JP3137155B2 - DC-DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC-DC converter including a push-pull circuit.

[0002]

2. Description of the Related Art FIG. 1 shows a conventional push-pull circuit including a push-pull circuit.
3 shows a C-DC converter. In this DC-DC converter, a half-bridge circuit is connected between one end 1a and the other end 1b of the DC power supply 1, and a full-wave rectifier circuit and a choke input type smoothing circuit are provided at the output stage. I have.

[0003] The half-bridge type inverter circuit comprises first and second switching elements Q1, Q2 comprising field effect transistors having diodes Da, Db connected between one end 1a and the other end 1b of the DC power supply 1. And a series circuit of the first and second capacitors C1 and C2. One end of a primary winding N1 of the output transformer T is connected to the interconnection point of the first and second switching elements Q1 and Q2, and the other end of the primary winding N1 is connected to the first and second capacitors C1 and C1. It is connected to the connection midpoint of C2. The secondary winding N2 of the transformer T is divided by a center tap 2 into first and second windings N2a and N2b. First and second diodes D1 and D2 for forming a full-wave rectifier circuit are connected to one end and the other end of the secondary winding N2, respectively. The smoothing circuit includes a choke coil L0 and a capacitor C0, and is configured as a choke input type. That is, the input terminal of the choke coil L0 is connected to the cathodes of the first and second diodes D1 and D2, and the smoothing capacitor C0 is connected to the output terminal of the choke coil L0 and the center tap 2.
Is connected between. The output terminals 3 and 4 are connected to both terminals of the smoothing capacitor C0. The control circuit 5 is connected between the output terminals 3 and 4 and the control terminals (gates) of the pair of switching elements Q1 and Q2, and controls the first and second PWM pulses P1 and P2 for keeping the output voltage constant.
Occurs. The first and second PWM pulses P1 and P2 are generated alternately with a pause between them.

[0004]

[Operation] The DC-DC converter of FIG. 1 operates as follows. First, when the power is turned on, the first and second capacitors C1 and C2 are charged to 1/2 of the voltage E of the power supply 1, respectively. Thereafter, the first and second switching elements Q1
, Q2 are turned on alternately with a pause between each other. While the first switching element Q1 is on, a current based on the discharge of the first capacitor C1 flows in a closed circuit including the first switching element Q1, the primary winding N1, and the first capacitor C1. Further, the power supply 1, the first switching element Q1, the primary winding N1, and the second capacitor C
Current also flows through the closed circuit consisting of When the first and second switching elements Q1 and Q2 are both turned off and then the second switching element Q2 is turned on, the second
A current flows through a closed circuit including the switching element Q2, the second capacitor C2, and the primary winding N1, and the power supply 1, the first capacitor C1, the primary winding N1, and the second switching element Q2. Current also flows through the closed circuit.
As a result, a reverse current flows alternately through the primary winding N1, and an AC voltage is obtained through the secondary winding N2. Secondary winding N2
When an upward voltage is induced in the circuit, a current flows through a circuit including the first winding N2a, the first diode D1, the choke coil L0, and the capacitor C0. When a downward voltage is induced in the secondary winding N2, the second winding N2b, the second diode D2, the choke coil L0, and the capacitor C0
Current flows through the circuit consisting of

[0005]

When the first switching element Q1 is turned off, a surge voltage is generated across the primary winding N1, but when the second switching element Q2 is turned on, this surge voltage disappears. The voltage of the primary winding N1 becomes zero. Therefore, the second switching element Q2
Is applied with the voltage (E / 2) of the second capacitor C2. Since the second switching element Q2 is turned on while a voltage is applied, zero volt switching is not achieved, and switching loss occurs. For this reason,
Problems such as a decrease in efficiency and generation of noise occur. A similar problem occurs when the first switching element Q1 is turned on.

Accordingly, an object of the present invention is to provide a DC-DC device capable of turning on a switching element with this voltage being zero or low, that is, capable of performing soft switching.
To provide a converter.

[0007]

In order to achieve the above object, the present invention provides a series circuit of a DC power supply and first and second switching elements connected between one end and the other end of the DC power supply. And an inverter circuit including a primary winding of a transformer to which a voltage is alternately applied via the first and second switching elements, a secondary winding of the transformer, and the secondary winding. A full-wave rectifier circuit, a choke input type smoothing circuit connected to the rectifier circuit, an inductance connected in series to the primary winding or a leakage inductance of the primary winding, the first and second switch control to alternately on-off controls the switching elements
And the control circuit includes a first switch and a second switch.
Pulse for controlling the on / off of the switching element
Occurs without any dead time and the smoothing
In order to control the output of the road constant,
The inductor configured to change a repetition frequency;
Release of the stored energy of the first and second switches.
Occurs based on switching of the switching element on and off, and
During the period of discharging the stored energy, the voltage applied to the primary winding is reduced.
The inductance so that the applied voltage is substantially zero.
Are connected to the inverter circuit, and the inverter circuit
Does not include a capacitor for current resonance.
Related to a DC-DC converter. As described in claim 2, an LC series resonance circuit can be connected in parallel with the transformer. Further, an LC parallel resonance circuit can be connected in series with the primary winding. Further, as described in claim 4, the output voltage can be adjusted by controlling the inductance as a variable inductance.

[0008]

In the invention of each claim, the inductance (including the leakage inductance) or the variable inductance is, for example, a voltage drop element when the first switching element is turned off and the second switching element is turned on. Function. That is, energy is accumulated in the inductance or the variable inductance during the ON period of the first switching element, and this energy is released through the second switching element after the first switching element is turned off. Therefore, the second switch
Soft switching of the switching element becomes possible. That is,
The energy of the parasitic capacitance of the switching element 2 is regenerated.
Zero volt switching of the second switching element
Becomes possible. Matata - the voltage descent of the inductance or variable inductance at-off is substantially equal to the voltage of the power source side, the voltage of the primary winding becomes almost zero, the voltage of the secondary winding becomes substantially zero. When the release of the energy of the inductance or the variable inductance ends, a current starts flowing in the primary winding and the second switching element in a direction opposite to the current direction. But the smoothing circuit is choke
Because it is an input type, it is stored in the choke coil
The conduction of the rectifier circuit is maintained by the release of energy,
The secondary winding is short-circuited and then the voltage of the secondary winding
Is obtained. Therefore, the invention of each claim
According to the soft switch
Not only possible but also dead time
Despite the control that does not have
The short circuit of the secondary winding occurs due to the function of the
Output state similar to the case with
Change in the ratio between the time when
Thus, the output voltage can be controlled. Ma
In addition, the dead time of the first and second switching elements is reduced.
Since it is turned on and off alternately without having
The configuration is simplified. According to the first to third aspects of the present invention, the period during which the voltage of the transformer becomes zero due to the release of the stored energy of the inductance becomes substantially constant.
It is possible to adjust the output voltage by changing the ON-OFF repetition frequency of the switching elements (cycle)
Wear. According to the fourth aspect of the present invention, since the period during which the voltage of the transformer becomes zero changes by changing the value of the variable inductance, the on / off frequency of the first and second switching elements is kept constant to reduce the output voltage. Can be adjusted. According to the second and third aspects of the present invention, the output voltage of the transformer can be reduced by the resonance operation of the resonance circuit. Can be prevented. That is, the range of the on / off frequency can be limited.

[0009]

First Embodiment Next, referring to FIGS. 2 and 3, a choke input type DC-D according to a first embodiment of the present invention will be described.
The C converter will be described. However, in FIG. 2 and FIGS. 4, 5, 6, 9, and 10, which will be described later, the same parts as those in FIG.

In FIG. 2, a DC power supply 1 and a diode D
a, Db built-in insulated gate type (MOS type) field effect transistors Q1, Q2, first and second capacitors C
The main circuit comprising 1, C2, transformer T, rectifier diodes D1, D2, choke coil L0, and smoothing capacitor C0 has the same configuration as the main circuit of FIG. The circuit shown in FIG. 2 has an inductance (reactor) L1 composed of a core and a coil connected in series to a primary winding N1 of a transformer T.
And the first and second switching elements Q1, Q2
2 is different from the circuit of FIG.

The control circuit 6 comprises voltage detecting voltage dividing resistors R 1 and R 2 connected between the output terminals 3 and 4, a variable frequency (period) pulse generating circuit 7, and a NOT circuit 7. The pulse generating circuit 7 connected to the voltage dividing point of the voltage detection resistors R1 and R2 includes a voltage controlled oscillator (VCO) and has a square wave shown in FIG. 3A having a frequency corresponding to the detected voltage (control voltage). It is configured to generate a pulse train. The output terminal of the pulse generation circuit 7 is connected to the control terminal (gate) of the first switching element Q1. Also,
This output terminal is connected via a NOT circuit 8 to the control terminal (gate) of the second switching element Q2. The pulse train of FIG. 3B obtained by inverting the phase of the pulse train of FIG. 3A is applied to the second switching element Q2. The VCO of the pulse generation circuit 7 and the voltage detection resistors R1, R
2, an error amplifier may be connected to generate a voltage corresponding to the difference between the detection voltage and the reference voltage, and apply the voltage to the VCO.

[0012]

[Operation] First and second switching elements Q1,
As shown in FIGS. 3A and 3B, Q2 is alternately turned on and off without a pause. While the first switching element Q1 is on, a current flows in the first direction from the top to the bottom of the primary winding N1 as in the circuit of FIG. As a result, also on the secondary side, a current flows through the first diode D1 to the choke coil L0 and the capacitor C0 as in the circuit of FIG. Further, magnetic energy is stored in the inductance L1 in series with the primary winding N1. FIG.
When the first switching element Q1 is turned off at time t1, the current for releasing the stored energy of the inductance L1 is changed to the inductance L1, the second capacitor C2, the second switching element Q2, and the primary winding N1. Flows in a closed circuit consisting of This current flows as a reverse current in the second switching element Q2. When a current flows through the inductance L1, a voltage having a polarity opposite to the charging voltage of the second capacitor C2 is obtained in the inductance L1, and the voltage of the second capacitor C2 is canceled by the voltage of the inductance L1. , A second capacitor C connected to the second switching element Q2.
Voltage 2 is not applied as it is. Therefore, the second switching element Q2 changes from the off state to the on state in a state where the voltage between both ends (drain-source voltage) is low. As a result, soft switching is performed, and switching loss and noise are reduced. When the release of the energy of the inductance L1 is completed, a second capacitor C2, an inductance L1, a primary winding N1, and a second switching element Q2 are used to move the primary winding N1 from bottom to top. Direction current flows. First switching element Q
The same operation as above occurs when 1 goes from off to on.

In the period during which the energy of the inductance L1 is released, the voltage of the second capacitor C2 is canceled by the voltage drop of the inductance L1, so that no voltage is applied to the primary winding N1. No voltage is obtained at N2. Therefore, the first and second diodes D1 and D2 are released by releasing the stored energy of the choke coil L0.
, D2 are turned on, and currents I _D1 and I _D2 flow during the period from t1 to t2, respectively, as shown in FIG. As a result, the secondary winding N2 is short-circuited by the diodes D1 and D2 during the period from t1 to t2. Diode D1,
During the period from t to t2 when both of D2 are on, that is, at T2, the rectified output voltage V0 on the secondary side of the transformer T is zero as shown in FIG. The period T2 during which the output voltage of the transformer T becomes zero is determined by the inductance L1 and the magnitude of the current flowing therethrough. If the current is constant, T2 will be substantially constant.

When controlling the DC output voltage, the on / off period T1 of the first and second switching elements Q1, Q2 is controlled.
change. 3 shows a control state when the DC output voltage between the output terminals 3 and 4 is high before time t3, and shows a control state when the DC output voltage is low after time t3. That is,
Assuming that the DC output voltage is lower than before t3, t
3 As shown later, the generation cycle T1 of the output pulse of the variable frequency pulse generation circuit 7 becomes longer, and the duty ratio (2 T3
/ T1) is increased, and the operation is to increase the DC output voltage.

[0015]

FIG. 4 shows a DC-DC converter according to a second embodiment. The circuit of FIG. 4 is obtained by adding a series resonance circuit of an inductance La and a capacitor Ca to the circuit of FIG. This LaCa series resonance circuit is connected in parallel to the secondary winding N2. The LaCa series resonance circuit is set to resonate in a region where the on / off frequency of the first and second switching elements Q1 and Q2 is high and short-circuit the secondary winding N2. For example, when the load in the circuit of FIG. 4 becomes light and the voltage between the output terminals 3 and 4 rises, t3 in FIG.
As previously shown, the first and second switching elements Q1
, Q2 have a shorter on / off period T1, and the repetition frequency increases. When this repetition frequency is at or near the resonance frequency of the LaCa resonance circuit, the impedance is reduced, the secondary winding N2 is substantially short-circuited, and the rectified output voltage V0 is reduced. Therefore, in order to obtain a predetermined DC output voltage, the period T1 can be lengthened, that is, the frequency can be reduced, and operation at a high frequency can be prevented. Since the operation generally becomes unstable in a high frequency region, limiting the operation in the high frequency region with the resonance circuit of FIG. 4 has significance in stabilizing the operation. The circuit of FIG. 4 naturally has the same operation and effect as the circuit of FIG.

[0016]

Third Embodiment FIG. 5 shows a DC-DC converter according to a third embodiment. The circuit of FIG. 5 is obtained by adding a parallel resonance circuit of an inductance Lb and a capacitor Cb to the circuit of FIG. The Lb and Cb parallel resonance circuits are connected in series to the primary winding N1 and are set to resonate when the on / off frequency of the first and second switching elements Q1 and Q2 becomes high under light load or the like. ing. The on / off frequency of the first and second switching elements Q1, Q2 is Lb
, Cb, or near the resonance frequency of the parallel resonance circuit, the impedance of the Lb, Cb parallel resonance circuit increases, the primary winding N1 is disconnected from the power supply side, and the rectified output voltage V0 decreases. As a result, the on / off frequency can be reduced to obtain a predetermined DC output voltage, and the same operation and effect as the circuit of FIG. 4 can be obtained.

[0017]

Fourth Embodiment FIG. 6 shows a DC-DC converter according to a fourth embodiment. The circuit of FIG. 6 is obtained by replacing the inductance L1 of FIG. 2 with a variable inductance Lx. The variable inductance Lx includes a saturable magnetic core 11, a main winding 12, and a control winding 13. The inductance L of the main winding 12 changes according to the magnetic field strength H of the core 11 as shown in FIG. That is, until the magnetic flux density B of the core 11 reaches the saturation region, the magnetic permeability μ and the inductance L gradually increase as the magnetic field intensity H increases, and in the saturation region, μ and L decrease as H increases. . Since the strength H of the magnetic field can be controlled by the current Ic of the control winding 13, the inductance value can be controlled by using a region having a positive slope or a region having a negative slope of the curve L shown in FIG. In this embodiment, the control current Ic is set so as to obtain the magnetic field strength H1.

The period T2 in which the rectified output voltage V0 in FIG. 3 becomes zero can be changed by changing the inductance value of the variable inductance Lx. In the embodiment of FIG. 6, the amplifier 1 is connected between the output terminals 3 and 4 and the control winding 13.
4 for supplying a control current Ic corresponding to the DC output voltage to the control coil 13. In this method, the period T2 during which the output voltage V0 shown in FIG. 8C is zero is changed, and the control terminal of the first and second switching elements Q1 and Q2 is supplied from the control circuit 15 with a constant on / off period T1. 8 (A) and 8 (B) are supplied. Thus, the duty ratio of the rectified output voltage V0 can be changed, and the DC output voltage can be adjusted. The embodiment shown in FIG. 6 has the same effect as the embodiment shown in FIG.

[0019]

Fifth Embodiment FIG. 9 shows a DC-DC converter according to a fifth embodiment. The circuit of this embodiment has a circuit in which two saturable reactors, ie, mag amplifiers M1 and M2, are connected in parallel via diodes 16 and 17 instead of one variable inductance Lx in FIG. The first and second mag-amps M1 and M2 include cores 18 and 19, main windings 20 and 21, and control windings 22 and 23. The main windings 20 and 21 are connected via diodes 16 and 17 between the connection point between the first and second switching elements Q1 and Q2 and one end of the primary winding N1, respectively. The directions of the two diodes 16, 17 are opposite to each other. The two control windings 22, 23 are connected in series with each other and are driven by the output of the amplifier 14.

When the first switching element Q1 is on and during the period of discharging the stored energy of the first mag amplifier M1, the diode 16 is on, and a current flows from the top to the bottom of the primary winding N1. During the ON period of the second switching element Q2 after the end of the release of the energy of the first mag-amp M1, a current based on the discharge of the second capacitor C2 flows from the bottom of the primary winding N1 upward. Later, the current flows through the main winding 21 and the diode 17 of the second mag-amp M2. A current flows through the diode 17 even during the period of discharging the stored energy of the second mag amplifier M2. Since the mag-amps M1 and M2 function as variable inductances, the circuit of FIG. 9 can obtain the same effect as that of FIG. 6 by the same control as that of FIG.

[0021]

Sixth Embodiment A sixth embodiment shown in FIG.
This is a circuit in which a diode 24 is added to the circuit shown in FIG. The diode 24 is connected between the first and second switching elements Q1 and Q2 in a direction reversely biased by the voltage of the power supply 1. The first mag-amp M1 is connected to the cathode of the diode 24 via the diode 16, and the second mag-amp M2 is connected to the anode of the diode 24 via the diode 17. The diode 24 prevents the first and second switching elements Q1, Q2 from being directly connected in series. Therefore, even if the first and second switching elements Q1 and Q2 have low impedance at the same time, the first and second mag-amps M1 and M2 are interposed therebetween to prevent an excessive current from flowing. You. In the circuit of FIG.
Others are substantially the same as those in FIGS. 6 and 9, and thus have the same effects.

[0022]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) The rectifier circuit on the secondary side of the transformer T can be changed to a bridge-type rectifier circuit other than the center tap type full-wave rectifier circuit. (2) Instead of providing an independent inductance L1,
The transformer is configured so that the leakage magnetic flux between the primary winding N1 and the secondary windings N2a and N2b becomes large, and the leakage inductance (leakage inductance) of the primary winding N1 is L1.
Can be used as (3) The LaCa series resonance circuit of FIG. 4 can be connected in parallel to the primary winding N1, or a tertiary winding can be provided in the transformer T and connected in parallel here. Further, by providing a gap in the transformer core, a leakage inductance such as a secondary winding is generated, and this leakage inductance can be used instead of the independent inductance La. (4) In the first to sixth embodiments, third and fourth switching elements Q3 and Q4 are connected instead of the first and second capacitors C1 and C2, and the first to fourth switching elements Q1 Q4 to form a full bridge circuit, and the first and fourth switching elements and the second and third switching elements can be alternately turned on and off. (5) In the circuits of FIGS. 6, 9 and 10, the amplifier is an error amplifier, and an output corresponding to the difference between the detected value of the output voltage and the reference voltage is supplied to the control winding 13 or 22 or 23. Can be configured. (6) The variable inductance Lx shown in FIG. 6 can be formed in a quadrature transformer configuration (the main winding 12 and the control winding 13 are wound around a ferrite core by orthogonal coupling).

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a conventional DC-DC converter.

FIG. 2 is a circuit diagram showing a DC-DC converter according to the first embodiment.

FIG. 3 is a waveform chart showing a state of each unit in FIG. 2;

FIG. 4 is a circuit diagram showing a DC-DC converter according to a second embodiment.

FIG. 5 is a circuit diagram showing a DC-DC converter according to a third embodiment.

FIG. 6 is a circuit diagram showing a DC-DC converter according to a fourth embodiment.

FIG. 7 is a characteristic diagram of the variable inductance of FIG. 6;

FIG. 8 is a waveform chart showing a state of each unit in FIG. 6;

FIG. 9 is a circuit diagram illustrating a DC-DC converter according to a fifth embodiment.

FIG. 10 is a circuit diagram showing a DC-DC converter according to a sixth embodiment.

[Explanation of symbols]

 L1 inductance Q1, Q2 switching element T transformer

Claims (4)

(57) [Claims] A DC power supply; a series circuit of first and second switching elements connected between one end and the other end of the DC power supply;
An inverter circuit including a primary winding of a transformer to which a voltage is alternately applied via the switching element; a secondary winding of the transformer; a full-wave rectifier circuit connected to the secondary winding; A choke input type smoothing circuit connected to the rectifier circuit; an inductance connected in series to the primary winding or a leakage inductance of the primary winding; and the first and second switching elements are alternately turned on. A switch control circuit for off-control;
A circuit turns on and off the first and second switching elements.
There is virtually no dead time for the pulse to control
And the output of the smoothing circuit is controlled to be constant.
In order to change the repetition frequency of the on / off control,
And the release of the stored energy of the inductance is controlled by the first
And on / off switching of the second switching element.
During the discharge of the stored energy.
So that the voltage applied to the next winding is substantially zero.
An inductance is connected to the inverter circuit, and the inverter circuit includes a current resonance capacitor.
A DC-DC converter characterized in that there is no DC-DC converter. 2. A series resonance circuit of a capacitor and an inductance is connected in parallel to a primary winding or a secondary winding of the transformer or in parallel via a tertiary winding, and a resonance frequency of the series resonance circuit is reduced. 2. The DC-DC converter according to claim 1, wherein the first and second switching elements are set to resonate in a high on / off repetition frequency region.
DC converter. 3. A parallel resonance circuit of a capacitor and an inductance is connected in series with a primary winding of the transformer,
2. The DC-DC converter according to claim 1, wherein a resonance frequency of the parallel resonance circuit is set so as to resonate in a region where on / off repetition frequencies of the first and second switching elements are high. 4. A direct-current power supply; a series circuit of first and second switching elements connected between one end and the other end of the direct-current power supply;
An inverter circuit including a primary winding of a transformer to which a voltage is alternately applied via the switching element; a full-wave rectifier circuit connected to the secondary winding; a secondary winding of the transformer; A choke input type smoothing circuit connected to the rectifier circuit; a variable inductance connected in series to the primary winding; and a first and a second switching element of the inverter circuit having substantially a dead time. Do not turn on
A switch control circuit for performing off control; and an inductance control circuit for controlling an inductance value of the variable inductance so as to control the output voltage of the smoothing circuit to be constant , wherein the control circuit includes the first and second control circuits.
And on / off control of the second switching element.
Constant repetition of pulses with virtually no dead time
The discharge of the stored energy of the inductance is caused by the first cycle .
And on / off switching of the second switching element.
During the discharge of the stored energy.
So that the voltage applied to the next winding is substantially zero.
An inductance is connected to the inverter circuit, and the inverter circuit includes a current resonance capacitor.
A DC-DC converter characterized in that there is no DC-DC converter.