JPH08242579A - Switching power supply circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] A switching power supply circuit in which the resonance frequency of the voltage resonance and the current resonance, that is, the time constant in the push-pull switching power supply is determined by a common resonance inductor, can easily realize the change of the resonance frequency. provide. [Configuration] Switch element (1, 2) that performs push-pull operation
After the secondary side output current of the transformer 5 that is input according to the on / off operation of the current resonance is caused by the series resonance of the combined inductance of the resonance inductor (14, 15) and the leakage inductance of the transformer 5 and the current resonance capacitor 3, the rectifier diode The smoothing capacitor 10 is charged through the choke coil 9 with the direct current obtained as a result of rectification by (7, 8). In addition, the self-inductance of the transformer 5 and the resonance inductor (14, 15) while the two switch elements (1, 2) are off.
Voltage resonance is caused by parallel resonance between the combined inductance of the switch and the stray capacitance of the switch element (1, 2).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a push-pull type switching power supply circuit, and more specifically, it utilizes voltage resonance and current resonance to significantly reduce switching loss to improve conversion efficiency and to improve conversion efficiency. The present invention relates to a switching power supply circuit in which the current operation waveform of is closer to a sine wave to reduce noise.

[0002]

2. Description of the Related Art Generally, there is a power supply using resonance as a highly efficient power supply among switching power supplies. Among them, particularly for high output, there is a push-pull type resonance power source using a switching element that alternately turns on and off two switching elements.

A push-pull type resonance type power source, which is one type of conventional switching power source, will be described below.

FIG. 5 is a block diagram of a resonance type power source which is a kind of conventional switching power source. In FIG. 5, 1 and 2 are switching elements 1 and 2, which are alternately turned on and off, 3 are capacitors for current resonance, 4 is a DC power source for supplying energy to the switching elements 1 and 2, and 5 is AC output from the switching elements. A transformer that outputs a signal to the secondary side, 7 and 8 are rectifier diodes that convert an AC signal output from the transformer 5 into a direct current, 9 is a choke coil, and 10 is a smoothing capacitor that smoothes the output signal of the choke coil 9, 11 Is a load, and 12 and 13 are voltage resonance capacitors for resonating the voltage applied to the switch elements 1 and 2.

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

First, when the switching elements 1 and 2 are alternately turned on and off, the output voltage of each switching element, that is, the input voltage to the transformer 5 is an AC voltage having a peak value which is almost twice the voltage of the DC power supply 4. The current input to the transformer 5, after being rectified by the rectifier diodes 7 and 8 at the secondary side terminal, is input to the current resonance capacitor 3 and the choke coil 9. Here, since the impedance of the choke coil 9 is sufficiently high, the current input to the current resonance capacitor 3 undergoes current resonance due to series resonance between the leakage inductance L4 of the transformer 5 and the current resonance capacitor 3, and the resulting resonance current. Is smoothed by the choke coil 9 and the smoothing capacitor 10 and sent to the load 11. While the switching element 1 is turned on, this resonance current half-wave passes and the rectifier diode 7 is reverse-biased and turned off when the direction of the current is reversed, so that the series resonance is stopped. That is, the resonance automatically stops when the resonance current ends in half wave and the current returns to zero. After the resonance current becomes zero, switch element 1
If you keep turning on, nothing happens, but since it is inefficient because the time for which energy is not transmitted becomes long, it is sufficient to turn it off with some margin. Further, since the resonance time by the leakage inductance L4 and the current resonance capacitor 3 is constant, the ON time of the switch element 1 may be a constant value.

Next, when the switch element 1 is turned off, that is, when the two switch elements are both turned off, the transformer 5 is turned off.
The current of the secondary side terminal becomes zero, and the voltage of the switch element 1 becomes the self-inductance of the transformer 5 and the voltage resonance capacitor 1.
The voltage starts to increase with a constant time constant due to parallel resonance with 2, and is maintained at a voltage value twice that of the DC power supply 4. When the switch element 2 is turned on at that timing, a resonance current in the opposite direction to the above starts to flow to the secondary side. The voltage resonance and the current resonance are alternately generated by the above operation, and the voltage and the current in the circuit are made into the resonance waveform, so that the voltage applied to the switch element and the harmonic component contained in the current can be reduced. It is possible to reduce the loss when the current is turned on and off.

[0008]

However, in the above switching power supply circuit, it is necessary to set the time constants of the voltage and current resonances individually, and especially when used in audio equipment, radiation is radiated from the switch element, transformer and diode. In order to avoid reception interference such as AM tuners caused by unnecessary radiated noise, it is necessary to change the once determined switching frequency so that it does not affect the station frequency emitted from the broadcasting station. Correspondingly, there is a drawback that each resonance frequency must be adjusted individually. Specifically, it was necessary to replace the voltage resonance capacitor and the current resonance capacitor with those having different constants.

The present invention solves the above-mentioned conventional problems, and provides a switching power supply circuit in which components for resonance of voltage and current are shared and the resonance frequency can be easily changed or adjusted. The purpose is to do.

[0010]

In order to achieve this object, a switching power supply circuit of the first invention comprises a DC power supply,
The output signal of the DC power supply is alternately turned on and off to be converted into an AC signal, and two switch elements having a stray capacitance and the output of the DC power supply are connected to the center tap to electrically insulate the AC signal and A transformer that outputs to the side terminal, a rectifying unit that full-wave rectifies the output signal on the secondary side, a current resonance capacitor that is connected to the output terminal of the rectification unit, and a resonance inductor that is connected in series at both ends of the transformer, It is composed of a choke coil and a smoothing capacitor for smoothing the full-wave rectified signal.

The switching power supply circuit of the second invention is a DC power supply, two switch elements for alternately turning on and off the output signal of the DC power supply to convert it into an AC signal, and the output of the DC power supply at a midpoint tap. A transformer connected to electrically insulate an AC signal and output to the secondary side terminal, at least one or more resonance capacitors connected in parallel to the primary winding of the transformer, and both ends of the two switch elements respectively. The reverse conducting diode is connected, the rectifying unit is connected to the secondary side terminal, and the smoothing capacitor that smoothes the output signal of the rectifying unit.

[0012]

In the switching power supply circuit according to the first aspect of the invention described above, when the first and second switching elements are alternately turned on and off repeatedly, the rectifier diode forwards the current sequentially output from the secondary side of the transformer. Since it is biased to, the smoothing capacitor is charged through the choke coil after being rectified by the rectifying diode. At this time, in order to set the leakage inductance of the transformer and the inductance of the resonance inductor sufficiently smaller than the inductance of the choke coil, a sinusoidal resonance current is generated due to the series resonance of the combined inductance of the leakage inductance L4 of the transformer and the resonance inductor and the current resonance capacitor. Flows. When the half-wave of the resonance current has passed, the polarity of the current tends to be inverted, so that the rectifier diode is reverse-biased and the resonance current becomes zero. By turning off the switch element at this timing, the resonance current can be turned off in the zero state.

On the other hand, when both the first and second switch elements are off, the voltage applied to the switch element is the combined inductance of the self-inductance and the resonant inductor on the transformer primary side and the combined stray of the switch element and the transformer primary side. Due to the parallel resonance with the capacitor, the DC voltage value doubles or decreases to a zero voltage value with a gradient having a constant time constant, so that the resonance voltage can be turned off in a zero state.
Since the resonance inductor that determines the resonance frequency of these voltage resonance and current resonance is shared, it is possible to adjust by changing only the resonance inductor when changing the voltage and current resonance frequency. Adjustment becomes easy.

In the switching power supply circuit of the second invention, when the first and second switch elements are alternately turned on and off repeatedly, the current output to the secondary side is the leakage inductance L4 of the resonance capacitor and the transformer. A resonance waveform is generated by series resonance with. At the timing when the half wave of the resonance waveform has passed and it returns to zero again, the reverse conducting diode turns on and a current of reverse polarity flows. The resonance current can be turned off in the zero state by turning off the switch element at the timing when the reverse current returns to zero again.

On the other hand, when both the first and second switch elements are off, the voltage applied to the switch elements is doubled with a gradient having a constant time constant due to parallel resonance between the self-inductance on the transformer primary side and the resonance capacitor. Therefore, the resonance voltage can be turned off in the state of zero because it increases to the DC voltage value or decreases to the zero voltage value. Since the resonance capacitor that determines the resonance frequency of the voltage resonance and current resonance is shared, adjustment can be made by changing the resonance capacitor when changing the voltage and current resonance frequencies. Will be easier.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram of a switching power supply circuit in an embodiment of the first invention, and FIG. 3 shows operation timings and operation waveforms of respective parts.

In FIG. 1, 14 is a characteristic component.
Reference numerals 15 and 15 are resonance inductors for performing voltage resonance with the stray capacitances of the switch elements 1 and 2 and current resonance with the current resonance capacitor. Others are the same as in the conventional configuration.

The operation of the switching power supply circuit of this embodiment constructed as above will be described below.

First, the switch elements 1 and 2 are respectively shown in FIG.
When the gate voltage is repeatedly turned on and off at the timings of (g) and (h), the voltage value applied to the switch elements 1 and 2 is the voltage V _i of the DC power supply 4 as shown in FIGS. 3 (a) and 3 (b).
The current generated from the primary side of the transformer 5 is sequentially input to the rectifying diodes 7 and 8 via the transformer 5 when any one of the switch elements is turned on. The DC current sequentially output from the rectifying diodes 7 and 8 is sequentially input to the current resonance capacitor 3 and the choke coil 9. At this time, when the load 11 is not connected, that is, when there is no load, the currents i _S1 and i _S2 generated from the primary side of the transformer 5 are only the excitation current waveforms shown by the dotted lines in FIGS. 3 (c) and 3 (d). Become. Further, the current input to the choke coil 9 is smoothed by the smoothing capacitor 10. Here, when the switch element 1 is on, that is, while S1 is high, the rectifier diode 7 is forward biased, so that the charge current flows into the smoothing capacitor 10. 1 and the impedance of the rectifying diode 7 are sufficiently small, the choke coil 9
The inductance of the choke coil 9 must be set sufficiently high by setting it as the leakage inductance of the transformer 5 and the inductance of the resonance inductor. And the inductance of the resonance inductors 14 and 15 is 5 [μH].
Is set to. Further, generally, the leakage inductance of the transformer is about the same as the above value, and it is necessary to pay particular attention to the setting of the resonance inductors 14 and 15.

Under the conditions as described above, the current on the secondary side is the combined inductance of the leakage inductance (that is, L4) of the transformer 5 and the resonance inductor 14 and the current resonance capacitor 3 while the switch element 1 is on. It becomes a series resonance current. The resonance current i _L1 on the secondary side when the load 11 is connected at this time has a waveform as shown in FIG. 3 (e), and the current i _S1 on the primary side has a waveform as shown by the solid line in FIG. 3 (c). Becomes As shown in FIGS. 3 (e) and 3 (f), the secondary side resonance current becomes a reverse bias when the half-wave passes and the direction of the current is reversed, so that the rectifier diode 7 is reverse biased and is turned off. . That is, the resonance automatically stops when the resonance current ends in half wave and the current becomes zero. Therefore, in order to end the resonance at zero current, it is necessary to keep the switch element 1 ON until the resonance current returns to zero.

Next, when the switch element 1 is turned off, the transformer 5 operates by parallel resonance of the combined inductance of the self-inductance of the transformer 5 and the resonance inductor 14 and the stray capacitance of the switch element 1, as shown in FIG. The voltage waveform has a slope at the rising edge, and the period of this slope is the parallel resonance period. Further, when the charge continues and the voltage value V _S1 rises to become almost the same value as + 2V _i , the parallel resonance ends.

On the other hand, at the timing when the switch element 1 is turned off, the primary side current i _S1 flows in the positive direction due to the parallel resonance of the combined inductance of the self-inductance of the transformer 5 and the resonance inductor 14 and the stray capacitance of the switch element 1. The charges charged in the element 2 are discharged and the voltage value V _S2 of the switch element 2 is shown in FIG.
It descends with an inclination as shown in (b). The slope at this time causes parallel resonance with the time constant of the combined inductance of the self-inductance of the transformer 5 and the resonance inductor and the stray capacitance of the switch element 2 as in the case of charging. When the discharge ends and the parallel resonance also ends, and the switch element 2 is turned on next, that is, when S2 in FIG. 3 (h) becomes high, the primary side current i _S2 starts to flow in the forward direction and from the secondary side of the transformer 5. The output current i _L2 passes through the rectifying diode 8 and then is charged into the smoothing capacitor 10 via the choke coil 9 and the combined inductance of the resonance inductor 15 and the leakage inductance L4 of the transformer and the series resonance of the current resonance capacitor 3 are generated. Due to the current resonance, i _L2 as shown in FIG. 3 (f) is obtained.

By repeating the above operation, the switch elements 1 and 2 perform the push-pull operation to drive the transformer 5. Therefore, the current on the secondary side output via the transformer 5 is rectified by the rectifying diodes 7 and 8 and further charged into the smoothing capacitor 10 through the choke coil 9. At this time, the inductance of the choke coil 9 >> is set so that the leakage inductance of the transformer 5 and the inductances of the resonance inductors 14 and 15 are set, so that the combined inductance of the resonance inductors 14 and 15 and the leakage inductance L4 of the transformer 5 and the current resonance. Due to series resonance with the capacitor 3, a resonance current is output from the secondary side of the transformer 5.

It is preferable to use MOS-FETs for the switch elements 1 and 2 because the loss of the elements themselves is small and they are easy to drive.

As described above, according to the embodiment of the first invention, voltage resonance is caused by the stray capacitances of the two switch elements of the push-pull circuit, the self-inductance of the transformer, and the combined inductance of the resonance inductor, and further the transformer. In order to resonate the secondary side current, the series resonance is performed by the current resonance capacitor, the resonance inductor, and the combined inductance of the leakage inductance of the transformer. By performing these zero-voltage switching and zero-current switching, noise on spikes generated inside the circuit and harmonic components contained in the internal waveform can be reduced, and the problems of tuner interference and audio quality deterioration of audio equipment can be significantly reduced. it can.

Next, FIG. 2 shows a block diagram of a switching power supply circuit according to an embodiment of the second invention, and FIG. 4 shows operation timings and operation waveforms of respective parts.
In FIG. 2, as characteristic components, 16 and 17 are resonance capacitors for performing voltage and current resonance, 19 and 20 are reverse conducting diodes for passing currents of opposite polarities flowing through the switch elements 1 and 2, and 18 is a current. It is the leakage inductance included in the transformer 5 for performing resonance, and the rest is the same as the conventional configuration.

The operation of the switching power supply circuit of this embodiment having the above configuration will be described below.

First, the switch elements 1 and 2 are respectively shown in FIG.
When the gate voltage is repeatedly turned on and off at the timings (g) and (h), the voltage value applied to the switch elements 1 and 2 is the voltage Vi of the DC power supply 4 as shown in FIGS. 4 (a) and 4 (b).
The current generated from the primary side of the transformer 5 is sequentially input to the rectifying diodes 7 and 8 via the transformer 5 when any one of the switch elements is turned on. The DC current sequentially output from the rectifying diodes 7 and 8 is sequentially charged into the smoothing capacitor 10. At this time, if the load 11 is not connected, that is, in a no-load state, the transformer 5
The currents i _S1 and i _S2 generated from the primary side of the
Only the exciting current waveform shown by the dotted line in (d) is obtained. Here, when the switch element 1 is on, that is, while S1 is high, the rectifying diode 7 is forward biased, so that the charge current flows into the smoothing capacitor 10, but the primary side self-inductance of the transformer 5 >>> Leakage The inductance is set to be 18, and the values thereof are, for example, a primary-side self-inductance of 5 [mH] and a leakage inductance of 15 [μH]. It becomes a resonance current due to series resonance with.

At this time, the current i _S1 on the primary side when the load 11 is connected has a waveform as shown by the solid line in FIG.
The resonance current i _L1 on the secondary side has a waveform as shown in FIG. As shown in FIG. 4 (c), the primary side resonance current has a reverse conduction diode 1 when a half wave has passed and the current direction is reversed.
9 is turned on to release the energy of the resonance capacitor 16. Therefore, it is necessary to continue to turn on the switch element 1 until the primary resonance current is reversed and returns to zero again. Further, as shown in FIG. 4E, the secondary side resonance current does not flow in the reverse direction because the rectifier diode 7 is reverse biased and turns off when a half wave has passed and the direction of the current is reversed. After 7 is turned off, the rectifying diode 8 is turned on to discharge a reverse current.

Next, when the switch element 1 is turned off, the transformer 5 operates by parallel resonance of the self-inductance of the transformer 5 and the resonance capacitor 16, so that a voltage waveform having a rising slope as shown in FIG. The period of is the parallel resonance period. Further, charging continues and the voltage value V _S1 rises and the switch element 2 is turned on at the timing when it becomes almost the same value as + 2V _i , whereby parallel resonance ends and the voltage value applied to the switch element 1 is held at + 2V _i. . At this time, if the voltage continues to be turned off even after the voltage value becomes + 2V _i , a resonance waveform having a peak in the voltage value is generated and a large withstand voltage margin of the switch elements 1 and 2 is required. Attention must be paid to the setting of the on-timing of S2.

On the other hand, at the timing when the switch element 1 is turned off, the primary side current i _S1 flows in the positive direction due to the parallel resonance of the self-inductance of the transformer 5 and the resonance capacitor 16, so that the charge charged in the resonance capacitor 17 is discharged and the switch is switched. The voltage value V _S2 of the element 2 is shown in FIG.
It descends with an inclination as shown in (b). Similar to charging, the slope at this time causes parallel resonance with the time constant of the self-inductance of the transformer 5 and the resonance capacitor 17. When the discharge ends and the parallel resonance also ends, and then the switch element 2 turns on, that is, when S2 in FIG. 4 (h) becomes high, the primary side current i _S2 starts to flow in the forward direction and the transformer 5
The current i _L2 output from the secondary side of the rectifier diode 8 passes through the rectifier diode 8 and is charged in the smoothing capacitor 10. At this time, the primary side current becomes a resonance current as shown in FIG. 4 (d) because current resonance is caused by series resonance between the resonance capacitor 17 and the leakage inductance 18 of the transformer, as in the ON period of the switch 1, and becomes a secondary side current. _Yields i _L2 as shown in FIG.

By repeating the above operation, the switch elements 1 and 2 perform the push-pull operation to drive the transformer 5. Therefore, the secondary current output via the transformer 5 is rectified by the rectifying diodes 7 and 8 and then charged in the smoothing capacitor 10. At this time, since the self-inductance of the transformer 5 >> the leakage inductance 18, the primary side current becomes a direct current resonance between the resonance capacitors 16 and 17 and the leakage inductance L4 of the transformer 5 and has a resonance current waveform. When the value of the leakage inductance is extremely small in the design of the transformer, an inductor corresponding to L4 may be connected in series at both ends of the primary side of the transformer 5. In this case, the value of the connected inductor L4 is self-inductance >> L4. And need to. It is preferable to use MOS-FETs for the switch elements 1 and 2 because the loss of the elements themselves is small and they can be easily driven.

As described above, according to the second embodiment of the present invention, the self-inductance of the transformer and the resonant capacitor undergo voltage resonance by turning on / off the two switch elements of the push-pull circuit, and the leakage inductance of the transformer is further increased. By performing current resonance with the resonance capacitor, zero voltage switching and zero current switching on the primary side of the transformer are performed to reduce noise on spikes generated inside the circuit and harmonic components included in the internal waveform, and to resonate. 2 by installing a capacitor on the primary side
The current value can be reduced as compared with the case where it is arranged on the next side, and the stress on the capacitor can be reduced. Furthermore, since a resonance inductor is not required, there is no loss due to DC resistance and efficiency can be improved.

[0035]

As is apparent from the above description of the embodiments, the first aspect of the invention is that the secondary side output current of the transformer, which is input according to the on / off operation of the switch element that performs the push-pull operation, leaks between the resonance inductor and the transformer. A series resonance of a combined inductance with an inductance and a current resonance capacitor causes current resonance, and then a rectifying diode rectifies the resulting DC current to charge the smoothing capacitor via a choke coil. Further, while the two switch elements are off, voltage resonance is performed by parallel resonance between the combined inductance of the self-inductance of the transformer and the resonance inductor and the stray capacitance of the switch element. As a result, since the resonance inductor is shared by the voltage resonance and the current resonance, it is only necessary to change the inductance of the resonance inductor when changing the switching frequency in order to avoid reception interference such as AM tuner. It can be changed easily.

Further, by performing the voltage resonance operation and the current resonance operation at the timing at which they are alternately completed, a switching operation with extremely small loss can be realized, so that the problems of tuner interference and sound quality deterioration of audio equipment can be remarkably reduced. .

The second aspect of the present invention causes the primary side output current of the transformer, which is input according to the on / off operation of the switch element which performs the push-pull operation, to cause current resonance by series resonance of the resonance capacitor and the leakage inductance of the transformer,
The reverse conducting diode causes a current of opposite polarity to flow to release the energy of the resonant capacitor, and the secondary side rectifying diode rectifies the resulting direct current to charge the smoothing capacitor. Further, while the two switch elements are off, voltage resonance occurs due to parallel resonance of the self-inductance of the transformer and the resonance capacitor. As a result, the resonance capacitor is shared for the voltage resonance and the current resonance. Therefore, when the switching frequency is changed to avoid the reception interference of the AM tuner, it is only necessary to change the capacitance of the resonance capacitor, and the resonance frequency is easy. Can be changed to Furthermore, by performing the voltage resonance operation and the current resonance operation alternately at the timings at which they are completed, a switching operation with extremely low loss can be realized, so that the problems of tuner interference and audio quality deterioration of audio equipment can be significantly reduced. In addition, since the voltage and current resonance are performed on the primary side, when the secondary side output is increased, a resonance circuit and a choke coil for each output circuit unlike the conventional case are not required, and the entire circuit can be downsized. Can be achieved.

[Brief description of drawings]

FIG. 1 is a block diagram of a switching power supply circuit according to an embodiment of the first invention.

FIG. 2 is a block diagram of a switching power supply circuit according to an embodiment of the second invention.

FIG. 3 is a diagram showing operation waveforms of respective parts in the switching power supply circuit of the embodiment of the first invention.

FIG. 4 is a diagram showing operation waveforms of respective parts in the switching power supply circuit according to the embodiment of the second invention.

FIG. 5 is a block diagram showing a configuration of a conventional switching power supply circuit.

[Explanation of symbols]

 1, 2 Switch element 3 Current resonance capacitor 4 DC power supply 5 Transformer 7,8 Rectification diode 9 Choke coil 10 Smoothing capacitor 11 Load 12,13 Voltage resonance capacitor 14,15 Resonance inductor 16,17 Resonance capacitor 18 Leakage inductance 19,20 Reverse Continuity diode

Claims (4)

[Claims] 1. A direct current power source, two switch elements that alternately turn on and off the output signal of the direct current power source to convert it into an alternating current signal, and have stray capacitance, and the output of the direct current power source is connected to a midpoint tap. A transformer that electrically insulates the AC signal and outputs the AC signal to a secondary side terminal, a rectifying unit that performs full-wave rectification on the secondary side output signal, and a current resonance capacitor connected to an output terminal of the rectifying unit. A switching power supply circuit comprising a resonance inductor connected in series to both ends of the transformer, a choke coil for smoothing the full-wave rectified signal, and a smoothing capacitor. 2. The switching power supply circuit according to claim 1, wherein the inductance of the resonance inductor is smaller than the self-inductance of the transformer and the inductance of the choke coil. 3. A direct current power supply, two switch elements for alternately turning on and off the output signal of the direct current power supply to convert it into an alternating current signal, and the output of the direct current power supply is connected to a midpoint tap to electrically connect the alternating current signal. A transformer that is isolated from the output and outputs to the secondary side terminal, at least one capacitor that is connected in parallel to the primary winding of the transformer, and a reverse conducting diode that is connected to both ends of the two switch elements, respectively. A switching power supply circuit comprising: a rectifying unit connected to the secondary side terminal; and a smoothing capacitor that smoothes an output signal of the rectifying unit. 4. The switching power supply circuit according to claim 3, wherein the capacitance of the capacitor is larger than the stray capacitance included in the switch element.