JP2817492B2 - Forward converter snubber circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a snubber circuit for a forward converter.

[0002]

2. Description of the Related Art Conventionally, in a single-rock type forward converter, as shown in FIG. A DC power voltage is extracted through a choke input smoothing circuit including a voltage conversion output diode 9, a coil 10, and a capacitor 11 by a power transformer 3 insulated between secondary windings 2 and 4.

Further, in order to suppress a surge voltage due to a parasitic element when the main switch 13 is turned on and off, a power transformer 3 is used.
Diode 16 and capacitor 1 across both ends of primary winding 2
4, a primary snubber circuit including a resistor 15 is inserted, and a capacitor 1 is connected to both ends 12 of the diodes 8 and 9.
A secondary snubber circuit composed of 8 and 20 and resistors 17 and 19 is inserted.

The control circuit 12 controls the on / off period of the main switch 13 so that the fluctuation of the DC voltage is kept within an allowable range.

[0005]

In the snubber circuit of the conventional forward converter, the electric charges of the capacitors 14, 18, and 20, which have once absorbed the unnecessary energy such as the parasitic elements, are consumed by the resistors 15, 17, 19, and the power loss is obtained. Becomes
There is a problem that the power efficiency of the convanter is reduced, and the power loss is increased as the switching frequency is increased.

[0006]

The circuit of the present invention has a main switch for disconnecting an input DC voltage on the primary side of a transformer for voltage conversion, and a rectifying diode and a choke input on the secondary side of the transformer. In a snubber circuit of a single-type forward converter having a smoothing circuit, a series circuit including a capacitor and a diode is connected to both ends of a secondary winding of the transformer, and a connection midpoint between the two is connected to the choke input smoothing circuit. It has a configuration in which a coil is connected between the output capacitor.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of one embodiment of the present invention.
A series circuit of a capacitor 5 and a diode 6 is connected to both ends of a secondary winding 4 of the power transformer 3, and a coil 7 is connected between a connection midpoint between the two and an output end of a choke input smoothing circuit. A snubber circuit is configured. FIG.
(C) is a signal waveform diagram illustrating a voltage waveform of each part of the present embodiment. FIG. 3A shows the voltage across the main switch 13. First, when the main switch 13 is turned off, the voltage across the main switch 13 is sharply changed to the input voltage due to the energy release of the leakage inductance of the power transformer 3 on the primary side. It rises to E. When the voltage between both ends of the main switch 13 rises to near the input voltage, the diode 6 of the secondary-side snubber circuit conducts, so that the snubber capacitor 5 is reversely charged (FIG. 2B), and the main switch voltage temporarily drops. . At this time, the diode 8 for output rectification switches from the forward voltage to the reverse voltage (FIG. 3C), and becomes in the voltage direction in which the reverse recovery current flows.
, The reverse recovery current is suppressed. Next, after the reverse charging of the capacitor 5 is completed, a free oscillation voltage is generated by the primary inductance and the parasitic capacitance of the power transformer 3,
The power transformer 3 resets itself. On the other hand, on the secondary side of the power transformer 3, the coil 10 is clamped by a capacitor, and the excitation energy is discharged to the capacitor 11 through the diode 9 and the capacitor 5 of the snubber circuit is discharged.
Is also transmitted to the output capacitor 11 via the coil 7 with a stop current, and is effectively used as output power. If the inductance of the coil 7 is set so that the resonance cycle composed of the inductance of the coil 7 of the snubber circuit and the capacitance of the capacitor 5 is sufficiently larger than the switching cycle of the converter, the current flowing through the coil 7 can be made constant. Therefore, the output ripple voltage does not increase.

[0009]

As described above, according to the present invention, a diode is provided on the secondary side of the main transformer of the forward converter.
By connecting a snubber circuit composed of a capacitor and a coil, it is possible to temporarily suppress an increase in the flyback voltage when the main switch is turned off, suppress the recovery current of the diode for output rectification, and improve the efficiency of the converter. Further, the generation of switching noise at the time of turn-off can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIGS. 2A to 2C are signal waveform diagrams showing voltages or currents of respective parts according to the embodiment of the present invention.

FIG. 3 is a circuit diagram of a snubber circuit of a conventional forward converter.

[Explanation of symbols]

 1 Capacitor 2 Primary winding 3 Power transformer 4 Secondary winding 5 Capacitor 6 Diode 7 Coil 8 Diode 9 Diode 10 Coil 11 Capacitor 12 Control circuit 13 Main switch 14 Capacitor 15 Resistor 16 Diode 17 Resistor 18 Capacitor 19 Resistor 20 capacitors

Claims (1)

(57) [Claims] 1. A one-wheel type forward converter having a main switch for disconnecting an input DC voltage on a primary side of a transformer for voltage conversion and a rectifying diode and a choke input smoothing circuit on a secondary side of the transformer. In the snubber circuit, a series circuit composed of a capacitor and a diode was connected to both ends of a secondary winding of the transformer, and a coil was connected between a connection midpoint between the two and an output capacitor of the choke input smoothing circuit. A snubber circuit for a forward converter, having a configuration.