JP2008029158A - Switching power supply apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply apparatus capable of suppressing occurrence of a switching loss or a noise. <P>SOLUTION: A positive bus bar P is connected to one end of a primary winding Np of a transformer TF, a negative bus bar N is connected to the other end via a capacitor C4, and a portion between a collector and an emitter of a main switch Q1 is connected to both ends of the capacitor C4. An output end of a control circuit CTR is connected to a base of the switch Q1 via a delay circuit DL, and a base of an auxiliary switch Q2 is connected to an output end of the control circuit CTR. In the switching power supply configured described above, the auxiliary switch Q2 is turned ON prior to the main switch Q1, so that a zero voltage switch in the main switch Q1 can be realized. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a switching power supply device having a soft switching function.

  In order to reduce switching loss and noise, the switching power supply device has a so-called soft switching function that turns on and off the switching element in a state where the current or voltage is zero.

  As this type of switching power supply device having a soft switching function, there is one in which an auxiliary switching transistor is turned on by a turn-on signal delayed by a delay circuit after the main switching transistor is turned on (see, for example, Patent Document 1).

  In addition, a voltage detection circuit is provided to detect zero-voltage switching by utilizing the charging action of the excitation energy of the windings to the stray capacitance of the transformer, and the drive signal from the drive circuit is inhibited. In some cases, the drive signal of the switching element is formed from the drive signal by the detection signal from the voltage detection circuit, and the switching element is subjected to zero voltage switching by this drive signal (see, for example, Patent Document 2) .)

  Furthermore, even if the load becomes light or no load, the switching loss of the main switching element does not increase, and the efficiency of the rectifying switching element can be improved and the power supply device can cope with a lower output voltage ( For example, see Patent Document 3.)

In addition, in the process until the voltage at both ends of the main switch element reaches zero, the difference between the voltage of the DC power supply and the voltage at both ends of the main switch element is applied to the primary winding. The main switch element tries to turn on with the generated voltage, where the first saturable inductor is selected appropriately, the turn-on is delayed, and the main switch element is turned on when the voltage of the main switch element becomes zero (For example, refer to Patent Document 4).
Japanese Patent Laid-Open No. 06-189538 Japanese Patent Laid-Open No. 08-182318 JP 2002-305876 A JP 2004-069881 A

  FIG. 3 is a circuit diagram showing a soft switching circuit in a conventional switching power supply apparatus. In FIG. 3, the soft switching circuit uses the primary inductance component of the transformer 2 and the resonance of the snubber capacitor 4, and has the lowest voltage. At this point, the main switch 3 is turned on. FIG. 4 shows the voltage V1 and currents I1 and I2 of each part of FIG. In FIG. 3, 1 is a capacitor, 5 is a rectifier diode, 6 is a capacitor, 7 is a rectifier circuit, and 8 is a load.

  Next, the operation of the soft switching circuit of the switching power supply device shown in FIG. 3 will be described. First, during the ON period of the main switch 3, a current I 1 flows through the transformer 2, and energy is accumulated in the transformer 2. Further, since a reverse voltage is generated in the secondary circuit winding of the transformer 2 during this period, the current I2 does not flow through the diode 5.

  Here, when the main switch 3 is turned OFF, the polarity of the voltage induced in the secondary circuit winding of the transformer 2 is reversed, and the energy accumulated in the transformer 2 is released to the secondary circuit. Since is held at a certain value, not all energy is released into the secondary circuit. Therefore, even if the primary side inductance of the transformer 2 and the snubber capacitor 4 resonate due to the residual energy of the transformer 2, the voltage V1 does not completely become “zero” voltage, and there is a problem that switching loss and noise occur.

  This invention is made in view of said situation, and makes it a subject to provide the switching power supply device which can suppress generation | occurrence | production of a switching loss and noise.

  In order to achieve the above object, the present invention provides a transformer having a primary winding and first and second secondary windings, and a rectifier circuit is provided in the second secondary winding of the transformer. One end of the primary winding is connected to one end of the parallel circuit of the main switching element and the capacitor, and a DC voltage is applied between the other end of the parallel circuit and the other end of the primary winding of the transformer. A series circuit of a capacitor and an auxiliary switching element is connected to both ends of the first secondary winding, and a diode is connected in parallel to the auxiliary switching element, and to both ends of the first secondary winding. A series circuit of a diode and a capacitor is connected, and a control circuit is provided at both ends of the capacitor. When the ON signal is given from the control circuit to the main and auxiliary switching elements, the auxiliary switching element is connected to the main switch. It is characterized in that so as to ON earlier than quenching element.

  As described above, according to the present invention, the auxiliary switch is connected to the winding provided separately from the main switch winding in the transformer, and the auxiliary switch is turned on before the main switch so that the zero in the main switch is By realizing the voltage switch, it is possible to suppress the occurrence of switching loss and noise in the main switch.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit configuration diagram showing an embodiment. In FIG. 1, an AC power supply AC is connected to a rectifier circuit RCF, and the AC is rectified by this rectifier circuit RCF and supplied to DC positive and negative buses P and N. . A capacitor C1 is connected between the DC positive and negative buses P and N. TF is a transformer. One end of the primary winding Np of the transformer TF is connected to the DC positive bus P, and the other end is connected to the DC negative bus N via the capacitor C4.

  The collector and emitter of the main switch Q1, which is the main switching element, are connected to both ends of the capacitor C4, and the output terminal of the control circuit CTR is connected to the base of the main switch Q1 via the delay circuit DL. The output terminal of the control circuit CTR is also connected to the base of the auxiliary switch Q2, which is an auxiliary switching element.

The signals given to the bases of these switches Q1 and Q2 are output by feeding back the output voltage V _C5 to the control circuit CTR, amplifying it with an error amplifier amp in the control circuit CTR, and performing PWM modulation with the PWM modulation circuit pwm. This is a signal generated to keep the voltage V _C5 constant.

  The positive end of the capacitor C2 is connected to one end of the secondary winding Ns1 of the transformer TF via a diode D1 of the illustrated polarity, and the negative end of the capacitor C2 is connected to the other end, and the negative bus N is connected to the other end. Is done. Both ends of the capacitor C2 are connected to the control circuit CTR and supplied with a voltage. One end of the secondary winding Ns1 of the transformer TF is connected to the collector of the auxiliary switch Q2 via a series body of a resistor R1 and a capacitor C3, and the emitter of the switch Q2 is the other end of the secondary winding Ns1, that is, a negative polarity. Connected to bus N.

A diode D5, a capacitor C5, and a load L are connected to the output winding Ns2 of the transformer TF. The voltage V _C5 across the capacitor C5 is supplied to the control circuit CTR via the voltage feedback circuit FDB.

  Next, the operation of the embodiment configured as described above will be described with reference to the operation waveform diagram shown in FIG. First, the voltage (forward voltage) induced in the secondary winding Ns1 when the main switch Q1 is turned on is stored in the capacitor C3 with the polarity shown in FIG. 1, and before the next ON signal of the main switch Q1. By turning on the auxiliary switch Q2 provided in the secondary winding Ns1, a voltage corresponding to the input DC voltage is induced in the winding Np of the main switch Q1, and the collector-emitter voltage of the main switch Q1 is set to “0” V To.

When the main switch Q1 is turned on, the capacitor C2 is also charged, and the voltage values V _C20 and V _C30 of the capacitors C2 and C3 constantly become the following voltage values.

V _C20 : Control target voltage (If the voltage of the capacitor C5 is kept at the target value, the voltage of the capacitor C2 becomes a value corresponding to the winding ratio Ns1, Ns2 of the transformer TF.)
V _C30 : Vdc × Ns1 / Np
As described above, when the voltage values V _C20 and V _C30 of the capacitors C2 and C3 are obtained, when the gate ON signal is output from the control circuit CTR, the auxiliary switch Q2 is turned on first. Then, the voltage V _C3 due to the charge stored in the capacitor C3 is applied to the secondary winding Ns1 of the transformer TF, and V _C3 × Np / Ns1 (= Vdc) is applied to the primary winding Np. That is, the collector of the main switch Q1 becomes zero potential, and zero voltage switching ZVS is realized when the main switch Q1 is turned on. Thereafter, the main switch Q1 is turned on with a delay.

During the period in which the main switch Q1 and the auxiliary switch Q2 are simultaneously ON, the capacitor C1 connected to the power source serves as an energy supply source, and excites the primary winding Np of the transformer TF. The capacitor C3 is charged with a voltage value V _C30 = Vdc × Ns1 / Np induced in the secondary winding Ns1 of the transformer TF in a direction in which the current I3 becomes negative. Thereafter, the main switch Q1 and the auxiliary switch Q2 are turned off.

  At this time, since the voltage rise of the main switch Q1 is delayed by the capacitor C4, switching loss and switching loss can be reduced. On the other hand, on the auxiliary switch Q2 side, the capacitor C2 is charged to the control target voltage via the diode D1 by the voltage induced in the secondary winding Ns1. The resistor R1 is inserted for the purpose of limiting the current of the diode D2 and the auxiliary switch Q2.

In the circuit according to the present embodiment, the initial voltages of the capacitors C2 and C3 at the start-up are both “0” V, but the control circuit CTR controls the voltage of the capacitor C2 so as to become the target voltage. The battery is charged to a voltage value V _C20 .

Further, since the capacitor C3 is charged by the voltage value V _C30 = Vdc × Ns1 / Np induced in the secondary winding Ns1 of the transformer TF in the direction in which the current I3 becomes negative during the ON period of the main switch Q1, _Specifically , it is charged to the voltage value V _C30 . Therefore, the period from the start to the time when the capacitor C3 is charged to the voltage value V _C30 is a period in which ZVS cannot be realized even when the main switch Q1 and the auxiliary switch Q2 are turned on at the timing described above.

The circuit block diagram which shows embodiment of this invention. FIG. 6 is a waveform diagram illustrating operation of an embodiment. The conventional circuit block diagram. The wave form diagram explaining operation | movement of the conventional circuit.

Explanation of symbols

TF ... Transformer CTR ... Control circuit DL ... Delay circuit FDB ... Voltage feedback circuit Q1 ... Main switch Q2 ... Auxiliary switches C1 to C5 ... Capacitors D1, D2, D5 ... Diode R1 ... Resistance

Claims (1)

A transformer having a primary winding and first and second secondary windings;
A rectifier circuit is provided in the second secondary winding of the transformer, one end of the parallel circuit of the main switching element and the capacitor is connected to one end of the primary winding, and the other end of the parallel circuit and the primary winding of the transformer Apply a DC voltage across the other end of the wire,
A series circuit of a capacitor and an auxiliary switching element is connected to both ends of the first secondary winding of the transformer, and a diode is connected in parallel to the auxiliary switching element,
A series circuit of a diode and a capacitor is connected to both ends of the first secondary winding, and a control circuit is provided to both ends of the capacitor, and an ON signal is sent from the control circuit to the main and auxiliary switching elements. The switching power supply device is characterized in that the auxiliary switching element is turned on earlier than the main switching element when the power is applied.

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