JP2976603B2 - Series resonant converter control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control circuit for a series resonant converter which performs a push-pull operation, and more particularly to a control circuit for a series resonant converter which limits an output capacity according to a change in an input power supply voltage.

[0002]

2. Description of the Related Art An example of a conventional push-pull type series resonant converter will be described with reference to FIG. In FIG. 3, 1
Is an inverter transformer, the positive terminal of the DC input power supply 2 is connected to the middle point of the primary winding of the inverter transformer 1, and one end of the primary winding of the inverter transformer 1 is connected to the collector of the transistor switch 3. , Its emitter is connected to the negative pole of the DC input power supply 2. A diode 5 is connected in parallel between the collector and the emitter of the transistor switch 3. In addition, 1 of the inverter transformer 1
A parallel connection circuit of a transistor switch 4 and a diode 6 is similarly connected between the other end of the next winding and the negative electrode of the DC input power supply 2.
The transistor switches 3 and 4 are turned on and off alternately by a control signal input complementarily to the base of the transistor 4.

Then, a current flows through a series resonance circuit composed of an inductance 7 and a capacitor 8 connected in series to the secondary side of the inverter transformer 1, is rectified by the full-wave rectification circuit 9, and is smoothed by the smoothing circuit 10. A current (output current) I _O flows to the load 11. Then, the output of the output current detector 12 connected in series to the load 11 is input to the error amplifier 14. The error amplifier 14 compares and amplifies the output voltage of the output current detector 12 with the reference voltage 16 and supplies the amplified voltage to the voltage / frequency converter 18. This voltage
The frequency converter 18 oscillates with a rectangular wave having a frequency corresponding to the input voltage. The two-phase dividing circuit 19 outputs two control signals a and b having phases different from each other by 180 ° in accordance with the cycle of the voltage / frequency converter 18, and outputs the two control signals a and b.
4 is input to each base.

The above-described series resonant converter has an output current I
_{When O} becomes larger than the set value, the output voltage of the error amplifier 14 decreases and the oscillation frequency of the voltage / frequency converter 18 decreases, so that the on / off cycle of the transistor switches 3 and 4 becomes longer, and the output current increases. acts to reduce the I _O, output current I _O conversely becomes smaller than the set value, it acts to increase the output current I _O is higher the oscillation frequency of the voltage-frequency converter 18. As a result, the output current I _O is controlled to have a constant value.

FIGS. 4 and 5 are characteristic diagrams of the output current used to explain the operation of FIG. 3. FIG. 4 shows the uncontrolled operation when the voltage of the DC input power supply 2 fluctuates when the output voltage of the error amplifier 14 is maximum. FIG. 5 shows a characteristic in which the output current _IO is controlled to be constant. 4 and 5, c indicates a voltage of the DC input power supply 2 of 53 V, d indicates a voltage of the DC input power supply 2 of 48 V, and e indicates a voltage of the DC input power supply 2 of 4 V.
The output current characteristic at 2 V is shown.

Here, in the above-described series resonance converter, the output voltage detector 13 connected in parallel to the load 11
And the reference voltage 17 are compared and amplified by the error amplifier 15, and the signal is added to the output of the error amplifier 14 via the diode 20. As a result, as shown in FIG. 5, the voltage applied to the load 11 is controlled so as to be forcibly drooped when the voltage exceeds the voltage V _O.

[0007]

In the case of the voltage limiting circuit in the conventional series resonant converter, when the DC input voltage is high due to a delay in the response of the output voltage detector under a situation where the load changes suddenly. 4A or 4B, that is, a point at which the series resonant converter has the maximum power. At this time, there is a problem that the inverter transformer is demagnetized due to the saturation voltage of the pair of transistor switches and the variation in wiring, and the pair of transistor switches may be damaged.

[0008]

A series resonance converter control circuit according to the present invention comprises an inverter transformer connected to a DC input power supply, and a series resonance circuit and a full-wave rectification circuit connected to the secondary side of the inverter transformer. A connection circuit, an output current detector that detects a current supplied to a load from an output of the full-wave rectifier circuit through a smoothing circuit, and amplifies a difference between an output of the output current detector and a first reference voltage. A first error amplifier, a voltage / frequency converter for converting an output voltage of the first error amplifier into a corresponding frequency,
A two-phase dividing circuit for dividing the output waveform of the frequency converter to generate two control signals having a phase difference of 180 ° from each other, and two transistor switches for turning on / off the input of the inverter transformer by the control signal With
In a series resonance converter in which the output current is controlled by changing the output frequency of the voltage / frequency converter in accordance with the magnitude of the output current, the difference between the signal from the DC input power supply and a second reference voltage is calculated. The output of the second error amplifier to be amplified is connected to the output of the first error amplifier via a diode.

[0009]

According to the present invention, the error comparison signal of the fluctuation of the input power supply voltage is incorporated in the constant current control, and it is possible to prevent the inverter transformer from being demagnetized by passing the point where the maximum power is transiently applied to the load that changes rapidly. To prevent.

[0010]

FIG. 1 is a block diagram showing one embodiment of a series resonance converter control circuit according to the present invention. In FIG. 1, the same reference numerals as in FIG. 3 denote corresponding parts, and reference numeral 20 denotes an error amplifier for amplifying the difference between the signal from the DC input power supply 2 and the reference voltage 21. The output of the error amplifier 20 is a diode 22. The output is connected to the output of the error amplifier 14 via the output terminal.

Then, diodes 5 and 6 are connected in parallel between the collectors and emitters of the transistor switches 3 and 4, respectively.
, And the collectors are connected to both ends of the primary winding of the inverter transformer 1 connected to the DC input power supply 2 respectively. The positive terminal of the DC input power supply 2 is connected to the middle point of the primary winding of the inverter transformer 1. One end of a secondary winding of the inverter transformer 1 is connected to a series resonance circuit including an inductance 7 and a capacitor 8, and a full-wave rectifier circuit 9 is provided between the other end of the secondary winding of the inverter transformer 1 and the capacitor 8. The output side of the series connection circuit of the series resonance circuit and the full-wave rectification circuit 9 connected to the secondary side of the inverter transformer 1 is connected to the load 11 via the smoothing circuit 10.

An output current detector 12 for detecting a current supplied to a load 11 from an output of the full-wave rectifier circuit 9 via a smoothing circuit 10, and an output of the output current detector 12 and a reference voltage 16. An error amplifier 14 for amplifying the difference, a voltage / frequency converter 18 for converting an output voltage of the error amplifier 14 into a corresponding frequency, and a voltage / frequency converter 1
8 output waveforms divided by 180.degree.
A two-phase dividing circuit 19 for generating two control signals a and b, and two transistor switches 3 and 4 for turning on and off the input of the inverter transformer 1 by the control signals a and b, respectively. The output current is controlled by changing the output frequency of the voltage / frequency converter 18 in accordance with the above.

FIG. 2 is a characteristic diagram showing an output current characteristic used for explaining the operation of FIG.
V and d indicate the respective output current characteristics when the voltage of the DC input power supply 2 is 48 V, and e indicates the output current characteristics when the voltage of the DC input power supply 2 is 42 V.

Next, the operation of the embodiment shown in FIG. 1 will be described with reference to FIG. First, the output of the output current detector 12 connected in series to the load 11 is compared and amplified with the reference voltage 16 by the error amplifier 14 and input to the voltage / frequency converter 18. The voltage / frequency converter 18 oscillates with a rectangular wave having a frequency corresponding to the input voltage. Then, the two-phase dividing circuit 19 outputs one signal every period of the voltage / frequency converter 18.
Outputting two control signals a and b different in phase by 80 °,
The transistor switches 3 and 4 are turned on and off. The output current becomes constant by a series of these operations and the feedback action.

Next, in this embodiment, the DC input power supply 2
The difference between the signal from the amplifier and the reference voltage 21 is compared and amplified by the error amplifier 20, and the output signal is connected to the output of the error amplifier 14 via the diode 22. Thereby, when the input voltage increases, the output of the error amplifier 20 decreases, and the output of the error amplifier 14 is forcibly reduced via the diode 22. For this reason, the current-voltage characteristics of the series resonant converter with respect to the fluctuation of the DC input voltage are as shown in FIG. 2 showing the output current characteristics in the case of the present invention.

[0016]

As described above, according to the present invention, in the control circuit of the series resonance converter, the error comparison signal of the fluctuation of the input power supply voltage is incorporated in the constant current control, and the maximum power is transiently applied to a suddenly changing load. Since the inverter transformer is prevented from being demagnetized by passing through the point, it is possible to avoid the transient passage of the maximum power point which has conventionally caused the inverter transformer to be demagnetized due to a suddenly changing load. It has the effect of.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a series resonance converter control circuit according to the present invention.

FIG. 2 is a characteristic diagram showing output current characteristics used for explaining the operation of FIG. 1;

FIG. 3 is a block diagram showing an example of a conventional series resonance converter.

FIG. 4 is a characteristic diagram showing non-control characteristics when the DC input voltage varies for the explanation of the operation in FIG. 3;

FIG. 5 is a characteristic diagram showing a state in which the output current used for explaining the operation of FIG. 3 is controlled to be constant.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inverter transformer 2 DC input power supply 3, 4 Transistor switch 7 Inductance 8 Capacitor 9 Full-wave rectifier circuit 10 Smoothing circuit 11 Load 12 Output current detector 14 Error amplifier 16 Reference voltage 18 Voltage / frequency converter 19 Two-phase split circuit 20 Error Amplifier 21 Reference voltage 22 Diode

Claims (1)

(57) [Claims] 1. An inverter transformer connected to a DC input power supply, a series connection circuit of a series resonance circuit and a full-wave rectifier circuit connected to a secondary side of the inverter transformer, and a smoothing circuit based on an output of the full-wave rectifier circuit. , An output current detector for detecting a current supplied to a load, a first error amplifier for amplifying a difference between an output of the output current detector and a first reference voltage, and the first error amplifier A voltage-frequency converter for converting the output voltage of the voltage-frequency converter into a corresponding frequency, and a two-phase dividing circuit for dividing the output waveform of the voltage-frequency converter to generate two control signals having phases different from each other by 180 °. And two transistor switches for turning on and off the input of the inverter transformer according to the control signal, and changing the output frequency of the voltage / frequency converter according to the magnitude of the output current. The output of the second error amplifier, which amplifies the difference between the signal from the DC input power supply and the second reference voltage, is output via the diode to the first error amplifier A series resonance converter control circuit, wherein the control circuit is connected to an output of the converter.