down switching circuit and the step-up switching circuit by comparing the signal with a signal; an operation mode designation signal for the step-up / step-down switching circuit; and a switching operation generated by the comparator And the operation mode designating signal is a step-down switching power supply operation. When the operation mode is designated, the step-down switching circuit performs a switching operation according to the original signal of the switching operation and stops the switching operation of the step-up switching circuit, and the operation mode designation signal switches the step-up switching power supply operation mode. A switching control logic circuit that, when specified, causes the boosting switching circuit to perform a switching operation in accordance with an original signal of the switching operation and stops the switching operation of the step-down switching circuit. 2. A step-down switching circuit for stepping down a secondary power supply voltage from a primary power supply voltage of an input voltage, and a step-up switching circuit for boosting the secondary power supply voltage from the primary power supply voltage. A switching circuit, a coil having both ends connected to each of the step-down and step-up switching circuits, and a capacitor for smoothing a switching output of each of the step-down and step-up switching circuits and generating the secondary-side power supply voltage, An error amplifier that compares the secondary power supply voltage with a reference voltage and amplifies the difference voltage, an inversion circuit that generates an inversion voltage obtained by inverting an output voltage of the error amplifier with reference to a predetermined voltage, Comparing the secondary side power supply voltage with the secondary side power supply voltage,
When the primary-side power supply voltage is higher than the secondary-side power supply voltage, the inverted voltage generated by the inverting circuit is compared with the predetermined voltage, and the comparison result is referred to as a step-down switching power supply operation and a step-up switching power supply. Output as an operation mode designating signal for designating an operation mode with the operation, and when the primary power supply voltage is lower than the secondary power supply voltage, compare the output voltage of the error amplifier with the predetermined voltage; A step-up / step-down switching circuit that outputs a result of the comparison as an operation mode designating signal for designating an operation mode between the step-down switching power supply operation and the step-up switching power supply operation; and an output voltage of the error amplifier and the inversion circuit. And the output voltage of the error amplifier according to the operation mode designated by the operation mode designation signal. A selection circuit that outputs one of the inverted voltage and the inverted voltage; a triangular wave generation circuit that generates a triangular wave signal; and a step-down switching circuit by comparing an output of the selection circuit with the triangular wave signal of the triangular wave generation circuit. And a comparator for generating an original signal for the switching operation of the step-up switching circuit; an operation mode specifying signal for the step-up / step-down switching circuit and an original signal for the switching operation generated by the comparator; When the signal designates the step-down switching power supply operation mode, the step-down switching circuit performs a switching operation according to the original signal of the switching operation and stops the switching operation of the step-up switching circuit, and the operation mode designating signal is boosted. Type switching power supply operation mode Switching power supply and a switching control logic circuit for stopping the switching operation of the step-down switching circuit causes the switching operation in response to the step-up switching circuit to the original signal of the switching operation when the constant. 3. A step-down switching circuit for stepping down a secondary power supply voltage from a primary power supply voltage of an input voltage, and a step-up switching circuit for boosting the secondary power supply voltage from the primary power supply voltage. A switching circuit, a coil having both ends connected to each of the step-down and step-up switching circuits, and a capacitor for smoothing a switching output of each of the step-down and step-up switching circuits and generating the secondary-side power supply voltage, An error amplifier that compares the secondary power supply voltage with a reference voltage and amplifies the difference voltage; a triangular wave generating circuit that generates a first triangular wave signal; and a first triangular wave signal generated by the triangular wave generating circuit. An inverting circuit for generating a second triangular wave signal inverted with reference to a voltage, comparing the output voltage of the error amplifier with the predetermined voltage, and comparing the comparison result with a step-down switch. And a step-up / step-down switching circuit for outputting an operation mode designating signal for designating an operation mode between a switching power supply operation and a boosting switching power supply operation; a first triangular wave signal generated by the triangular wave generation circuit; A second triangular wave signal to be input, and a selection circuit that outputs one of the first triangular wave signal and the second triangular wave signal according to an operation mode designated by the operation mode designation signal; A comparator for generating an original signal for a switching operation of the step-down switching circuit and the step-up switching circuit by comparing an output voltage of the error amplifier with an output of the selection circuit; and an operation mode of the step-up / step-down switching circuit. A designation signal and an original signal of the switching operation generated by the comparator are inputted, and the operation mode is designated. When the signal designates the step-down switching power supply operation mode, the step-down switching circuit performs a switching operation according to the original signal of the switching operation and stops the switching operation of the step-up switching circuit, and the operation mode designating signal is boosted. Switching power supply device comprising: a switching control logic circuit for causing the boosting switching circuit to perform a switching operation in accordance with an original signal of the switching operation when designating a switching power supply operation mode and for stopping the switching operation of the step-down switching circuit. .