JP2000125549A - Switching power unit realizing on/off control without auxiliary power - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the start/stop of the oscillation of a switch element without auxiliary power. SOLUTION: A switch 4 is connected to a secondary winding wire 32 of a transformer 3, formed of a primary winding wire 31 and the secondary winding wire 32 which is electrically insulated from the primary winding wire 31. An AC current is made to flow to the primary winding wire 31 by using the feet that the inductance, of the primary winding wire 31 is different, when the switch 4 is open and when it is shorted. The difference of voltages at both ends is read, and the start/stop of the oscillation of the switch element 10 is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply, and more particularly to a circuit for stopping oscillation of a switching power supply by an external signal.

[0002]

2. Description of the Related Art Conventionally, as a circuit for stopping oscillation of a switching power supply by an external signal, as shown in FIG.
A method has been employed in which a signal insulated via a photocoupler is sent to an oscillation stop circuit.

[0003]

[0005] Photocoupler LED
The start or stop of the oscillation is determined by passing a current through the LED. In either case, an auxiliary power supply for supplying a current to the LED is required. For example, in the case where oscillation is started by flowing a current to the LED, the auxiliary power supply must be in a state where the current can be supplied to the LED at any time even while the oscillation is stopped. An auxiliary power supply is also required when stopping the oscillation by passing a current through the LED.

SUMMARY OF THE INVENTION An object of the present invention is to provide a circuit capable of stopping oscillation from an isolated outside without an auxiliary power supply.

[0005]

SUMMARY OF THE INVENTION In a transformer having a primary winding and a secondary winding that are insulated from each other, the inductance of the primary winding differs between when the secondary winding is open and when the secondary winding is short-circuited. Therefore, the voltage across the primary winding when an alternating current is applied to the primary winding differs between when the secondary winding is open and when it is short-circuited.

Since the DC voltage obtained by rectifying and smoothing the voltage at both ends of the primary winding is different between when the secondary winding is open and when it is short-circuited, the oscillation can be stopped by using this.

[0007]

When the secondary winding of the transformer is short-circuited, the inductance at both ends of the primary winding becomes a leakage inductance deviating from the coupling between the primary winding and the secondary winding, and the AC voltage at both ends of the primary winding is obtained. Decreases in proportion to the decrease in inductance.

Since the DC voltage obtained by rectifying and smoothing the AC voltage across the primary winding is also proportional to the inductance of the primary winding, this voltage can be used as a signal for starting and stopping the oscillation of the switching element.

According to the first aspect of the present invention, the AC current applied to the primary winding is generated by an AC generation circuit.

According to the second aspect of the present invention, the AC current applied to the primary winding is obtained from an AC power supply via an impedance element. As an impedance element, a resistor, an inductor, a capacitor, and a combination thereof can be used as long as the element has an impedance to alternating current.

[0011]

1 is a circuit diagram showing a switching power supply according to an embodiment of the present invention.

In the circuit shown in FIG. 1, when the switch 4 is open, the voltage across the primary winding 31 of the transformer 3 is high, so that the capacitor 6 is charged with a high voltage. When the switch 4 is short-circuited, a low voltage is charged. The oscillation stop circuit 1 reads the voltage difference between the capacitors 6 and starts or stops the oscillation of the oscillation control circuit 11.

FIG. 2 is a circuit diagram showing a switching power supply according to an embodiment of the present invention.

In FIG. 2, the primary winding 31 of the transformer 3
Is supplied with an AC current from an AC power supply via a capacitor 16 and a resistor 17. More specifically, the current supplied from the AC power supply flows through the capacitor 16 in one direction, so that the capacitor 16 is charged. Then, the electric charge of the capacitor 16 flows through the resistor 17 and the primary winding 31 and is discharged. The operation by opening and shorting of the switch 4 is the same as in FIG.

Each of the circuits shown in FIGS. 1 and 2 is an example of a circuit to which a single converter for outputting a DC voltage is applied. However, the principle of the present invention is applied to a circuit to which a multi-stone converter is applied and also to an AC voltage. Can also be used for an inverter circuit that outputs

[0016]

As compared with the conventional method shown in FIG. 3, the cost can be reduced because no auxiliary power supply is required, and the economic effect is large.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a switching power supply according to the first embodiment.

FIG. 2 is a circuit diagram showing a switching power supply according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing an example of a conventional system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oscillation stop circuit 2 AC generation circuit 3 Transformer 4 Switch circuit 5 Diode 6 Capacitor 7 DC power supply 8 AC power supply 9 Load circuit 10 Switch element 11 Oscillation control circuit 12 Transformer 13 Diode 14 Capacitor 15 Bridge rectifier 16 Capacitor 17 Resistance 18 Photocoupler 19 Auxiliary power supply 31 Primary winding of transformer 32 Secondary winding of transformer

Claims (2)

[Claims] A switching power supply device inserted between the DC power supply and the load circuit for supplying electric energy of the DC power supply to a load circuit electrically isolated from the DC power supply; An oscillation stop circuit capable of stopping the oscillation of the switching element of the switching power supply device by an external signal, an AC generation circuit for receiving an electric power supplied from the DC power supply to generate an AC signal; A transformer that outputs an AC signal insulated from the secondary winding and a rectifying and smoothing circuit that rectifies and smoothes the voltage across the primary winding of the transformer; A switch circuit is connected to the line, and an external signal input terminal of the oscillation stop circuit is connected to an output of the rectifying / smoothing circuit, thereby enabling on / off control without an auxiliary power supply. Switching power supply. 2. A switching power supply device inserted between the AC power supply and the load circuit to supply electric energy of the AC power supply to a load circuit electrically insulated from the AC power supply. An oscillation stop circuit that can stop the oscillation of the switching element of the switching power supply device by an external signal; and a voltage of the AC power supply is input to the primary winding via an impedance element and is isolated from the secondary winding. A transformer for outputting an AC signal, and a rectifying and smoothing circuit for rectifying and smoothing the voltage across the primary winding of the transformer are added. A switch circuit is connected to the secondary winding of the transformer. A switching power supply device having a signal input terminal connected to an output terminal of the rectifying and smoothing circuit, thereby enabling on / off control without an auxiliary power supply.