JP3434788B2 - Semiconductor device for switching power supply - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device for controlling a switching power supply, and more particularly to a semiconductor device for a switching power supply which can reduce power consumption under a light load.

[0002]

2. Description of the Related Art A conventional semiconductor device for a switching power supply will be described with reference to the drawings.

FIG. 7 shows a circuit configuration of a switching power supply device using a conventional semiconductor device for a switching power supply in which an input side and an output side are electrically insulated.

A semiconductor device for a switching power supply has a switching element 1 composed of, for example, a power MOSFET.
04 and a control circuit 130 for controlling the switching element 104.

In the switching power supply device shown in FIG. 7, for example, the alternating current from the commercial power supply input to the main input terminal is a rectifier 101 composed of a diode bridge or the like.
Is rectified by. Then, it is smoothed by the input capacitor 102 and becomes a DC voltage Vin, which is input to the transformer 103 for power conversion. The transformer 103 has a primary winding 103a, an auxiliary winding 103b, and a secondary winding 103c, and the generated DC voltage Vin is the primary winding 103a.
Entered in.

[0006] DC voltage Vin input to the primary winding 103a of the transformer 103 is controlled by the switching element 104. At this time, the secondary winding 10 of the transformer 103 is switched by the switching operation of the switching element 104.
Electromotive force due to electromagnetic induction is generated in 3c.

The current due to the electromotive force generated in the secondary winding 103c is applied to the diode 11 connected to the secondary winding 103c.
The output voltage Vo is rectified and smoothed by 0 and the output capacitor 111, and is supplied to the load 112 as DC power of the output voltage Vo.

[0008] Also electromotive <br/> force is generated in the auxiliary winding 103b of the transformer 103, the AC electric <br/> stream that is output from the auxiliary winding 103b is composed of a diode 121 and a capacitor 122 auxiliary power supply unit 120 Is rectified and smoothed to generate the auxiliary power supply voltage Vcc.

The control circuit 130 driven by the auxiliary power supply voltage Vcc outputs a control signal to the gate of the switching element 104. Here, the auxiliary power supply voltage Vcc is proportional to the output voltage Vo supplied from the secondary winding 103c of the transformer 103 to the load 112, and is also used as a feedback signal for stabilizing the output voltage Vo.

The control circuit 130 includes a switching element 10
Oscillator 131 which outputs the switching signal applied to
And an error amplifier 132 that outputs an error voltage signal VEAO composed of the difference between the auxiliary power supply voltage Vcc and the reference voltage, and an element current detection circuit that detects a drain current ID flowing through the switching element 104 and outputs an element current detection signal VCL. 1
33, error voltage signal VEAO and element current detection signal VC
It has a comparator 134 that compares L with each other and outputs a comparison result, and a switching signal control circuit 135 that controls the output of the switching signal based on the comparison signal.

The switching signal control circuit 135 receives the clock signal CLK from the oscillator 131 at its set terminal and receives the output signal of the comparator 134 at its reset terminal.
The S flip-flop circuit 136 and the oscillator 1 at the input terminal
31 receives the maximum duty cycle signal MDC from
A NAND circuit 137 that receives the output signal from the RS flip-flop circuit 136 at the other input terminal and a gate driver 138 that receives the output signal of the NAND circuit 137, inverts and amplifies the output signal, and outputs a control signal. .

The operation of the switching power supply device configured as described above will be described below.

In FIG. 7, first, immediately after the apparatus is started, when an AC current from a commercial power source is input to the rectifier 101, the input AC current is rectified by the rectifier 101 and the input capacitor 102. It is smoothed and converted into a DC voltage Vin, and the converted DC voltage Vin is applied to the primary winding 103 a of the transformer 103. At this time, the DC voltage Vin is supplied with current through the internal circuit current supply circuit 139 included in the control circuit 130, and the auxiliary power supply unit 1
Twenty capacitors 122 are charged.

After that, in the auxiliary power supply section 120, when the auxiliary power supply voltage Vcc reaches the starting voltage of the control circuit 130, the control circuit 130 starts its operation. As a result, control of the switching operation of the switching element 104 is started, and the start / stop circuit 140 stops the internal circuit current supply circuit 139.

The control circuit 130 controls the switching operation of the switching element 104 based on the auxiliary power supply voltage Vcc so that the output voltage Vo to the load 112 is stabilized at a predetermined voltage. Specifically, the output voltage Vo to the load 112 and the auxiliary power supply voltage Vcc are supplied to the transformer 10
A voltage proportional to the winding ratio of the auxiliary winding 103b and the secondary winding 103c of No. 3, and an error voltage signal VEAO from the error amplifier 132 and an element current detection from the element current detection circuit 133 to the comparator 134. The signal VCL is compared, and when both signals VEAO and VCL become equal to each other, R
A high-level output signal is output to the reset terminal of the S flip-flop circuit 136.

Next, as shown in the timing chart of FIG. 8, when the load supply current Io decreases and the load supply current Io decreases during load change, the output voltage Vo rises slightly. In response to this, the auxiliary power supply voltage Vcc of the auxiliary power supply unit 120 on the feedback side also rises, and the error amplifier 13
The error voltage signal VEAO from 2 drops.

When the error voltage signal VEAO and the device current detection signal VCL become equal to each other while the error voltage signal VEAO is lowered, such as when there is no load such as when the load is changed or in standby, and when the load is light, the comparator 134 is operated. Since a reset signal is output from the RS flip-flop circuit 136 to the reset terminal, the NAND circuit 137 outputs a signal for turning off the switching element 104 at a timing earlier than that during a steady load. As a result, the switching element 1
In No. 04, the time during which it is in the ON state during the switching operation is shortened, so the drain current ID flowing through the switching element 104 is reduced.

As described above, the control circuit 130 in the conventional semiconductor device for a switching power supply switches the switching element 1 according to the load supply current Io supplied to the load 112.
The current mode control method for controlling the magnitude of the drain current ID flowing in 04 is adopted.

[0019]

However, in the conventional semiconductor device for a switching power supply, the drain current ID flowing through the switching element 104 is reduced at the time of light load such as standby, but the circuit current of the control circuit 130 is a transformer. Since it is supplied via 103, the drain current ID cannot be completely set to 0, and the semiconductor device must be supplied with the drain current ID via the transformer 103 at all times. Therefore, even when there is no load, a certain amount of current flows, so even when there is no load, current is lost due to the switching operation of the switching element 104, and the smaller the load, the greater the proportion of current loss in the switching element 104. As a result, there is a problem in that the efficiency of the power supply is reduced and it is not possible to achieve power saving during standby of the power supply.

The present invention solves the above-mentioned conventional problems, and an object thereof is to reduce the switching loss at the time of a light load with a simple structure to reduce the power consumption and to improve the power supply efficiency in the semiconductor device for a switching power supply. Ensure that you can improve.

[0021]

Means for Solving the Problems The present invention to achieve the above object, the semiconductor device for a switching power supply, transformer
Based on the output voltage of the vessels of the auxiliary winding to generate a power supply voltage of the control circuit, based on the generated power supply voltage, and configured to stop the output of the switching signal to the switching element
In addition, a switching element and control circuit
It is formed on the conductor substrate .

Specifically, a semiconductor device for a switching power supply according to the present invention includes a transformer, and a switching element for switching and driving a primary winding of the transformer connected to a voltage source that generates a first DC voltage. , An output voltage generation circuit that is connected to the secondary winding of the transformer and that generates and outputs a second DC voltage by rectifying and smoothing the secondary output voltage of the transformer, and the operation of the switching element Connected to an auxiliary winding of a transformer that generates an output voltage proportional to the secondary output voltage, and rectifies and smoothes the output voltage to generate a power supply voltage for the control circuit. A semiconductor device for a switching power supply, which controls a switching power supply device including a power supply voltage generation circuit for controlling the switching power supply, has a first external connection terminal, a second external connection terminal, From the third external connection terminal, the switching element connected between the first external connection terminal connected to the primary winding of the transformer and the second external connection terminal, and the power supply voltage generation circuit to the third external connection terminal. external connection and terminal integrated on a single semiconductor substrate and a control circuit for a power supply voltage is supplied via a control circuit, an oscillator for generating and outputting a switching signal, the current flowing through the switching element detection And a current detection circuit that outputs as a device current detection signal,
An error amplifier that generates and outputs an error voltage signal composed of the difference between the power supply voltage and the reference voltage, and a comparator that compares the device current detection signal and the error voltage signal and outputs a compared comparison signal are input. Set state according to the switching signal
Becomes a reset state according to the input comparison signal.
Flip-flop circuit including the flip-flop circuit
For controlling the switching element according to the output signal of
A switching signal control circuit that outputs a control signal, a light load detection comparator that detects the level of an error voltage signal and switches between a lower limit voltage value and an upper limit voltage value, and outputs the light load ,
It operates according to the output signal of the detection comparator, and when the error voltage signal is smaller than the lower limit voltage value, the switching signal is
Stop being input to the flip-flop circuit, when the error voltage signal is greater than the upper limit voltage value resumes the switching signal is input to the flip-flop circuit
And it includes a light-load detection circuit and a gate means for.

According to the semiconductor device for a switching power supply of the present invention, in general, the switching power supply device is provided in the control circuit when the second DC voltage, which is the output voltage of the device, increases when the current consumed at the time of the light load decreases. The amount of current of the feedback signal to be fed back increases. As a result, the power supply voltage of the control circuit rises, so that the voltage value of the error voltage signal from the error amplifier that generates the error voltage signal composed of the difference between the power supply voltage for the control circuit and the reference voltage decreases. At this time, the light load detection circuit stops the output of the switching signal to the switching signal control circuit when the error voltage signal is smaller than the lower limit voltage value. Since the power consumption under load can be reduced, the power supply efficiency of the switching power supply device can be improved.

[0024]

[0025]

Then, with the first to third external connection terminals,
A first external connection terminal connected to the primary winding of the pressure device and a second
Switching element connected between the external connection terminal of
And from the power supply voltage generation circuit via the third external connection terminal
Control circuit to which power supply voltage is supplied on one semiconductor substrate
Integration result, the number of components of the switching power supply device overall in
And the number of external connection terminals can be reduced.

In this case, the current detection circuit is the first external
The current flowing through the switching element connected to the connection terminal is detected.
Be out is not preferred.

A semiconductor device for a switching power supply according to the present invention comprises an input terminal of a light load detection comparator and a second external connection terminal.
Is provided between the child, it is preferable that e Bei light load detection voltage adjusting means for adjusting the value of the value or the upper limit voltage of the lower limit voltage. By doing so, it is not necessary to provide the light load detection adjusting means outside the semiconductor device , and it is possible to easily absorb the variation in accuracy of other components constituting the switching power supply device.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic circuit configuration of a switching power supply device according to an embodiment of the present invention. As shown in FIG. 1, the switching power supply device according to the first embodiment uses a transformer for a first DC voltage applied to the main input terminal 10 and obtained by rectifying and smoothing an alternating current from a commercial power supply. While applying to the primary side of (transformer) 13,
The switching operation of the switching element 14 causes the output voltage generation circuit 16 provided on the secondary side of the transformer 13 to drop to the output voltage Vo, which is the second DC voltage, and output it to the main output terminal 17. It is a power supply device.

The switching power supply device according to this embodiment will be described in detail below.

The transformer 13 has a primary winding 13a, an auxiliary winding 13b and a secondary winding 13c.

A rectifier 11 including a diode bridge for rectifying an alternating current and an input capacitor 12 for smoothing the rectified signal to generate a direct voltage Vin are connected in parallel to the main input terminal 10. . The generated DC voltage Vin is input to the primary winding 13a of the transformer 13 and then to the drain terminal TD of the switching element 14 including, for example, an N-type power MOSFET. Here, the source terminal Ts of the switching element 14 is connected to the low-level side terminal of the main input terminal 10, and the control signal output from the control circuit 15 for controlling the operation of the switching element 14 is input to the gate thereof. To be done.

An output voltage generation circuit 16 is connected to the secondary winding 13c of the transformer 13. The output voltage generation circuit 16 switches the primary winding 13a to which the DC voltage Vin is applied.
First to rectify the current due to electromagnetic induction when itching
The diode 161 and the output capacitor 162 for smoothing the rectified signal.

The main output terminal 17 connected to the output voltage generation circuit 16 is connected to a load 18 between its high-level side terminal and low-level side terminal, and the load 18 supplies a load supply current Io. Flows.

A power supply circuit 19 is connected to the auxiliary winding 13b of the transformer 13 as a power supply voltage generation circuit for generating the auxiliary power supply voltage Vcc of the control circuit 15. Power supply circuit 1
9 switches the primary winding 13a to which the DC voltage Vin is applied.
It is composed of a second diode 191 for rectifying a current due to electromagnetic induction at the time of switching, and a power supply capacitor 192 for smoothing the rectified signal. In this case, the accessory
Auxiliary winding 13b includes an auxiliary power supply voltage Vcc and the output voltage Vo is provided to be proportional. Further, the auxiliary power supply voltage Vcc generated by the power supply circuit 19 is applied to the control terminal Tc of the control circuit 15.

In the present embodiment, the region surrounded by the broken line 20, that is, the switching element 14 and the control circuit 15
A region including at least three terminals of the drain terminal TD, the source terminal Ts, and the control terminal Tc that can input / output to / from the outside is referred to as a substrate formation region 20, and this substrate formation region 20 serves as one semiconductor chip. It means that it can be formed.

The on-substrate formation region 20 may be divided into a plurality of semiconductor chips instead of being formed on one semiconductor chip. However, even when the semiconductor chip is divided into a plurality of semiconductor chips, the drain terminal TD and the source terminal T
It is preferable that at least three terminals of s and the control terminal Tc are accommodated in one package capable of inputting / outputting with the outside.

The control circuit 15 receives an oscillator 21 for generating and outputting a switching signal having an oscillation frequency of about 100 kHz, which is applied to the switching element 14, and an auxiliary power supply voltage Vcc dropped through a resistor, at its antiphase terminal. , Error voltage signal VEA consisting of the difference from the reference voltage received at the positive phase terminal
An error amplifier 22 that generates and outputs O, an element current ID that flows through the switching element 14, an element current detection circuit 23 that detects the element current ID, converts the detected element current ID into a voltage, and outputs the voltage as an element current detection signal VCL, Error voltage signal VE
A device current detection comparator 24 that compares AO with the device current detection signal VCL and outputs the compared comparison signal, a switching signal control circuit 25 that controls the output of the switching signal based on the comparison signal, and an error voltage signal When VEAO is smaller than the lower limit voltage value, the switching signal control circuit 25 stops outputting the switching signal to the switching element 14, and when the error voltage signal VEAO is larger than the upper limit voltage value, the switching signal control circuit. 25
And a light load detection circuit 40 that starts outputting a switching signal. Here, the negative phase input terminal of the error amplifier 22 is the source terminal Ts of the switching element 14.
Both are connected via a resistor.

Further, the control circuit 15 has a drain terminal TD of the switching element 14 and a control terminal T of the control circuit 15.
and an internal circuit current supply circuit 29 connected to the control circuit 15 and supplying a current for starting the control circuit 15 to the control circuit 15, and connected to the output side of the internal circuit current supply circuit 29 via a switch. The control circuit 15 controls the operation of the switching signal control circuit 25 when the control circuit 15 is started or stopped.
And a stop circuit 30.

The switching signal control circuit 25 receives the output signal of the light load detection circuit 40 at the set terminal S and the output signal of the element current detection comparator 24 at the reset terminal R, and a first RS flip-flop circuit 26. The input signal of the start / stop circuit 30 receives the output signal of the start / stop circuit 30, and the second input terminal receives the maximum duty cycle signal MDC from the oscillator 21.
Receiving the RS flip-flop circuit 2 at the third input terminal.
NAND circuit 27 for receiving the output signal from 6 and NAN
The gate driver 28 includes an inverter that receives the output signal of the D circuit 27 and outputs a control signal obtained by inverting and amplifying the received output signal to the gate of the switching element 14.

The light load detection circuit 40 includes a reference voltage source 41.
And a light load detection comparator 42 that receives the error voltage signal VEAO from the error amplifier 22 at its positive phase input terminal and a reference voltage VR from the reference voltage source 41 at its negative phase input terminal, and a light load detection comparator 42 at one input terminal. The output signal VO1 of the load detection comparator 42 is received, and the clock signal C from the oscillator 21 is applied to the other input terminal.
The AND circuit 43 receives LK. The reference voltage source 41 is an output signal V of the light load detection comparator 42.
Upon receiving O1, the value of the reference voltage VR can be changed.

The light load detecting comparator 42 compares the input error voltage signal VEAO with the reference voltage VR, and when the error voltage signal VEAO is larger than the reference voltage VR,
It outputs a high level signal to the AND circuit 43.
On the other hand, when the error voltage signal VEAO is smaller than the reference voltage VR, a low level signal is output to the AND circuit 43, so that the output signal of the RS flip-flop circuit 26 becomes low level. The output of the control signal from 28 can be stopped.

On the output side of the error amplifier 22, an overcurrent protection circuit 31 composed of a PNP bipolar transistor for clamping the maximum voltage value of the error voltage signal VEAO is provided, and the error voltage signal VEAO is overcurrent protected. By causing the circuit 31 to clamp, the maximum value of the device current ID flowing in the switching device 14 is clamped.

In the switching power supply device according to this embodiment, the voltage values of the DC voltage Vin and the output voltage Vo are not limited. As an example, the value of the DC voltage Vin is 100V to 2
If the output voltage Vo is set to 00V and the value of the output voltage Vo is set to 25V, the number of parts of the switching power supply device as a whole can be significantly reduced by making the semiconductor device for switching power supply into one chip or one package, and thus the size of the power supply device can be reduced. It is possible to realize further downsizing and cost reduction.

Further, the switching element 14 has an N-type MOS.
Although the FET is used, an NPN type bipolar transistor may be used instead.

Here, an example of a concrete circuit configuration of the reference voltage source 41 is shown in FIG. As shown in FIG. 2, the reference voltage source 41 includes a first constant current source 411 having an output terminal Y connected to the negative phase terminal of the light load detection comparator 42 and a light load detection comparison on the downstream side. And a second constant current source 412 provided with a switch transistor 413 composed of a P-type MOSFET that receives the output signal VO1 from the device 42 at its input terminal X, that is, its gate. Further, the first constant current source 4
11 for outputting at least the first output current I1 of the first output current I1 and the second output current I2 of the second constant current source 412, and for generating the lower limit voltage VR1 or the upper limit voltage VR2. Resistor 414.

The operation of the reference voltage source 41 configured as above will be described.

At a steady load, the output signal VO1 of the light load detection comparator 42 is at a high level, so that the switch transistor 413 is in an off state. Therefore, the output signal V of the reference voltage source 41 at this time
R, that is, the lower limit voltage VR1 is expressed by the following equation (1), where R1 is the resistance value of the resistor 414.

VR1 = R1 × I1 (1) On the other hand, when the light load state of the device is detected, the output signal VO1 of the light load detection comparator 42 becomes a low level.
The switching transistor 413 is turned on, and the second output current I2 from the second constant current source 412 also flows into the resistor 414 at the same time. Therefore, the output signal VR of the reference voltage source 41 at this time, that is, the upper limit voltage VR2 is expressed by the following equation (2).

VR2 = R1 × (I1 + I2) (2) Thus, the output signal VO1 of the light load detection comparator 42
According to the output voltage VR of the reference voltage source 41
By outputting R1 or the upper limit voltage VR2, it is possible to cause the switching signal control circuit 25 to perform an intermittent oscillation operation as described later when the load is light.

In this embodiment, the constant current value for setting the output voltage of the reference voltage source 40 is changed based on the output signal VO1 of the light load detecting comparator 42.
Instead, based on the output signal VO1 of the light load detection comparator 42, the resistor 4 for setting the output voltage of the reference voltage source 42 is used.
The resistance value of 14 may be changed.

The details of the operation of the switching power supply device including the semiconductor device for switching power supply configured as described above will be described below with reference to the timing chart shown in FIG.

First, in the circuit diagram shown in FIG. 1, the start / stop circuit 30 connects the internal circuit current supply circuit 29 and the anode of the power supply capacitor 192 in the power supply circuit 19 until the control circuit 15 is started up. Closed to do.

Next, when the apparatus is started and an alternating current is started to be input to the main input terminal 10, the internal circuit current supply circuit 2
A current flows from 9 to the anode of the power supply capacitor 192, and the value of the auxiliary power supply voltage Vcc of the control circuit 15 rises. When the value of the auxiliary power supply voltage Vcc reaches the start-up voltage of the control circuit 15, the control circuit 15 can operate. Therefore, the start-up / stop circuit 30 includes the internal circuit current supply circuit 29 and the power supply capacitor 192 . Terminate the connection. As a result, the internal circuit current supply circuit 29 operates only at the time of startup, so that the power consumption of the control circuit 15 during normal operation can be suppressed.

Next, as shown in FIG. 3, during a steady load, the value of the reference voltage VR of the reference voltage source 41 is set to the lower limit voltage value VR1.

After that, for example, when a load change occurs such that the load supply current Io decreases, that is, the load 18 decreases.
Is excessively supplied, and the voltage value of the output voltage Vo is slightly increased. As the value of the output voltage Vo rises, the auxiliary power supply voltage Vcc of the power supply circuit 19 on the feedback side also rises.

When the auxiliary power supply voltage Vcc rises, the voltage applied to the negative phase terminal of the error amplifier 22 in the control circuit 15 rises, so that the voltage value of the error voltage signal VEAO output from the error amplifier 22 falls. . At this time, the element current detection signal V output from the element current detection circuit 23
The voltage value of CL also decreases.

As described above, the switching power supply device according to this embodiment is a so-called current mode PW in which the pulse width of the switching signal is changed by the load supply current Io.
Adopt M control method.

The light load detection comparator 42 that receives the error voltage signal VEAO at its positive phase terminal receives the error voltage signal VEA.
When the value of O becomes smaller than the lower limit voltage value VR1, AND
Since the low level signal is output to the circuit 43, the gate driver 28 of the switching signal control circuit 25 outputs only the low level control signal, and the switching operation of the switching element 14 is stopped. Almost at the same time, the output voltage VR of the reference voltage source 41 receives the low level output signal of the light load detection comparator 42 and receives the lower limit voltage value V.
The upper limit voltage value VR2 is changed from R1.

In a light load or no load state such as during standby, power is not supplied to the output voltage generation circuit 16, so that power is supplied to the load 18 only from the output capacitor 162. Therefore, the output voltage Vo gradually decreases. As a result, the error amplifier 22
Error voltage signal VEAO gradually increases, but the output voltage VR of the reference voltage source 41 is set to the upper limit voltage VR2 higher than the lower limit voltage VR1. Therefore, as shown in FIG. The switching operation is not immediately restarted.

Further, when the output voltage Vo decreases and the error voltage signal VEAO exceeds the upper limit voltage value VR2, the output signal from the light load detection comparator 42 becomes high level again, and this is received. Since the AND circuit 43 can output the high level output signal, the switching operation of the switching element 14 is restarted. Almost at the same time, the output voltage VR of the reference voltage source 41 is reset from the upper limit voltage value VR2 to the lower limit voltage value VR1 in response to the high level output signal of the light load detection comparator 42.

Next, when the switching operation by the switching element 14 is restarted in the standby state, the element current ID flowing through the switching element 14 becomes larger than the current value at the time of detecting the light load. Power supply becomes excessive, the output voltage Vo rises again, and the error voltage signal VEAO from the error amplifier 22 falls. Therefore, as described above, when the error voltage signal VEAO becomes smaller than the lower limit voltage value VR1, the switching element 14
The output of the switching signal to is stopped again.

In the present embodiment, the reference voltage VR output from the reference voltage source 41 detects the light load state to stop the switching operation, and further the reference voltage V
By changing R from the lower limit voltage value VR1 to the upper limit voltage value VR2, a hysteresis characteristic is given to the reference voltage VR so that the switching operation does not immediately start even if the error voltage signal VEAO rises. . Accordingly, while the light load or the no load is detected, the switching control of the switching element 14 is in the intermittent oscillation state in which the stop and the restart of the switching operation are repeated.

The output voltage Vo drops during the switching stop period in the intermittent oscillation state, and the degree of this drop depends on the load supply current Io. That is, as the load supply current Io decreases, the output voltage Vo decreases more slowly.

Further, the switching stop period in the intermittent oscillation state becomes longer as the load supply current Io becomes smaller. That is, the lighter the load, the less the switching operation of the switching element 14.

In the present embodiment, for example, in the case of a switching power supply having an output of 0.3 W, the conventional power supply has a power consumption of 1 W and a power supply efficiency of about 30%. Power supply consumes 0.4
It has been confirmed that the power efficiency becomes 67% at 5 W, and that low power consumption and high efficiency are achieved.

Moreover, in the semiconductor device for a switching power supply according to this embodiment, the control circuit 15 and the switching element 14 on the primary side, that is, the input side, are formed in the formation region 20 on the substrate.
Since only the semiconductor integrated circuit is included, it can be easily integrated into one package or one chip as a semiconductor integrated circuit, and the number of parts can be reduced, so that the cost can be reduced easily.

(First Modification of One Embodiment) A first modification of one embodiment of the present invention will be described below with reference to the drawings.

FIG. 5 shows a schematic circuit configuration of a semiconductor device for a switching power supply according to a first modification of the embodiment of the present invention. In FIG. 5, the same components as those shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 5, the semiconductor device for a switching power supply according to the first modification is electrically connected to the negative phase input terminal of the light load detection comparator 42 at the end of the substrate formation region 20. The light load detection voltage adjusting terminal TR is provided.

Thus, by providing the light load detection voltage adjustment resistor 51 as the detection voltage varying means, one end of which is connected to the light load detection voltage adjustment terminal TR and the other end of which is connected to the source terminal Ts, It becomes possible to appropriately adjust the lower limit voltage value VR1 and the upper limit voltage value VR2 which are the light load detection voltages. Therefore, it is possible to optimize the load supply current Io when the switching operation of the switching element 14 is stopped or restarted together with the required load during standby. As a result, the switching element 14
Also, even when the control circuit 15 is packaged or integrated into one chip, the lower limit voltage value VR1 or the upper limit voltage value VR2 of the light load detection circuit 40 can be changed according to the application of the power supply device.

(Second Modification of One Embodiment) A second modification of one embodiment of the present invention will be described below with reference to the drawings.

FIG. 6 shows a schematic circuit configuration of a semiconductor device for a switching power supply according to a second modification of the embodiment of the present invention. 6, the same components as those shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 6, the semiconductor device for a switching power supply according to the second modification has one end connected to the negative phase input terminal of the light load detection comparator 42 and the other end connected to the source terminal T.
A light load detection voltage adjusting resistor 51A as a light load detection voltage adjusting means connected to s is provided.

As a result, the resistance value of the light load detection voltage adjusting resistor 51A can be finely adjusted by a trimming technique such as a laser trimming method. As a result, the number of parts provided outside the semiconductor device for a switching power supply can be reduced.

In addition, since the light load detection voltage adjusting resistor 51A is provided in the substrate forming region 20, that is, in the semiconductor device, it is possible to absorb the variation in accuracy of other components constituting the switching power supply device. You can

The light load detection voltage adjusting resistor 51A
Alternatively, a Zener zap circuit may be used in which a plurality of Zener diodes and resistors connected in series are connected in parallel. The trimming method in this case can be performed by causing a current to flow through a Zener diode connected to a required resistor so as to obtain a desired resistance value, and shorting the Zener diode to destroy (Zap) it.

[0079]

According to the semiconductor device for a switching power supply of the present invention, an error amplifier for outputting an error voltage signal consisting of a difference between a power supply voltage for a control circuit generated by being fed back from an output voltage and a reference voltage, It has a light load detection circuit that stops the output of the switching signal to the switching element to the switching signal control circuit when the error voltage signal is smaller than the lower limit voltage value. Since the power consumption under load can be reduced, the power efficiency of the switching power semiconductor device can be improved.

[Brief description of drawings]

FIG. 1 is a schematic circuit diagram showing a switching power supply device including a semiconductor device for a switching power supply according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a reference voltage source whose output value is variable in a semiconductor device for a switching power supply according to an embodiment of the present invention.

FIG. 3 is a timing chart showing an operation of the switching power supply device including the semiconductor device for a switching power supply according to the embodiment of the present invention.

FIG. 4 is a timing chart showing reference voltages used in the light load detection comparator in the semiconductor device for a switching power supply according to the embodiment of the present invention.

FIG. 5 is a schematic circuit diagram showing a semiconductor device for a switching power supply according to a first modification of one embodiment of the present invention.

FIG. 6 is a schematic circuit diagram showing a semiconductor device for a switching power supply according to a second modification of the embodiment of the present invention.

FIG. 7 is a schematic circuit diagram showing a switching power supply device including a conventional semiconductor device for a switching power supply.

FIG. 8 is a timing chart showing the operation of the conventional switching power supply device.

[Explanation of symbols]

10 main input terminal 11 rectifier 12 input capacitor 13 transformer (transformer) 13a 1 winding 13b auxiliary winding 13c 2 winding 14 switching elements 15 control circuit 16 outputs a voltage generating circuit 161 first diode 162 output capacitor 17 main Output terminal 18 Load 19 Power supply circuit (power supply voltage generation circuit) 191 Second diode 192 Power supply capacitor 20 Substrate formation area 21 Oscillator 22 Error amplifier 23 Current detection circuit 24 Element current detection comparator 25 Switching signal control circuit 26 RS flip-flop Circuit 27 NAND circuit 28 gate driver 29 internal circuit current supply circuit 30 start / stop circuit 31 overcurrent detection circuit 40 light load detection circuit 41 reference voltage source 411 first constant current source 412 second constant current source 413 switch transistor (Switch) 41 Resistor (output voltage setting resistor) 42 Light load detection comparator 43 AND circuit 51 Light load detection voltage adjusting resistor (detection voltage varying means) 51A Light load detection voltage adjusting resistor (light load detection voltage adjusting means) ) Ts source terminal TD drain terminal Tc control terminal TR light load detection voltage adjustment terminal

─────────────────────────────────────────────────── (72) Inventor Yuji Yamanishi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Tomoko Kinoshita 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (56) References JP-A-10-304658 (JP, A) JP-A-2-186713 (JP, A) JP-A-2001-224166 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ , DB name) H02M 3/28

Claims (3)

(57) [Claims] 1. A transformer, a switching element for switching and driving a primary winding of the transformer connected to a voltage source for generating a first DC voltage, and a secondary winding of the transformer. An output voltage generation circuit that generates and outputs a second DC voltage by rectifying and smoothing the secondary output voltage of the transformer; a control circuit that controls the operation of the switching element; A power supply voltage generation circuit that is connected to the auxiliary winding of the transformer that generates an output voltage proportional to the secondary output voltage, and that rectifies and smoothes the output voltage to generate a power supply voltage of the control circuit; A semiconductor device for a switching power supply for controlling a switching power supply device, comprising: a first external connection terminal, a second external connection terminal, a third external connection terminal, Connected the switching element between the serial transformer primary winding connected to said line and the first external connection terminal and the second external connection terminal, and the power supply voltage and the third from the generator
External connection are terminals integrated on a single semiconductor substrate and said control circuit power supply voltage is supplied via the control circuit includes an oscillator for generating and outputting a switching signal, the switching element A current detection circuit that detects a flowing current and outputs it as an element current detection signal, an error amplifier that generates and outputs an error voltage signal consisting of a difference between the power supply voltage and a reference voltage, the element current detection signal and the error Compare with the voltage signal,
A comparator that outputs a compared comparison signal, and a set state according to the input switching signal
The reset state according to the input comparison signal.
And a flip-flop circuit including
A switching signal control circuit that outputs a control signal for controlling the switching element according to an output signal of the circuit, and a light signal that detects the level of the error voltage signal and switches between a lower limit voltage value and an upper limit voltage value for output. A load detection comparator ,
It operates according to the output signal of the light load detection comparator, and when the error voltage signal is smaller than the lower limit voltage value, the switching signal is input to the flip-flop circuit.
The switching signal is stopped when the error voltage signal is larger than the upper limit voltage value.
Gate that resumes being input to the lip-flop circuit
The semiconductor device for a switching power supply, characterized in that it comprises a light-load detection circuit and means. 2. The semiconductor device for a switching power supply according to claim 1, wherein the current detection circuit is connected to the first external connection terminal and detects a current flowing through the switching element. 3. A light load detection voltage adjusting means provided between the input terminal of the light load detection comparator and the second external connection terminal for adjusting the value of the lower limit voltage or the value of the upper limit voltage. The semiconductor device for a switching power supply according to claim 1 or 2, further comprising: