JP3483501B2 - Drive circuit for synchronous rectifier circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION
The present invention relates to a rectifier circuit that forms a secondary output circuit, and particularly to a synchronous rectifier type rectifier circuit.

[0002]

2. Description of the Related Art FIG. 3 shows the circuit configuration of a forward converter having a synchronous rectification rectifier circuit according to the prior art. In FIG. 3, a main switching element 103 is connected in series to a primary coil of a main transformer 104, and a parallel circuit 102 and a DC power supply 101 form a primary circuit. On the secondary side of the main transformer 104, a rectifying switch element 105 and a freewheeling switch element 106 constitute a synchronous rectifying circuit, and a reactor 107 is provided at the output end.
A smoothing circuit including a capacitor 108 and a capacitor 108 is provided.

[0003]

The gate signal Q output from the control circuit 110 is input to the gate terminal of the main switch element 103 to control the main switch element 103 to be turned on / off. In addition, the gate signal Q ″ output from the control circuit
Supplies an on / off signal to the primary coil of the drive transformer 109 in antiphase with the gate signal Q. Since both ends of the secondary coil of the drive transformer 109 are connected to the gate terminal and the source terminal of the freewheeling switch element 106, the freewheeling switch element 106 is on / off controlled by the gate signal Q ″. Since the drive transformer 109 is operated by the gate signal Q ″ having an opposite phase to the signal Q, when the pulse width of the gate signal Q becomes narrower, the pulse width of the gate signal Q ″ becomes wider contradictory. The drive transformer is in the ON state while the
A countermeasure against saturation of the transformer 109 is required. Further, according to the pulse width of the gate signal Q ″, the control circuit 11
The drive power from 0 also increases.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned drawbacks of the prior art. The freewheeling switch element is turned on by the flyback voltage of the main transformer, and the freewheeling switch element is turned on. In order to turn off, the energy stored in the gate terminal of the freewheeling switch element is discharged by the drive circuit including the first switch element, the pulse transformer, and the second switch element, and turned off. At this time, the pulse transformer is driven by the gate signal Q ', but after the gate signal Q'is output, the gate signal Q for controlling the main switch element is output.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a circuit configuration of a drive circuit of a synchronous rectification circuit according to the present invention, and FIG. 2 is a gate signal Q, a gate signal Q ', and a main switch element V.
FIG. 7 is a signal waveform diagram of _DS , a rectifying switch element, and a freewheeling switch element V _GS .

In FIG. 1, the primary side of the main transformer 7 is
It is composed of a main switch element 1, a parallel capacitor 12 and a DC power supply 11 which are connected in series to the primary coil. The secondary side of the main transformer 7 is provided with a synchronous rectifying circuit composed of a rectifying switch element 2 and a freewheeling switch element 3. Further, a reactor 13 and a capacitor 14 are provided at the output end.
Is provided.

The main switch element 1 provided in the primary coil of the main transformer 7 is controlled by a control circuit 10 which sends out a gate signal Q. The control circuit 10 and the main switch element 1
A delay circuit 9 is provided between and. In addition, the delay circuit 9
The signal line taken out between the control circuit 10 and the control circuit 10 is connected to the gate terminal of the first switch element 4, and the control voltage V is applied to the other end of the pulse transformer 8 whose one end is connected to the first switch element 4. _CC is connected.

At both ends of the secondary coil of the pulse transformer 8, a series circuit composed of a resistor 17 and a diode 18 and
A series circuit composed of two resistors 15 and 16 is connected in parallel. Further, a gate terminal is connected to an intermediate connection point between the two resistors 15 and 16, and a drain terminal is connected to a gate terminal of the freewheeling switch element 3, A second switch element 5 having a source terminal connected to a connection point between the drain terminal of the freewheeling switch element 3 and one end of the resistor 16 is provided. Also,
A diode 6 in which the cathode terminal is connected to the gate terminal of the reflux switch element 3 and the anode terminal is connected between one end of the secondary coil of the main transformer 7 and the rectifying switch element 2.
Are provided to form the drive circuit of the synchronous rectification circuit.

Next, the operation of the drive circuit of the synchronous rectification circuit according to the present invention will be described with reference to the waveform diagram shown in FIG.
The gate signal Q shown in FIG. 2 (a) is a drive signal for controlling on / off of the main switch element 1, and the gate signal Q'shown in FIG. 2 (b) is for controlling on / off of the first switch element 4. It is a drive signal. As is apparent from FIGS. 2A and 2B, the two gate signals Q and Q ′ have the same phase, but the gate signal Q ′ has a wider pulse width and is turned on earlier than the gate signal Q. Will be turned off later.

The drain-source voltage V _DS of the main switch element 1 is as shown in FIG. 2C, and the gate-source voltage V _GS of the rectifying switch element 2 and the freewheeling switch element 3 is shown in FIG. This is as shown in FIG. 2D and FIG. V _GS of the rectifying switch element 2 is turned on / off in synchronization with the gate signal Q. On the other hand, V _GS of the freewheeling switch element 3 is turned on by the flyback voltage of the main transformer 7 accompanying the turning off of the gate signal Q, and turned off by turning on the second switching element along with the rising of the gate signal Q ′, and for rectification. It can be seen that the switch element 2 is turned off before it is turned on.

[0011]

As described above, in the drive circuit of the synchronous rectification circuit according to the present invention, the flyback voltage of the main transformer is used to turn on the freewheel switch element, and the freewheel switch element is passed through the pulse transformer. Is turned off, the drive power for control can be reduced and the snubber circuit on the primary side can be downsized. Further, since the first switching element provided in the primary coil of the pulse transformer is on / off controlled by the gate signal having the same phase as the main switching element, the maximum pulse width can be specified,
Countermeasures for saturation of pulse transformers are easy.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of a drive circuit of a synchronous rectification circuit according to the present invention.

FIG. 2 is a waveform diagram.

FIG. 3 is a block diagram showing a circuit configuration of a drive circuit of a synchronous rectification circuit according to a conventional technique.

[Explanation of symbols]

1-5 switch elements 6,18 diode 7,8 transformer 9 Delay circuit 10 Control circuit 11 DC power supply 12, 14 capacitors 13 reactors 15-17 resistance

Claims (2)

(57) [Claims] 1. A forward converter in which a secondary output circuit is provided with a synchronous rectifying circuit comprising a rectifying switch element and a freewheeling switch element, between a main switch element connected to a primary coil of a main transformer and a control circuit. A delay circuit provided in the first switch element, a first switch element that is turned on / off by inputting a gate signal through a signal line provided between the delay circuit and the control circuit, and a first switch element. A pulse transformer having one end connected to a coil and the other end connected to a control voltage V _CC , and a gate terminal and a source terminal connected via a secondary coil of the pulse transformer, and a drain terminal connected to the gate terminal of the freewheeling switch element. The cathode terminal is connected to the gate terminal of the second switching element and the return switching element that are connected, and the anode terminal is connected to one end of the secondary coil of the main transformer. The drive circuit of the synchronous rectification circuit is configured by the diode connected between the rectifying switch element and the flyback voltage of the main transformer generated when the main switch element is turned off is input to the gate terminal via the diode. The energy stored in the gate terminal of the freewheeling switch element that is turned on is discharged with the second switch element that constitutes the drive circuit is turned on, and the freewheeling switch element is turned off. The drive circuit of the synchronous rectification circuit characterized by. 2. A gate signal output from the control circuit,
A gate signal Q for controlling ON / OFF of the main switching element via a delay circuit and a gate signal Q'having the same phase as the gate signal Q but different pulse widths are used. Before the off-controlled rectifying switch element is turned on, the free wheeling switch element is turned off via the first switch element that is turned on by inputting the gate signal Q '. The drive circuit of the synchronous rectifier according to claim 1.