JP5252214B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply, and more particularly to a switching power supply that has a power conversion transformer and supplies power to a load circuit in a state where a primary side and a secondary side are insulated.

2. Description of the Related Art Conventionally, various insulating switching power supply devices including a flyback power supply device including a flyback transformer are known.
In these switching power supply devices, the switching duty (for example, on-duty) is controlled in order to suppress the inrush current when the switching power supply device is started up (at the start of transformation), and the output voltage value is set at a constant output voltage change rate. A soft start operation is performed in which the output voltage value is gradually increased and the soft start operation is performed so as to slowly reach the target output voltage value.
According to the switching power supply apparatus that performs these soft start operations, it is possible to reduce the inrush current at the time of starting the power supply and to suppress the overshoot of the output voltage at the time of starting.
JP 2006-50688 A

In the soft start operation in the above conventional switching power supply device, for example, the control is performed by detecting the charging voltage of the capacitor using a constant current source and limiting the upper limit value of the on-duty. Since the rate of change of duty is constant, if the input voltage (power supply voltage) is different, the start-up time will be different, and if the input voltage is high, the inrush current will be high although it is suppressed. there were.
As a result, when a circuit is connected to the switching power supply device and driven, the start timing (time until the start of operation) of the circuit is not constant. For example, a plurality of ECUs connected to different switching power supplies If the ECU startup time varies greatly even if communication between the two is performed, authentication cannot be performed correctly and communication cannot be established. There is a problem that the circuit design becomes complicated, for example, it is necessary to configure it so that it stands up.

In order to solve this, in the technique described in Patent Document 1, a time setting capacitor for setting the soft start operation time is provided, and the voltage level across the time setting capacitor is set based on the commercial AC power supply level. By changing the amount of change per unit time and changing the switching frequency of the switching element according to the voltage level at both ends of this time setting capacitor, it is controlled so as to be the soft start operating time, commercial AC power supply Regardless of the level (100 V or 200 V), the soft start operation time in the power supply circuit is made constant.
However, it has not always been possible to follow a situation in which the power supply voltage changes as needed, such as in-vehicle batteries.
Accordingly, an object of the present invention is to enable switching that can make the start-up time constant while suppressing the inrush current regardless of the power supply voltage, and can suppress fluctuations in the output voltage during the soft start operation. It is to provide a power supply device.

  In order to solve the above-described problem, a first aspect of the present invention includes a switching element, and suppresses an inrush current when an input voltage is transformed according to an on-duty of the switching element to obtain an output voltage having a predetermined target voltage value. A switching power supply device that performs a soft start operation, the capacitance for holding the on-duty upper limit value of the switching element during the soft start operation as a terminal voltage, and the input voltage value at the start of the transformation An on-duty control circuit for increasing the voltage between the terminals at a predetermined rate based on the detected input voltage value so that the time until the target voltage value is detected is constant, and the terminal of the capacitor A drive control signal corresponding to the on-duty upper limit value based on the inter-voltage is generated and output to the switching element. Characterized by comprising the etching control circuit.

According to the above configuration, the on-duty control circuit detects the input voltage value at the start of voltage transformation, and based on the detected input voltage value, the inter-terminal voltage is determined so that the time until reaching the target voltage value is constant. Is increased at a predetermined rate.
As a result, the switching control circuit generates a drive control signal corresponding to the on-duty upper limit value based on the inter-terminal voltage of the capacitor, and outputs it to the switching element.

  According to a second aspect of the present invention, in the first aspect, the on-duty control circuit calculates an on-duty of the switching element for obtaining the target voltage based on the detected input voltage value, and calculates the calculated on-duty. Is divided by the time to reach the target voltage value, which is a constant value, to calculate the amount of increase in on-duty per unit time, and the terminal voltage is calculated at a rate corresponding to the amount of increase per unit time. It is characterized by increasing.

  According to the above configuration, the on-duty control circuit calculates an increase amount of the on-duty per unit time by dividing the on-duty calculated based on the detected input voltage value by a constant time, and the unit The voltage between terminals is increased at a rate corresponding to the increase per hour.

According to a third aspect of the present invention, in the second aspect, the on-duty control circuit includes a current supply source that varies a charging current amount supplied to the capacitor, and increases the on-duty per unit time. In addition, a charging current is supplied so that the inter-terminal voltage increases.
According to the above configuration, the current supply source of the on-duty control circuit supplies the charging current so that the inter-terminal voltage increases in accordance with the increase amount of the on-duty per unit time.

According to a fourth aspect of the present invention, in the second aspect or the third aspect, the on-duty control circuit approximates a relationship between an on-duty for obtaining the target voltage value and an input voltage value by a straight line or a broken line. The on-duty of the switching element for obtaining the target voltage is calculated based on the detected input voltage value.
According to the above configuration, the on-duty control circuit determines the on-duty of the switching element for obtaining the target voltage based on the relationship between the on-duty approximated by a straight line or a broken line and the input voltage value and the detected input voltage value. calculate.

  According to the first aspect of the present invention, the on-duty control circuit detects the input voltage value at the start of transformation, and based on the detected input voltage value so that the time until reaching the target voltage value is constant. The switching control circuit generates a drive control signal corresponding to the on-duty upper limit value based on the inter-terminal voltage of the capacitor and outputs it to the switching element, so that the input voltage value is affected. In addition, while suppressing the inrush current, the time to reach the target voltage value can be made constant, and fluctuations in the output voltage during the soft start operation can be suppressed.

According to the second aspect of the present invention, in addition to the effect of the first aspect, it is possible to quickly calculate the duty for obtaining the target voltage value corresponding to the input voltage value.
According to the third aspect of the present invention, in addition to the effect of the second aspect, the current supply source supplies the charging current so that the inter-terminal voltage increases in accordance with the increase amount of the on-duty per unit time. Therefore, the upper limit value of the on-duty can be controlled with a simple configuration, and as a result, the time to reach the target voltage value can be reliably controlled.
According to the fourth aspect of the present invention, in addition to the effects of the second aspect or the third aspect, it is possible to calculate the duty for quickly obtaining the target voltage value corresponding to the input voltage value with a simple configuration.

Next, preferred embodiments of the present invention will be described with reference to the drawings.
First, prior to specific description, the principle of the present invention will be described.
FIG. 1 is an explanatory diagram of a schematic configuration of the present invention.
A power supply device 10 configured as a switching power supply device includes a power conversion transformer 11 having a switching element connected to an input side (primary side) coil, and a primary side input voltage Vin input from a power source 12. Is converted to a predetermined output voltage Vout and output to a predetermined load circuit 13 connected to the secondary side, and a duty setting for detecting the input voltage Vin and setting an on-duty at startup Based on the duty setting circuit 15 that outputs the signal Sdset and the duty setting signal Sdset, the duty of the switching element is set so that the time (start-up time) until the output voltage reaches the target voltage value is constant regardless of the power supply voltage. And a soft start setting circuit 16 for changing the rate of change.

According to the above configuration, when the power supply apparatus 10 is activated, the duty setting circuit 15 outputs the duty setting signal Sdset for detecting the input voltage Vin and setting the on-duty at the time of activation to the soft start setting circuit 16. To do.
The soft start setting circuit 16 changes the duty change rate of the switching element based on the duty setting signal Sdset so that the time (start-up time) until the output voltage reaches the target voltage value is constant.
As a result, the power conversion circuit 14 converts the primary-side input voltage Vin input from the power supply 12 into a predetermined output voltage Vout and outputs it to the predetermined load circuit 13 connected to the secondary side. The rate of change of the output voltage Vout in the conversion circuit 14 is controlled so that the startup time is constant.

  As described above, the power conversion circuit 14 can make the time until the voltage value of the output voltage Vout reaches a predetermined target voltage value, that is, the startup time, is constant when the power supply device 1 is started. Therefore, it is not necessary to perform complicated control of the circuit rise timing on the load circuit 13 side while suppressing the overshoot of the output voltage at the start-up, and the circuit configuration of the load circuit 13 can be simplified. Become. In this case, the constant start-up time means that the start-up time falls within a predetermined time range in consideration of a predetermined margin, and the predetermined margin is determined according to the system or device of the power supply destination. .

FIG. 2 is a schematic configuration diagram of a motor driving device using the power supply device of the embodiment.
The motor drive device 20 is a device that drives an electric motor in an electric vehicle or a hybrid vehicle, and includes a battery 12 that is a power source, a smoothing capacitor 22 that smoothes a DC power source supplied from the battery 12, A controller 23 that centrally controls the motor drive device 20, an inverter circuit 24 that includes a plurality of IGBTs (Insulated Gate Bipolar Transistors), an IGBT driver unit 25 that drives the IGBT that constitutes the inverter circuit 24, and an inverter circuit 24 And a current sensor 27-U, 27-V, 27-W for detecting a driving current of each phase of the three-phase AC motor 26.
In this case, if the battery 12 has a rated output of 24 V, for example, the actual output voltage range depends on the state of charge, but considering voltage drops such as when the engine is started (when the starter motor is driven), It is about 21V.

The controller 23 is configured as a microcomputer, and includes an MPU, a ROM, and a RAM (not shown). The MPU performs various processes using the RAM as a work area based on a control program stored in the ROM in advance.
The inverter circuit 24 includes IGBT series circuits 24U, 24V, 24W having two IGBTs connected in series, and the IGBT series circuits 24U, 24V, 24W are connected in parallel between the positive electrode and the negative electrode of the battery 12.

Here, since the IGBT series circuits 24U, 24V, and 24W have the same circuit configuration, the IGBT series circuit 24U will be described as an example.
The IGBT series circuit 24U includes an IGBT 31H constituting a positive arm, a diode 32H connected in parallel between the collector and emitter of the IGBT 31H, a capacitor 33H connected in parallel between the collector and emitter of the IGBT 31H, and a negative arm. , And a diode 32L connected in parallel between the collector and emitter of the IGBT 31L, and a capacitor 33L connected in parallel between the collector and emitter of the IGBT 31L.
Here, the gates of the IGBTs 31 </ b> H and 31 </ b> L are connected to the IGBT driver unit 25.

The IGBT driver unit 25 includes U-phase IGBT drive units 25UH and 25UL corresponding to the U-phase, V-phase IGBT drive units 25VH and 25VL corresponding to the V-phase, and W-phase IGBT drive units 25WH and 25WL corresponding to the W-phase. The corresponding IGBTs 31H and 31L are driven under the control of the controller 23.
The current sensors 27-U, 27-V, 27-W detect currents flowing through the corresponding phases, and output current detection signals SIU, SIV, SIW to the controller 23.
In the above configuration, the U-phase IGBT drive units 25UH and 25UL, the V-phase IGBT drive units 25VH and 25VL, the W-phase IGBT drive units 25WH and 25WL, and the corresponding IGBT correspond to the load circuit 13 for each system.

FIG. 3 is a schematic configuration block diagram of the controller.
The controller 23 compares the voltage dividing circuit 41 for detecting the input voltage Vin from the power source 12 configured as a battery with the divided voltage Vinx and a predetermined offset voltage VOFST, and controls the current control voltage with a predetermined gain. A differential amplifier 42 that outputs a signal VCT1, a constant current circuit 43 that supplies a constant current corresponding to the current control voltage signal VCT1, and a constant current supplied from the constant current circuit 43 are supplied to charge the capacitor 45. A voltage dividing circuit 44 for generating a charging voltage; and a capacitor 45 charged by the charging voltage and held at a voltage VSFT corresponding to an on-duty upper limit value for controlling a voltage change rate of the output voltage Vout. Yes.
In the above configuration, the offset voltage VOFST and the gain of the differential amplifier 42 are adjusted according to the configuration of the load circuit 13, and the current control voltage signal VCT1 output from the differential amplifier 42 is when the input voltage Vin is low. The current amount from the constant current circuit 43 is controlled to be increased. When the input voltage Vin is high, the current amount from the constant current circuit 43 is controlled to be decreased.

  Further, the controller 23 divides the voltage of the current supplied from the DC current source 46 for supplying the current for generating the on-duty limiter voltage VDMX for limiting the predetermined maximum on-duty, and the voltage of the current supplied from the DC current source. The voltage dividing circuit 47 for generating the duty limiter voltage VDMX, the feedback voltage VFB of the voltage applied to the load circuit 13 on the secondary side, and the reference voltage VREF as a reference of the output voltage are compared, and the output voltage corresponding to that time The error amplifier 48 that outputs the error signal Verr is compared with the output voltage error signal Verr and the voltage VSFT. When the voltage VSFT is less than the output voltage error signal Verr, the voltage VSFT approaches the output voltage error signal Verr. Output the duty control signal voltage Vdut and output voltage error signal V When rr exceeds the on-duty limiter voltage VDMX, a duty limiter 49 that outputs the on-duty limiter voltage VMDX as the duty control signal voltage Vdut, and an oscillator that generates a predetermined triangular wave signal for PWM control (triangular wave generation circuit) ) 50, the triangular wave signal output from the oscillator 50 and the duty control signal voltage Vdut are compared, and the PWM control signal CPWM is output to the gate of the switching transistor 52 to perform the switching operation. And.

The controller 23 further includes a power conversion circuit 14 having a power conversion transformer 11 configured as a flyback transformer. The power conversion circuit 14 is applied with an input voltage Vin on a primary coil 53 of the power conversion transformer 11. The output voltage Vout is output to the load circuit 13 through the secondary coil 54, the diode 55 that rectifies the output voltage, and the capacitor 56 for stabilizing the output voltage.
At this time, the voltage dividing circuit 57 provided in parallel with the capacitor 56 divides the output voltage Vout, generates a feedback voltage VFB, and outputs it to the error amplifier 48.

Next, the operation of the embodiment will be described.
At the time when the power supply device 10 is activated and starts to transform, the PWM control signal CPWM is not output from the comparator 51 to the switching transistor 52 and power conversion is not performed. Therefore, it flows only to the voltage dividing circuit 41 side.
As a result, the input voltage Vin from the power supply 12 is divided by the voltage dividing circuit 41, and the divided voltage Vinx is compared with the offset voltage VOFST in the differential amplifier 42, and a current control voltage corresponding to the difference voltage. The signal VCT1 is supplied to the constant current circuit 43.

Accordingly, the constant current circuit 43 supplies a constant current corresponding to the current control voltage signal VCT1, that is, a constant current corresponding to the input voltage Vin, to the voltage dividing circuit 44.
The voltage dividing circuit 44 divides the current supplied by the constant current circuit 43, and the capacitor 45 is charged with a predetermined charging voltage corresponding to the input voltage Vin.
That is, the capacitor 45 is charged with a high charge voltage when the input voltage Vin is low, and is charged with a low charge voltage when the input voltage Vin is high.
Therefore, when the input voltage Vin is low, a voltage VSFT that changes so that the duty increases quickly is input to the duty limiter 49, and when the input voltage Vin is high, the duty changes so that the duty increases slowly. The voltage VSFT is input.
At this time, since the output voltage error signal Verr input from the error amplifier 48 to the duty limiter 49 is relatively low, the duty control signal voltage Vdut corresponding to the voltage VSFT is output from the duty limiter 49.

Here, the setting of the duty for making the time (start-up time) to reach a predetermined target voltage constant even when the power supply voltage, that is, the input voltage Vin varies will be described.
The output voltage Vout on the secondary side of the power conversion transformer 11 can be expressed by the following equation, where N is the transformer winding ratio and D is the on-duty.
Vout = N × Vin × D / (1-D)
When this equation is modified, the on-duty D can be expressed as the following equation.
D = Vout / (N × Vin + Vout)
Therefore, if the duty control signal voltage Vdut is controlled so that the on-duty D that satisfies the above equation is satisfied, the startup time can be made constant.

The above equation is an ideal circuit. In the actual circuit, when considering the forward voltage Vf of the diode 55 and the collector-emitter saturation voltage Vsat of the switching transistor 52, the on-duty D is It is expressed as an expression.
D = (Vout + Vf) / {N × (Vin−Vsat) + (Vout + Vf)}
With the above configuration, the start-up time can be made constant within a wide range of input voltage Vin. However, since the circuit for performing division is complicated in configuration, it is practically simplified in configuration. Is preferred.

FIG. 4 is a diagram for explaining the relationship between the input voltage and the on-duty of the switching element.
FIG. 5 is a diagram for explaining the relationship between the input voltage and the startup time.
More specifically, as shown in FIG. 4, the relationship between the input voltage Vin and the on-duty has a downwardly convex characteristic as indicated by the symbol L0D, and the on-duty value gradually decreases. However, as indicated by reference numeral L1D, an approximate relationship is used in which the on-duty values of the input voltages at both ends are connected by a straight line within the range of the assumed input voltage Vin (in FIG. 4, 6 to 24 volts). For example, as shown in FIG. 5, with the start time at the input voltage Vin at both ends as a reference (normalized to 1), the start time is 0.7 times when the start time is the earliest (input voltage Vin = around 15 volts). When the on-duty is not controlled, the maximum startup time is 0.2 times, and the startup time ratio is 5 times. Very difference So that the resulting.
Therefore, according to the present embodiment, it is possible to greatly suppress the change in the activation time. Furthermore, when the start-up time is constant, the start-up time is adjusted to the longer side, so that the inrush current is also suppressed.

FIG. 6 is an explanatory diagram of another approximation method for approximating the on-duty with the input voltage.
In the above explanation, the on-duty is approximated by a straight line. However, when approximating by one diffraction line, as shown by a symbol L2 in FIG. The time difference can be reduced.

FIG. 7 is an explanatory diagram of another aspect of the controller.
7 differs from FIG. 3 in that a constant current corresponding to the input voltage Vin is supplied to the voltage dividing circuit 44, whereas the output voltage VCT2 of the differential amplifier 42A is directly applied to the voltage dividing circuit 44. It is a point.
According to the above configuration, the differential amplifier 42A supplies the output voltage VCT2 to the voltage dividing circuit 44.
The voltage dividing circuit 44 divides the output voltage VCT2 applied by the differential amplifier 42A, and the capacitor 45 is charged with a predetermined charging voltage corresponding to the output voltage VCT2 of the differential amplifier 42A.
That is, when the output voltage VCT2 of the differential amplifier 42A is low and the difference between the input voltage Vin and the target voltage value is small, the capacitor 45 is charged with a high charge voltage, and the difference between the input voltage Vin and the target voltage value. When is large, the battery is charged with a low charging voltage.
Therefore, when the difference between the input voltage Vin and the target voltage value is small, a voltage VSFT that increases the duty quickly is input to the duty limiter 49, and when the difference between the input voltage Vin and the target voltage value is large. The voltage VSFT that increases the duty slowly is input.

At this time, since the output voltage error signal Verr input from the error amplifier 48 to the duty limiter 49 is relatively low, the duty control signal voltage Vdut corresponding to the voltage VSFT is output from the duty limiter 49.
As described above, also in this configuration, the start-up time can be made constant in a wide input voltage Vin range.
As described above, according to each of the above embodiments, it is possible to make the time (start-up time) until the output voltage reaches the target voltage value constant regardless of the power supply voltage. In particular, the rectifier diode is provided on the secondary side because the time (start-up time) until the target voltage value is reached by increasing the on-duty upper limit value without increasing the switching frequency is constant. However, a sufficient coupling time can be secured, and fluctuations in the output voltage can be suppressed.
In the above description, the case of a switching power supply device using a flyback transformer as the power conversion transformer has been described. However, the present invention is not limited thereto, and any switching power supply device having a power conversion switching element may be used. The same applies.

It is outline | summary structure explanatory drawing of this invention. It is a schematic block diagram of the motor drive device using the power supply device of embodiment. It is a general | schematic block diagram of a controller. It is a figure explaining the relationship between an input voltage and the on-duty of a switching element. It is a figure explaining the relationship between an input voltage and starting time. It is explanatory drawing of the other approximation method for approximating on-duty with an input voltage. It is explanatory drawing of the other aspect of a controller.

DESCRIPTION OF SYMBOLS 10 Power supply device 11 Power conversion transformer 12 Power supply 13 Load circuit 14 Power conversion circuit 15 Duty setting circuit (on-duty control circuit)
16 Soft start setting circuit (on-duty control circuit)
41 Voltage Divider 42, 42A Differential Amplifier 43 Constant Current Circuit (On Duty Control Circuit)
44 Voltage divider circuit 45 Condenser (capacity)
46 DC current source 47 Voltage divider circuit 48 Error amplifier 49 Duty limiter (on-duty control circuit)
50 Oscillator (switching control circuit)
51 Comparator (Switching control circuit)
52 Switching transistor (switching element)
53 Primary coil 54 Secondary coil 55 Diode 56 Capacitor 57 Voltage divider circuit CPWM PWM control signal (drive control signal)
Vin input voltage Vout output voltage

Claims (4)

A switching power supply device having a switching element and performing a soft start operation to suppress an inrush current when transforming an input voltage according to an on-duty of the switching element to obtain an output voltage of a predetermined target voltage value,
Capacitance for holding the on-duty upper limit value of the switching element during the soft start operation as a voltage between terminals,
An on-voltage that increases the inter-terminal voltage at a predetermined rate based on the detected input voltage value so that the input voltage value at the start of the transformation is detected and the time to reach the target voltage value is constant. A duty control circuit;
A switching control circuit that generates a drive control signal corresponding to an on-duty upper limit value based on a voltage between terminals of the capacitor, and outputs the drive control signal to the switching element;
A switching power supply device comprising: The switching power supply device according to claim 1,
The on-duty control circuit calculates an on-duty of the switching element for obtaining the target voltage based on the detected input voltage value, and reaches the target voltage value where the calculated on-duty is a constant value. The switching power supply device is characterized in that an increase amount per unit time of on-duty is calculated by dividing by a period of time, and the inter-terminal voltage is increased at a rate corresponding to the increase amount per unit time. The switching power supply device according to claim 2,
The on-duty control circuit has a current supply source that makes a charging current amount supplied to the capacitor variable,
A switching power supply device characterized in that a charging current is supplied so that the inter-terminal voltage increases in accordance with an increase amount of the on-duty per unit time. In the switching power supply device according to claim 2 or 3,
The on-duty control circuit approximates a relationship between an on-duty for obtaining the target voltage value and an input voltage value by a straight line or a broken line, and obtains the target voltage based on the detected input voltage value. Calculating an on-duty of the switching element;
The switching power supply device characterized by the above-mentioned.

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