JP2816892B2 - Resonant switching power supply - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonance type switching power supply used for a stabilized DC power supply or the like.

[Prior Art] At present, as a power supply for electronic communication used in a computer, a communication device and the like, a switching power supply of a PWM system having advantages of small size, measurement, and high efficiency is often used. However, when the switching frequency is 20 kHz or less, no major problem occurs.However, when the switching frequency is 50 kHz or more, switching at the time of switching on and off of the switching element due to the influence of leakage inductance of the power transmission transformer and stray capacitance of the switching element. The rate at which the voltage waveform and the current waveform at both ends of the element overlap increases, and a portion where the voltage and current waveforms overlap each other causes switching loss, and the loss increases as the oscillation frequency increases. When the switching loss increases, the power conversion efficiency decreases and heat is generated. Therefore, a large radiator is required, which hinders downsizing of the power supply device.

The above problem can be solved by the resonance type switching power supply device shown in FIG. The DC power supply circuit 1 of the resonance type switching power supply includes a power supply 2 and first and second terminals 3 and 4. Connected between the first terminal 3 and the second terminal 4 is a series circuit of first and second switching elements Q1 and Q2 composed of transistors, and a first and second resonance capacitor C1. , C2 are connected in series. A bypass diode D is connected to the first and second switching elements Q1 and Q2 which are alternately turned on and off.
1, D2 are connected in anti-parallel. Third and fourth diodes D3 and D4 are connected in parallel to the first and second resonance capacitors C1 and C2, respectively. First
And the connection midpoint 5 between the first and second resonance capacitors C1 and C2 and the first
A series circuit of a series resonance inductance element (reactor) L1 and the primary winding N1 of the transformer T is connected between the second switching element Q1 and the connection midpoint 6 of the second switching element Q2. That is, the resonance inductance element (reactor) L1
Is connected to a connection midpoint 5 between the first and second resonance capacitors C1 and C2, and the other end is connected to a connection midpoint 6 between the switching elements Q1 and Q2 via the primary winding N1. .

The transformer T functions as a part of an output circuit or a load circuit, and has secondary windings N2 and N3 in addition to the primary winding N1, and the secondary windings N2 and N3 having the center tap configuration. Is connected to a load 8 via an output rectifying / smoothing circuit 7 including diodes D5 and D6 and a smoothing capacitor C3.

A control circuit 9 for controlling on / off of the first and second switching elements Q1 and Q2 includes a voltage detection circuit 10 for detecting an output voltage of the output rectifying and smoothing circuit 7, and a voltage detection circuit
An error amplifier 12 for obtaining an output corresponding to the difference between the detection voltage obtained from the reference voltage source 10 and the reference voltage of the reference voltage source 11, and a VF (voltage) for outputting a frequency signal corresponding to the output voltage of the error amplifier 12 -Frequency) conversion circuit 13 and a switch control signal forming circuit 14 for alternately turning on and off the switching elements Q1 and Q2 at the output frequency of the VF conversion circuit 13.
Consisting of The switch control signal forming circuit 14 forms a control signal for the first switching element Q1 based on the output of the VF conversion circuit 13, and forms a control signal for the second switching element Q2 based on the inverted signal. The elements Q1 and Q2 are supplied to the base of the transistor.

The switching elements Q1 and Q2 are alternately turned on and off at a frequency lower than the resonance frequency of the series resonance circuit as shown in FIGS. First switching element
The period when Q1 is on and the second switching element Q2 is off (fifth
In (t1 to t4) of the drawing, first, a current I based on the series resonance of a circuit including the DC power supply 2, the first switching element Q1, the primary winding N1, the inductance element L1, and the second resonance capacitor C2 flows. . The voltage of the second resonance capacitor C2 is 0 V at time t1, as shown in FIG. 5C, but thereafter gradually increases to + E. When the voltage of the second resonance capacitor C2 becomes slightly higher than + E, the third diode D3 is turned on, and current flows therethrough. This prevents the capacitor C2 from being charged to a voltage higher than + E.

In the period from t2 to t3 in FIG.
, The positive current continues to flow through the switching element Q1 and the primary winding N1. Even when the discharge of the energy of the inductance element L1 ends at time t3 and the current 1 becomes zero, since the charging voltage of the capacitor C2 at this time is clamped at + E, the bypass diode D1 does not turn on. No current flows through the bypass diode D1. Therefore, even when the second switching element Q2 is turned on at the time point t4, the phenomenon that the accumulated carriers of the first bypass diode D1 flow through the second switching element Q2 does not occur. As a result, the loss when the second switching element Q2 is switched from off to on is reduced.

In a period from t4 to t7 when the second switching element Q2 is turned on, a series resonance circuit including the power supply 2, the first resonance capacitor C1, the inductance element L1, the primary winding N1, and the second switching element Q2 is formed. The power supply I is at t4 in FIG.
Flows as shown at ~ t7.

The output voltage of the output rectifying / smoothing circuit 7 is controlled by controlling the VF converter 13 with a voltage corresponding to the difference between the detection voltage obtained from the voltage detection circuit 10 and the reference voltage, and the first and second switching elements. This is done by changing the repetition frequency of Q1 and Q2 on / off. Changing the frequency changes the impedance of the circuit and the output voltage.

[Problems to be solved by the invention] By the way. In the conventional resonant switching power supply device shown in FIG. 4, the ON / OFF cycle of the first and second switching elements Q1, Q2, that is, the oscillation frequency changes by voltage control. The output current and the oscillation frequency have a proportional relationship, and when the load is light, the oscillation frequency falls within the audible frequency range,
May generate noise. In the conventional device, the VF
The converter 13 was required, and the apparatus was inevitably expensive.

Therefore, an object of the present invention is to provide a resonance type switching power supply device capable of driving at a constant frequency and reducing cost.

[Means for Solving the Problems] The present invention for achieving the above object is as follows. A current power supply circuit having a first terminal, a second terminal, and a third terminal for providing a midpoint potential between the first and second terminals; and between the first terminal and the second terminal. The first connected in series with each other
And a second switching element; and first and second resonance capacitors connected in series between the first terminal and the second terminal. A resonance inductance element having one end and the other end, wherein the one end is connected to a connection midpoint between the first and second resonance capacitors; and the other end of the inductance element and the first and second resonance capacitors. An output transformer or a load connected between the switching element and the connection middle point; and a bidirectional connection between the third terminal of the DC power supply circuit and the other end of the resonance inductance element. A switch and the first and second switching elements are alternately turned on and off, and the bidirectional switch is turned on with a phase difference with respect to the first and second switching elements. And a control circuit of the resonance type.

Note that the load can be connected via a transformer, a bidirectional switch can be connected to the intermediate terminal of the winding of the transformer, and the inductance of the transformer can be used for resonance.

Also, instead of the first and second resonance capacitors of the invention, a resonance capacitor can be connected between the third terminal of the DC power supply circuit and one end of the resonance inductance element.

[Operation] The bidirectional switch of the present invention has a function of flowing a current to the resonance inductance and the capacitor without substantially passing the load. As a result, it is possible to control the energy released to the load in the resonance operation, that is, to control the output voltage, and to control the voltage at a constant frequency.

First Embodiment Next, referring to FIGS. 1 and 2, a resonance type switching power supply device according to a first embodiment of the present invention, that is, a resonance type DC
-DC converter will be described. However, in FIG.
Parts that are substantially the same as those in the figure are given the same reference numerals, and descriptions thereof are omitted.

The resonant switching power supply of FIG. 1 includes a power supply circuit 1 having an intermediate tap or third terminal 20. Power supply circuit 1
Are first and second power supplies 2a, 2a respectively generating a voltage E / 2.
The third terminal 20 is connected in the middle of these series circuits. A bidirectional switch 22 is connected between the third terminal 20 and the right end 21 of the resonance inductance element L1 via a resonance current peak value adjustment inductance element (reactor) L2. The bidirectional switch 22 includes third and fourth switching elements Q3 and Q4 each including a transistor, and backflow prevention diodes D7 and D8.

The constant voltage control circuit 23 includes the voltage detection circuit 1 as in FIG.
0, includes a reference voltage source 11 and an error amplifier 12, and further includes a pulse generation circuit 24 and a phase control circuit 25.

The pulse generating circuit 24 generates two square-wave pulses shown in FIGS. 2A and 2B at a constant period T, and supplies them to the third and fourth switching elements Q3 and Q4. Give to. The phase control circuit 25 is shown in FIG.
The pulses of FIGS. 2C and 2D are generated by delaying the rising phase of the pulse of FIG. 2B by Td. The phase control circuit 25 controls the phase difference, that is, the delay time Td, in response to the output of the error amplifier 12 connected thereto. That is, the rising point of the pulse shown in FIGS. 2C and 2D is controlled so as to increase the phase difference Td when the voltage of the load 8 becomes higher than the reference. In this embodiment, a negative pulse corresponding to the phase difference Td is formed, and the negative pulse and the pulses shown in FIGS. A) get the pulse. Of course, the width of the negative pulse is controlled by the output of the error amplifier 12. The two output lines of the phase control circuit 25 are connected to the first and second switching elements Q1, Q2.

[Operation] The first resonance capacitor C1 is charged to the power supply voltage E,
When the third switching element Q3 is turned on by the control pulse of FIG. 2A at time t1 in FIG. 2 when the second resonance capacitor C2 is in the zero volt state, the power supply 2b and the third switching FIG. 2 (F) shows a series resonance circuit including the element Q3, the diode D7, the peak adjustment inductance element L2, the resonance inductance element L1, and the second resonance capacitor C2.
(2) starts flowing, and this current I2 gradually increases from t1 to t2. At the same time, since the second resonance capacitor C2 is charged, the voltage Vc2 gradually increases as shown in FIG. 2 (I).

As shown in FIG. 2 (C), when the first switching element Q1 is turned on at t2, the power supply 2a, the first switching element
As shown in FIG. 2 (G), the resonance power supply I starts to flow through the circuit composed of Q1, the primary winding N1, the resonance inductance element L1, the second resonance capacitor C2, and the power supply 2b. Therefore, the power supply to the transformer T to which the load 8 is connected is t1
Started with a delay of ~ t2. Since the current I flows through the primary winding N1 having a leakage inductance, it gradually increases from t2. On the other hand, when the first switching element Q1 is turned on, the third switching element Q3 is in a reverse bias state, and the current I2 decreases as shown in FIG. 2 (F) and becomes zero at t3. The current I1 flowing through the resonance inductance element L1 shown in FIG. 2 (H) is the sum of the current I2 shown in FIG. 2 (F) and the current I shown in FIG. 2 (G). It becomes a waveform and the resonance operation continues. Since the second resonance capacitor C2 is charged in advance with the current I2, the second resonance capacitor C2 is charged to the power supply voltage E in a relatively short time from the charging start point t2 by the current I passing through the transformer T. Second at t4
When the resonance capacitor C2 becomes the power supply voltage E, the third diode D3 is turned on.
The voltage Vc2 of C2 is clamped at E as shown in FIG. The energy stored in the resonance inductance element L1 is equal to that of the resonance inductance element L1 and the diode.
D3, the first switching element Q1, and the primary winding N1 are discharged by a circuit, and the discharge ends at t5.

The first and third switching elements Q1 and Q3 are on-controlled until t6, but since the second resonance capacitor C2 is charged to the power supply voltage E, the voltage of the primary winding N1 of the transformer T and The current is zero. Although the voltage waveform of the first resonance capacitor C1 is not shown in FIG. 2, this voltage waveform in the period from t1 to t7 is the same as the waveform in the period from t7 to t13 in FIG. 2 (I). That is, the voltage of the first resonance capacitor C1 is the power supply voltage E at t1, then discharges to zero at t4, and this zero state continues until t7. The discharge circuit of the first resonance capacitor C1 includes the first resonance capacitor C1,
A circuit including a power supply 2a, a third switching element Q3, a diode D7, and inductance elements L2 and L1, a first resonance capacitor C1, a first switching element Q1, a primary winding N1, and a resonance inductance element L1 It is a circuit consisting of

As shown in FIG. 2 (B), when the fourth switching element Q4 is turned on at t7, the power supply 2a and the first resonance capacitor
C1, resonance inductance element L1, peak adjustment inductance element L2, fourth switching element Q4 and diode D8, resonance operation, and second resonance capacitor C2, resonance inductance element L1, peak adjustment inductance Element L2, fourth switching element Q
4. A resonance operation is generated by a circuit including the diode D8 and the power supply 2b, and the voltage Vc2 of the second resonance capacitor C2 is equal to the second voltage.
As shown in FIG. 1 (I), the voltage gradually decreases and reaches zero volt at t10. The first resonance capacitor C1 during the period from t7 to t13
Is the same as that of the second resonance capacitor C2 during the period from t1 to t7. Currents I2, I, I1 during the period from t7 to t13
Is identical to that of the period t1 to t7 except that the polarity is opposite.

If the output voltage detection value by the voltage detection circuit 10 becomes higher than the reference value, for example, the output of the error amplifier 12 becomes higher, and the control of the first and second switching elements Q1, Q2 generated from the phase control circuit 25 is performed. The delay time Td of the rising phase of the pulse becomes longer. If the rise of the pulse is delayed as shown by the broken line in FIG. 2C, the currents I2 and I also change as shown by the broken lines in FIGS.
, The effective value of the current I flowing through the primary winding N1 decreases, the output voltage decreases, and returns to the reference value. In this voltage control, since the ON / OFF cycle of the first to fourth switching elements Q1 to Q4 is constant, it is possible to prevent the occurrence of noise due to the frequency change.

Second Embodiment Next, a description will be given of a resonant switching power supply according to a second embodiment shown in FIG. However, FIG. 3 and FIG.
In FIG. 7 and FIG. 7, the same parts as those in FIG. 1 and FIG.

In FIG. 3, the configuration is exactly the same as in FIG. 1, except that one resonance capacitor C1 is connected between the resonance inductance element L1 and the third terminal (intermediate terminal) 20 of the power supply circuit 1. Have been. In this case, the resonance capacitor C1
Charge and discharge between + E / 2 and −E / 2. That is, the capacitor
The voltage of C1 is set to the lowest level of the waveform of FIG.
2. Change the maximum level to + E / 2 and the middle to zero volts. First to fourth switching elements Q1 to Q4, current, I,
Changes in I1 and I2 are the same as in FIG.

The auxiliary resonance current I2 at the time of rising is determined by the resonance capacitor C1, the third switching element Q3, the diode D7, the peak adjustment inductance element L2, and the resonance inductance element L1.
The circuit or the resonance capacitor C1, the resonance inductance element L1, the peak adjustment inductance element L2, the fourth
Flows through a circuit including the switching element Q4 and the diode D8.

The current I is a circuit composed of a power supply 2a, a first switching element Q1, a primary winding N1, a resonance inductance element L1 and a resonance capacitor C1, or a power supply 2b, a resonance capacitor C1,
The current flows through a circuit including the resonance inductance element L1, the primary winding N1, and the fourth switching element Q4.

The resonance type switching power supply of FIG. 3 has the same effect as the apparatus of FIG.

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible.

(1) FE as the first to fourth switching elements Q1 to Q4
T (field effect transistor) can be used.
In the case of a common-source insulated gate FET, since a parasitic diode is included between the source and the drain, the bypass diodes D1 and D2 become unnecessary.

(2) The bidirectional switch including the third and fourth switching elements Q3 and Q4 can be replaced with one AC switching element.

(3) In FIGS. 2A and 2B, the widths of the control pulses of the third and fourth switching elements Q3 and Q4 are the first and second switching elements shown in FIGS. 2C and 2D. Q
1. Although it is longer than the pulse width of Q2, they may be the same as each other. Further, the width of the pulse shown in FIGS. 2A and 2B can be narrowed so as to be limited to the period for flowing the current I2 shown in FIG. 2F.

(4) In FIGS. 1 and 3, a load can be directly connected instead of the transformer T.

(5) As shown in FIGS. 6 and 7, the inductance of the transformer T may be used for resonance. That is, in FIGS. 6 and 7, an intermediate terminal 30 is provided on the primary winding N1 of the transformer T, and the peak adjusting inductance element L2 is connected to this. Since the inductance of the primary winding N1 of the transformer T is used as the resonance inductance, the resonance inductance element L1 shown in FIG. 1 is omitted. However, also in FIGS. 6 and 7, a resonance inductance element can be additionally provided. Since the auxiliary resonance current I2 does not flow through the entire primary winding N1, the contribution to the output voltage is smaller than the main resonance current I. Therefore, output voltage control becomes possible as in FIGS. 1 and 3.

(6) In FIGS. 1 and 3, a capacitor can be connected between the first and third terminals 3 and 20 and between the second and third terminals 4 and 20.

[Effects of the Invention] As is clear from the above, according to the present invention, it is possible to provide a resonance type switching power supply device capable of driving at a constant frequency with a relatively simple configuration.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a resonance type switching power supply according to a first embodiment of the present invention, FIG. 2 is a waveform diagram showing the state of each part in FIG. 1, and FIG. FIG. 4 is a circuit diagram illustrating a resonance type switching power supply device, FIG. 4 is a circuit diagram illustrating a conventional resonance type switching power supply device, FIG. 5 is a waveform diagram illustrating states of respective parts in FIG. 4, FIG. 6 and FIG. FIG. 7 is a circuit diagram illustrating a resonance type switching power supply device according to a modification. 1 DC power supply circuit 3 First terminal 4 Second terminal 20 Third terminal Q1 to Q4 Switching element C1, C2 Resonant capacitor L1 ... series resonance inductance element, N1 ... primary winding.

Claims (5)

(57) [Claims] A DC power supply circuit having a first terminal, a second terminal, and a third terminal for providing a midpoint potential between the first and second terminals; a first terminal and the second terminal; First and second switching elements connected in series between the first and second terminals, and first and second resonance elements connected in series between the first and second terminals. A resonance inductance element having one end and the other end, wherein the one end is connected to a connection midpoint between the first and second resonance capacitors; and a second end of the inductance element and the first end. And an output transformer or load connected between the connection point of the second switching element and a connection point between the third terminal of the DC power supply circuit and the other end of the resonance inductance element. Direction switch; the first and second switches And alternately on-off control of the device, and wherein the bidirectional switches the first and second
And a control circuit for performing on-control of each of the switching elements with a phase difference. 2. A DC power supply circuit having a first terminal, a second terminal, and a third terminal for providing a midpoint potential between the first and second terminals, a first terminal and the second terminal. First and second switching elements connected in series between the first and second terminals, and first and second resonance elements connected in series between the first terminal and the second terminal. And one end and the other end, wherein the one end is connected to a connection midpoint between the first and second resonance capacitors, and the other end is connected to the first and second switching elements. A winding connected to a point and having an intermediate terminal; a load receiving power supply based on the winding; and a load between the third terminal of the DC power supply circuit and an intermediate terminal of the winding. The connected bidirectional switch and the first and second switching elements are alternately turned on and off. Controlling, and said two-way switch first and second
And a control circuit for performing on-control of each of the switching elements with a phase difference. 3. A DC power supply circuit having a first terminal, a second terminal, and a third terminal for applying a midpoint potential between the first and second terminals, a first terminal and the second terminal. First and second switching elements connected in series with each other between the first and second terminals, and a resonance element connected between the connection midpoint between the first and second switching elements and the third terminal. A series circuit of a capacitor and a load or an output transformer, a resonance inductance element and a resonance capacitor, and both connected between a connection point between the resonance inductance element and the load or output transformer and the third terminal. Direction switch and the first and second switching elements are alternately turned on and off, and the bidirectional switch is switched between the first and second switching elements.
And a control circuit for performing on-control of each of the switching elements with a phase difference. 4. A DC power supply circuit having a first terminal, a second terminal, and a third terminal for providing a midpoint potential between the first and second terminals, a first terminal and a second terminal. A first and a second switching element connected in series with each other between the first and second terminals; a middle point connected between the connection point of the first and the second switching element and the third terminal; A series circuit including a winding having a terminal and a resonance capacitor; a load receiving power supply based on the winding; a bidirectional switch connected between the third terminal and the intermediate terminal; First and second switching elements are alternately turned on and off, and the bidirectional switch is switched between the first and second switching elements.
And a control circuit for performing on-control of each of the switching elements with a phase difference. 5. The resonance type switching power supply device according to claim 1, wherein said bidirectional switch comprises third and fourth switching elements connected in anti-parallel.