JPS61293164A - Protection circuit for short-circuit - Google Patents

Abstract

PURPOSE:To perform the short-circuit protection of a transformer positively by giving a decision that coils are found short when in a multi-coiled transformer the output of the subsidiary coil is abnormal although that of the main coil is normal. CONSTITUTION:In a transformer 9 with two or more coils, a positive output A of the first coil (the coil on the main winding side) 12 and the negative output inversion B of an output B of an output terminal 11 of the second coil (subsidiary coil) are inputted to NAND element 14. When AND of these becomes '1', it is decided that the coil is found short and the necessary stopping signal STP is outputted. In this way, the malfunction can be prevented as STP signal becomes valid only when the output A is normal and the output B is abnormal.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to short-circuit protection for transformers, and particularly to a short-circuit protection circuit suitable for short-circuit protection of windings of transformers having a plurality of windings. .

[Background of the invention]

As a conventional short-circuit protection circuit, the one shown in FIG. 4 is generally known. In the figure, 1 is a rectifier circuit, 9 is a switching transformer, 10 is an output transistor, and 8 is a square wave oscillation circuit.During normal operation, it is at -"1", and is switched by the output transistor 10, and the output is DC output is supplied to terminal 11. If the output terminal 11 is now short-circuited, the penalty Φ = “0#” will be generated in the square wave oscillation circuit 8.
oscillation stops, direct current output is prohibited, and protection is provided in the event of a short circuit.

However, in the circuit shown in FIG. 4, when the circuit is started immediately after the power switch 3 is turned on, a period corresponding to the period Φ="0" occurs, which may make startup difficult. Therefore, the time constants of the output terminal 11, the oscillation circuit power supply winding 12, and the square wave oscillation circuit 8 must be appropriately selected to continue oscillation at startup.

Note that related devices of this type include, for example, Japanese Utility Model Publication No. 58-34496.

[Purpose of the invention]

It is an object of the present invention to provide short-circuit protection for the transformer by reliably detecting a change in state when the main winding of the transformer is normal but the subordinate winding is short-circuited. The purpose is to provide circuits.

[Summary of the invention]

In the present invention, only when the output voltage of the main winding is normal and the output voltage of the subordinate winding is abnormal, it is assumed that the winding is short-circuited, and the short-circuit protection circuit is prevented from malfunctioning, and the winding An abnormality in the output voltage of the winding is determined by directly detecting the presence or absence of the output voltage of the winding, and the short circuit protection operation is ensured.

[Embodiments of the invention]

FIG. 1 shows an embodiment of a short circuit protection circuit according to the present invention.

In the present invention, the inverter 13 and the NAND gate 14 obtain the AND of the output A of the winding 12 on the main winding side and the negative output (■) of the output B of the winding output terminal 11 on the dependent winding side. This is considered a surface signal.

With this configuration, 5TP=A*B and the main winding side starts normal operation, only when the output A of the main winding side is normal and the output B of the subordinate winding side is changed. STP
Since the signal becomes valid, it can be assumed that the winding is short-circuited, and malfunction of the short-circuit protection circuit can be prevented.

FIG. 3 shows an embodiment of the winding short-circuit state detection means according to the present invention. The emitter and base of a detection transistor 17 are connected to both ends of the rectified output of the winding 15 via a resistor 16, and the output B of the winding 15 is obtained from the connection point with the resistor 18 on the collector side.

With such a configuration, the short circuit state of the winding 15 can be directly detected, and the operation becomes reliable.

〔Effect of the invention〕

As explained above, by using the AND output of the positive output of the main winding and the negative output of the dependent winding as the short circuit detection signal, it is possible to reliably prevent malfunction of the short circuit protection circuit, and also By directly detecting the output voltage change of the target winding, short circuit protection can be performed reliably.
The practical effects are great.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the short circuit protection circuit according to the present invention, FIG. 2 is a circuit diagram showing conventional short circuit detection means, and FIG. 6 is a circuit diagram showing short circuit detection means according to the present invention. FIG. 4 is a circuit diagram showing a conventional short circuit protection circuit. 1... Rectifier circuit 8... Square wave oscillation circuit

Claims (1)

[Claims] In a transformer having one or more sets of windings, the AND output of the positive output of the first winding and the negative output of the second winding is "1". A short-circuit protection circuit characterized in that a short-circuit state of a second winding is detected by detecting this. 2. The short-circuit protection circuit according to claim 1, wherein the emitter and base of a transistor are connected to both ends of the winding whose short-circuit condition is to be detected, and the output of the winding is obtained from the collector.