JP2003289665A - Switching power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a peak current. <P>SOLUTION: A PWM signal P3 is generated by an adding circuit 2 as a signal to turn on a switching element Q3 through a PWM signal P1 and a PWM signal P2, when either switching element Q1 or a switching element Q2 is ON. When an input voltage Vin increases and pulse widths of the PWM signals P1 and P2 become narrower by a PWM control 1, a pulse width of the PWM signal P3 also reduces, and a voltage Vc supplied to a center tap of a transformer T1 also decreases. By this reason, the pulse widths of the PWM signals P1 and P2 at which an output voltage Vout reaches a target voltage are kept to be wider as compared to the case when the input voltage Vin is directly supplied to the center tap of the transformer T1. As a result, a peak value of a current flowing through the switching elements Q1 and Q2 and an inrush current value of a capacitor C2 for leveling an output are suppressed to be smaller as compared to the case when the input voltage Vin is directly supplied to the center tap of the transformer T1. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a PWM (Pulse W
The present invention relates to a technique for suppressing a peak current in a switching power supply device that controls an output voltage by controlling idth modulation.

[0002]

2. Description of the Related Art As a switching power supply device which controls an output voltage by PWM control, for example, a push-pull type switching power supply device shown in FIG. 3 is known. As shown in the figure, this switching power supply device includes an electrolytic capacitor C1 for suppressing ripple of an input voltage Vin,
A non-insulated transformer T1 having a center tap, switching elements Q1 and Q2 that are two FETs, two output rectifying diodes D1 and D2, an output smoothing electrolytic capacitor C2, and a PWM control unit (PWM CNT) 1 are provided. is doing. Here, for convenience, the reactances on both sides of the center tap of the transformer T1 will be described as L1 and L2, respectively.

The PWM control unit 1 has PWM signals P1 and P2 which have pulses of a constant cycle and whose phases are shifted from each other by a half cycle.
Are applied to the switching elements Q1 and Q2, respectively. PWM
The control unit 1 sets the pulse widths of the PWM signals P1 and P2 so that the output voltage Vout becomes the target voltage.
When the output voltage Vout is larger than the target voltage, the pulse width is expanded, and when the output voltage Vout is larger than the target voltage, the pulse width is decreased. However, the PWM signal P
The maximum duty ratio of 1 and P2 is limited to a range of 50% or less.

The PWM signals P1 and P2 alternately turn on and off the switching elements Q1 and Q2, and the voltage Vc supplied to the center tap of the transformer T1.
The current due to is passed through the reactances L1 and L2 to accumulate energy. Then, during the off period of the switching elements Q1 and Q2, a current due to the energy accumulated in the reactances L1 and L2 is output to the output side, and is rectified and smoothed by the output rectifying diodes D1 and D2 and the output smoothing electrolytic capacitor C2. As a result, an output having the output voltage Vout is obtained.

[0005]

In such a switching power supply device, when the input voltage Vin fluctuates and increases,
In order to maintain the output voltage Vout at the target voltage, PWM
By the control of the control unit 1, the pulse widths of the PWM signals P1 and P2 are controlled to be small. Then, if the load connected to the output of the switching power supply is constant, as the pulse widths of the PWM signals P1 and P2 become smaller, the peak of the current flowing through the switching elements Q1 and Q2 becomes constant in order to make the energy transferred to the output constant. The value and the inrush current value of the output smoothing capacitor C2 increase.

Then, the switching elements Q1 and Q2
The increase in the peak value of the current flowing through the switching element Q
1 and Q2 increase in the amount of heat generated, and an increase in the inrush current value of the output smoothing capacitor C2 causes an increase in the amount of heat generated in the capacitor C2. Therefore, it is necessary to suppress these peak currents below the allowable level. is there.

As shown in FIG. 4, if an insulating type transformer T2 is used instead of the non-insulating type transformer T1 of the switching power supply device shown in FIG. It can be suppressed to some extent that the pulse widths of the PWM signals P1 and P2 become smaller as the pulse width increases beyond. However, for this purpose, it is necessary to increase the number of windings of the transformer T2, which inevitably results in an increase in cost and a loss due to the transformer T2. Further, depending on the conditions, there is a possibility that the pulse width of P2 becomes small as the PWM signal P1 and the peak current increase beyond the allowable level.

Therefore, an object of the present invention is to suppress the peak current in the switching power supply device which controls the output voltage by PWM control.

[0009]

In order to achieve the above object, the present invention provides a PWM (Pulse Width Modulation) for an input voltage.
) A switching power supply device for converting into an output voltage using control, a transformer, a transformer for transforming the input voltage and supplying it as a supply voltage to the transformer, and turning on / off a current flowing through the transformer by the supply voltage. A first switching element that is turned off, a rectifying and smoothing circuit that rectifies and smoothes an output current of the transformer to obtain an output voltage, and a first switching element of the first switching element that eliminates a difference between the output voltage and a predetermined target voltage. An output voltage control unit for performing PWM control of ON / OFF, and a supply voltage control circuit, wherein the transformer means includes a second switching element provided between the input voltage application point and the transformer, and the input. A smoothing circuit that smoothes a voltage supplied from a voltage power source through the second switch and supplies the smoothed voltage to the transformer as the supply voltage, Serial supply voltage control circuit, the second
PW for turning on / off the switching element is smaller as the output voltage is higher than the target voltage.
Provided is a switching power supply device which is PWM-controlled by an M signal.

According to such a switching power supply device, the supply voltage supplied to the transformer is controlled by the PWM signal in which the duty ratio becomes smaller as the output voltage becomes larger than the target voltage. Therefore, when the output voltage is higher than the target voltage, the value of the supply voltage supplied to the transformer becomes small, so that the PWM for switching the current flowing through the transformer by the supply voltage is used.
It becomes unnecessary to reduce the pulse width (duty ratio) in the control as compared with the case where the input voltage is directly supplied to the transformer. Therefore, it is possible to suppress the peak current value flowing in the switching element that switches the current flowing through the transformer according to the supply voltage and the rectifying / smoothing circuit that rectifies and smoothes the output of the transformer, and suppress the heat generation of each unit.

More specifically, the present invention is, for example, a switching power supply device for converting an input voltage into an output voltage by using PWM (Pulse Width Modulation) control, which includes a transformer having an intermediate tap and the input voltage. Between the first end of the transformer and the ground potential, and a second switching element arranged between the second end of the transformer and the ground potential. The second switching element arranged, a rectifying / smoothing circuit for rectifying and smoothing the output current of the transformer to obtain the output voltage, and the first switching circuit so that there is no difference between the output voltage and a predetermined target voltage. PWM for performing PWM control of ON / OFF of the switching element and ON / OFF of the second switching element with phases shifted from each other by a half cycle
A transformer and a supply voltage control circuit, wherein the transformer comprises a third switching element provided between an input point of the input voltage and an intermediate tap of the transformer, and a power source for the input voltage. A smoothing circuit for smoothing a voltage supplied via the third switch and supplying the smoothed voltage to the intermediate tap of the transformer as the supply voltage, wherein the supply voltage control circuit turns on / off the third switching element. PW is turned off by the PWM signal for input voltage transformation in which the duty ratio becomes smaller as the output voltage becomes larger than the target voltage.
Provided is a switching power supply device characterized by M control.

Further, according to the present invention, for example, the input voltage is set to P
A switching power supply device for converting into an output voltage by using WM (Pulse Width Modulation) control, wherein a non-insulating transformer having an intermediate tap and an intermediate tap of the non-insulating transformer for transforming the input voltage are supplied. A transformer for supplying power, a first switching element arranged between the first end of the non-insulated transformer and the ground potential,
A second switching element arranged between the second end of the non-insulating transformer and a ground potential, and a second switching element connected between both ends of the non-insulating transformer to rectify and smooth a current input from the non-insulating transformer. And a first rectifying / smoothing circuit for converting the output voltage to a predetermined target voltage so that there is no difference between the output voltage and the predetermined target voltage. And a supply voltage control circuit for PWM-controlling the on / off of the second switching element and the on / off of the second switching element in a phase shifted from each other by a half cycle, and the transformation means has the input voltage. Of the input voltage and the intermediate tap of the non-insulated transformer, and smoothing the voltage supplied from the power supply of the input voltage via the third switch, A smoothing circuit that supplies the voltage to the intermediate tap of the non-insulating transformer, the supply voltage control circuit turns on / off the third switching element, and outputs the duty as the output voltage is larger than the target voltage. P is set by the PWM signal for input voltage transformation with a small ratio
Provided is a switching power supply device characterized by WM control.

Here, in these switching power supply devices, the PWM control section includes a first output voltage control PWM signal for controlling the ON period of the first switching element, and the second switching element. A second output voltage control PWM signal for controlling the ON period of the output voltage control circuit, and the supply voltage control circuit outputs the first output voltage control PWM signal and the second output voltage control PWM signal, The ON period of the first switching element and the second period
The input voltage transformation PWM signal for turning on the third switching element may be generated during the on period of the switching element.

By doing so, it is possible to realize the control of the supply voltage with a small circuit scale without providing a dedicated PWM control function unit for generating the PWM signal for input voltage transformation.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 shows the configuration of the switching power supply device according to this embodiment. As shown in the figure, the present switching power supply device includes an electrolytic capacitor C1, a non-insulating transformer T1 having a center tap, two N-type FET switching elements Q1 and Q2, and two output rectifying diodes D.
1, D2, an electrolytic capacitor C2 for smoothing the output, a PWM control unit (PWM CNT) 1, a switching element Q3 which is a P-type FET, resistors R1 and R2 for generating a gate voltage of the switching element Q3, a reactance L3, an adding circuit ( N
OR) 2 and a reactance L4 for smoothing the output. Here, for convenience, the reactances on both sides of the center tap of the transformer T1 will be described as L1 and L2, respectively.

The PWM control unit 1 applies PWM signals P1 and P2 having pulses of a constant cycle, which are out of phase with each other by a half cycle, to the switching elements Q1 and Q2, respectively. The PWM control unit 1 widens the pulse width of the PWM signals P1 and P2 so that the output voltage Vout becomes the target voltage so that the output voltage Vout is smaller than the target voltage, and the output voltage Vout is larger than the target voltage. In this case, control is performed by reducing the pulse width. However, the PWM signal P1,
The maximum duty ratio of P2 is limited to 50% or less.

The PWM signals P1 and P2 alternately turn on and off the switching elements Q1 and Q2, and the voltage Vc supplied to the center tap of the transformer T1.
The current due to is passed through the reactances L1 and L2 to accumulate energy. Then, during the off period of the switching elements Q1 and Q2, the current due to the energy accumulated in the reactances L1 and L2 is output to the output side, and the output rectifying diode D
It is rectified by 1 and D2, and is smoothed by the reactance L4 and the electrolytic capacitor C2 for smoothing the output to become an output having the output voltage Vout. Where reactance L
Reference numeral 4 serves to smooth the rush current flowing into the electrolytic capacitor C2 and suppress its peak value.

Now, the adder circuit 2 includes a switching element Q.
A PWM signal P3 for turning on / off 3 is output.
The PWM signal P3 is generated from the PWM signals P1 and P2 as a signal that turns on the switching element Q3 when either the switching element Q1 or the switching element Q2 is turned on. Specifically, the PWM signal P3 can be generated by performing a logical OR negation (NOR) operation on the PWM signal P1 and the PWM signal P2 output by the PWM control unit 1.

The pulse generated by turning on / off the switching element Q3 from the input voltage Vin is
Smoothed by electrolytic capacitor C1 and reactance L3,
It is supplied to the center tap of the transformer T1. Here, in such a switching power supply device, the relationship between the duty ratio of the PWM signal P1 and the PWM signal P2 output by the PWM control unit 1 and the effective voltage Vc supplied to the center tap of the transformer T1 is the input voltage Vin. As a constant,
It is represented as shown in Figure 2a.

That is, the magnitude of the voltage Vc supplied to the center tap of the transformer T1 depends on the switching element Q3.
As the duty ratio of the PWM signal P1 and the PWM signal P2 output from the PWM control unit 1 decreases, the duty ratio decreases as the duty ratio of the PWM signal P1 decreases.

Therefore, when the input voltage Vin fluctuates and increases, in order to maintain the output voltage Vout at the target voltage, the PWM signals P1, P are controlled by the PWM controller 1.
2 is controlled so that the pulse width of the PWM signal P3 becomes smaller and the pulse width of the PWM signal P3 also becomes smaller.
The voltage Vc supplied to the first center tap is controlled to be small. Therefore, the pulse width of the PWM signals P1 and P2 at which the output voltage Vout reaches the target voltage can be made larger than that in the case where the input voltage Vin is directly supplied to the center tap of the transformer T1. As a result, the peak value of the current flowing through the switching elements Q1 and Q2 and the inrush current value of the output smoothing capacitor C2 are determined by the input voltage Vi.
Compared with the case where n is directly supplied to the center tap of the transformer T1, it is suppressed to be small.

2b-1 and 2b show the case where the input voltage Vin is directly supplied to the center tap of the transformer T1 (b-
1) and the switching element Q in the configuration of the present embodiment
When the voltage supplied to the center tap of the transformer T1 is controlled by 3 (b-2), the switching element Q1,
The current IQ flowing through Q2 is shown under the same input voltage, same target voltage, and same load conditions.

As shown in the figure, according to the configuration of this embodiment, the pulse widths of the PWM signals P1 and P2 are equal to the input voltage Vi.
Compared with the case where n is directly supplied to the center tap of the transformer T1, the current IQ flowing through the switching elements Q1 and Q2 is suppressed to be small. Each peak of the current IQ represents the current flowing through the switching element Q1 and the current flowing through the switching element Q2 alternately. In the figure, the AC component is shown as the supply voltage Vc of the center tap of the transformer T1.

The embodiments of the present invention have been described above. The configuration of performing PWM control of the voltage supplied to the center tap of the transformer T1 in the present embodiment is similarly applied to the control of the voltage supplied to the center tap of the transformer T2 in the configuration using the insulating transformer T2 shown in FIG. Can be applied.

In the above, the PWM signal P3 for controlling the voltage supplied to the center tap of the transformer T1 is set to PW.
From the M signal P1 and the PWM signal P2, the switching element Q
When either 1 or the switching element Q2 is on, it is generated as a signal for turning on the switching element Q3.
When the output voltage Vout is larger than the target voltage, the PWM signal P3 has a smaller pulse width (duty ratio) following the absolute value of the difference, and the output voltage Vou is smaller than the target voltage.
It suffices that the pulse width (duty ratio) increases in accordance with the absolute value of the difference when t is small.

As described above, according to this embodiment, the peak current can be suppressed by setting the voltage supplied to the center tap of the transformer T1 as the target of the PWM control.

[0027]

As described above, according to the present invention, the PWM
The peak current can be suppressed in the switching power supply device that controls the output voltage by control.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a relationship between a PWM signal and a supply voltage and an operation example of the switching power supply device according to the embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of a conventional switching power supply device.

FIG. 4 is a circuit diagram showing a configuration of a conventional switching power supply device.

[Explanation of symbols]

1: PWM control unit, 2: addition circuit, C1, C2, C3:
Electrolytic capacitors, D1, D2: Diodes, L1, L
2, L3, L4: reactance, Q1, Q2, Q3: switching element, R1, R2: resistor, T1: non-insulating transformer, T2: insulating transformer.

Claims (4)

[Claims] 1. A PWM (Pulse Width Modulat) input voltage is used.
ion) control for converting the output voltage to an output voltage, the transformer, a transformer for transforming the input voltage to supply the transformer as a supply voltage, and turning on a current flowing through the transformer by the supply voltage. A first switching element that is turned on / off, a rectifying / smoothing circuit that rectifies and smoothes an output current of the transformer into an output voltage, and the first switching element so that there is no difference between the output voltage and a predetermined target voltage. And a supply voltage control circuit for performing PWM control of ON / OFF of the transformer, the transformer means includes a second switching element provided between the application point of the input voltage and the transformer, A smoothing circuit for smoothing the voltage supplied from the power source of the input voltage through the second switch and supplying the smoothed voltage to the transformer as the supply voltage. , The supply voltage control circuit, the on / off the second switching element, PWM by the PWM signal whose duty ratio decreases as the output voltage is greater than the target voltage
A switching power supply device characterized by being controlled. 2. An input voltage is PWM (Pulse Width Modulat)
ion) control is used to convert the output voltage to an output voltage, the transformer having an intermediate tap, a transformer for transforming the input voltage and supplying it to the intermediate tap of the transformer as a supply voltage, A first switching element arranged between the one end and the ground potential, and a second switching element arranged between the second end of the transformer and the ground potential,
A rectifying / smoothing circuit that rectifies and smoothes an output current of the transformer to obtain the output voltage, and turns on / off the first switching element and the second switching element so that a difference between the output voltage and a predetermined target voltage is eliminated. PWM to control the ON / OFF of the switching element of the
A power supply for the input voltage; and a third switching element provided between the application point of the input voltage and the intermediate tap of the transformer, and a power supply for the input voltage. A smoothing circuit that smoothes a voltage supplied through the third switch and supplies the smoothed voltage to the intermediate tap of the transformer as the supply voltage, wherein the supply voltage control circuit turns on / off the third switching element. A switching power supply device, wherein OFF is PWM-controlled by an input voltage transforming PWM signal having a smaller duty ratio as the output voltage is higher than the target voltage. 3. An input voltage is PWM (Pulse Width Modulat).
ion) control for converting into an output voltage, which is a non-isolated transformer having an intermediate tap, and a transformer that transforms the input voltage and supplies it as a supply voltage to the intermediate tap of the non-insulated transformer. A first switching element arranged between the first end of the non-insulated transformer and the ground potential, and a second switching element arranged between the second end of the non-insulated transformer and the ground potential. A switching element and a rectifying / smoothing circuit connected between both ends of the non-insulating transformer to rectify and smooth the current input from the non-insulating transformer to obtain the output voltage; and the output voltage and a predetermined target voltage. The ON / OFF of the first switching element and the ON / OFF of the second switching element are mutually switched so that there is no difference between the output voltage and the predetermined target voltage. And a supply voltage control circuit for performing PWM control in a phase shifted by a half cycle, and the transformer means is provided between the application point of the input voltage and the intermediate tap of the non-insulated transformer. A third switching element, and a smoothing circuit that smoothes a voltage supplied from the power source of the input voltage via the third switch and supplies the smoothed voltage to the intermediate tap of the non-insulated transformer as the supply voltage. The supply voltage control circuit PWM-controls ON / OFF of the third switching element by an input voltage transformation PWM signal having a smaller duty ratio as the output voltage is higher than the target voltage. Switching power supply. 4. The switching power supply device according to claim 2, wherein the PWM control section includes a first output voltage control PWM signal for controlling an ON period of the first switching element, and And a second output voltage control PWM signal for controlling the ON period of the second switching element, the supply voltage control circuit, and the first output voltage control PWM
The input voltage transformation PWM that turns on the third switching element during the on period of the first switching element and the on period of the second switching element based on the signal and the second output voltage control PWM signal. A switching power supply device characterized by generating a signal.