JPH03143264A - Forward converter power supply - Google Patents

Abstract

PURPOSE:To simplify a circuit by connecting the series circuit of a capacitor and an auxiliary switch in parallel with a main switch for connecting the pri mary winding of a transformer and by opening and closing the auxiliary switch just before closing the main switch and just after opening it respectively. CONSTITUTION:An electric power of a voltage V1 and a current I1 is fed to the secondary winding of a transformer 5 by switching on or off the DC power of a power supply 1, opening or closing a main switch 2 connected in series with the primary winding of the transformer 5. The series circuit of an auxiliary switch 3 and a capacitor 4 is connected in parallel with the main switch 2. The makes and breaks of the main switch 2 and the auxiliary switch 3 are controlled by a controlling circuit 7 and the auxiliary switch 3 is opened and closed just before closing the main switch 2 and just after opening it respective ly. When opening the main switch 2 the auxiliary switch 3 is closed and the capacitor 4 is changed by the excitation current of the transformer 5 to make the energy of the transformer 5 zero. Then, the charge is discharged from the capacitor 4 to the power supply 1 via the primary winding of the trans former 5. Thereby, no auxiliary winding of the transformer is needed and the circuit is simplified.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a forward converter power supply, and in particular, when power is applied to the transformer with a switch, the
It relates to a forward converter power supply that outputs power energy to the next side.

[Conventional technology]

FIG. 4 is a circuit diagram showing an example of a conventional forward converter power supply. The reset circuit for releasing the energy stored in the transformer has a diode 6 and a capacitor 4 connected in parallel to the switch 2, and an auxiliary switch 3 connected to an auxiliary winding wound around the transformer 5a. The bottom of the tank will be drained. The auxiliary switch 3 is controlled to close after the conduction period of the switch 2 and to open before the switch 2 becomes conductive again. The energy stored in the transformer during the period when the switch 2 is conducting is operated such that after the switch 2 is non-conducting, it is first stored in the capacitor 4 through the diode 12 and then discharged through the auxiliary switch 3 to the input power supply. Ori,
The circuit discharges all of the excitation energy of the transformer 5a to the input power source and optimally resets the transformer 5a.

[Problem to be solved by the invention]

The transformer reset circuit of the conventional forward converter circuit described above requires an auxiliary winding on the transformer in order to discharge the charge once stored in the capacitor to the input power supply side during the non-conducting period of switch 2. There is a problem that the shape of the container becomes larger and the price becomes higher.

[Means to solve the problem]

The forward converter power supply of the present invention includes a switch that intermittently supplies power to the primary winding of a transformer, a capacitor and an auxiliary switch that are connected in parallel to this switch and discharge power stored in the transformer. The control circuit includes a control circuit that causes the auxiliary switch to become non-conductive immediately before the switch becomes conductive, and causes the auxiliary switch to become conductive immediately after the switch becomes non-conductive.

〔Example〕

Next, the present invention will be explained with reference to the drawings. 1 and 3 are circuit diagrams of the first and second embodiments of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of the present embodiment.

The first embodiment includes a switch 2 that intermittently supplies power 1 to the primary winding of a transformer 5, a capacitor 4 connected in parallel to the switch 2, and a capacitor 4 that discharges the power energy stored in the transformer 5. The control circuit 7 includes an auxiliary switch 3 and a control circuit 7 that makes the auxiliary switch 3 non-conductive immediately before the switch 2 becomes conductive, and makes the auxiliary switch 3 conductive immediately after the switch 2 becomes non-conductive.

The second embodiment includes a MOSFET 8 having a parasitic diode as an auxiliary switch of the first embodiment.

Next, the operation will be explained.

When the switch 2 is turned on, power of voltage (2) and current (1) is supplied from the primary side to the secondary side via the transformer 5. At this time, the energy excited in the transformer 5 is applied to the auxiliary switch 3 and the capacitor 4 at a voltage V2. when the switch 2 is non-conducting. Charged (reset) as current I2. Auxiliary switch 3
is controlled by the control circuit 7, becomes non-conductive before the switch 2 becomes conductive, becomes conductive after the switch 2 becomes non-conductive, and excitation current of the transformer 5 when the switch 2 changes from conductive to non-conductive; is expressed by equation (1).

However, VIN is the input voltage, TON is the conduction period of the switch, and L is the inductance of the transformer.

In this way, when the switch 2 becomes non-conductive, the auxiliary switch 3 becomes conductive, and the excitation current of the transformer 5 flows to the capacitor 4, and the energy of the transformer becomes zero during the half cycle of the non-conductive period of the switch 2.

Then, in the next half cycle, the capacitor 4 is discharged through the temporary winding of the transformer 5 to the input power supply 1 side. During the period when switch 2 is non-conducting, the reset voltage of the transformer is v2 VIN
be clamped to.

〔Effect of the invention〕

As explained above, the present invention controls the auxiliary switch connected in parallel to the switch on the primary side of the transformer in conjunction with the disconnection of the switch. Since the accumulated power can be released, it has the effect of simplifying the circuit.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a first embodiment of the present invention, and FIG. 2 is a circuit diagram of a first embodiment of the present invention.
3 is a circuit diagram of the second embodiment of the present invention, FIG. 4 is a circuit diagram of an example of a conventional forward converter power supply, and FIG. 5 is a circuit diagram of an example of a conventional forward converter power supply. FIG. 3 is a waveform diagram for explaining the operation. 1... Input power supply, 2... Switch, 3... Auxiliary switch, 4... Capacitor, 5... Transformer, 6...
・Diode, 7...Control circuit, 8...MOSFE
T.

Claims (1)

[Claims] 1. A switch that intermittently supplies power to the primary winding of a transformer, and a capacitor and auxiliary switch that are connected in parallel to this switch and discharge the power stored in the transformer;
A forward converter power supply comprising: a control circuit that makes the auxiliary switch non-conductive immediately before the switch becomes conductive, and makes the auxiliary switch conductive immediately after the switch becomes non-conductive. 2. MOS having a parasitic diode in the auxiliary switch
The forward converter power supply according to claim 1, characterized in that an FFT is used.