JPH04207314A - Control circuit for switching element - Google Patents

Abstract

PURPOSE:To shorten the minimum on-time to the utmost limit by providing a detection circuit which detects the voltage or current of a snubber capacitor and feeds back it to a control circuit. CONSTITUTION:The voltage of the snubber capacitor 5 is voltage-divided into appropriate voltage by potential division resistors 7, 8, and the level of a detection voltage is decided by a Zener diode 9. When the both terminal voltages of the potential division resistor 8 exceed the Zener voltage of the Zener diode 9, a current flows on a light emitting diode 10, and a light receiving transistor 11 can be kept in an on-state. Thereby, a driving circuit 2 can be kept in an on-operation even when the control circuit 1 issues off-operation output, and when the voltage of the snubber capacitor 5 goes less than the Zener voltage of the Zener diode 9, an off-operation signal is immediately supplied to the driving circuit 2. Thereby, it is possible to shorten the minimum on-time to the utmost limit without performing the off-operation of a switching element 3 when the charge voltage of the snubber capacitor 5 is high.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the operation control and protection of switching elements having snubber circuits.

[Conventional technology]

Conventional switching element control circuits with snubber circuits use snubber circuits to ensure the minimum on-time, as stated in page 123 of OHM, January issue supplement (1987, published by Ohmsha Co., Ltd.). In a control method such as that in which the on-time is set to be a constant time regardless of the state of the on-state, the minimum on-time must be set longer than necessary, which limits the ability of the device to operate at higher frequencies.

Furthermore, if an off signal is applied to the switching element while the snubber capacitor is not sufficiently discharged due to malfunction or the like, the element cannot be protected.

[Problem to be solved by the invention]

The above-mentioned conventional technology has a problem in that the minimum on-time must be long to some extent so that the snubber capacitor can be sufficiently discharged, which is a constraint on higher frequencies.

Furthermore, there is a problem in that the switching element may turn off during the minimum on-time due to the generation of erroneous pulses due to noise or the like, resulting in destruction.

An object of the present invention is to suppress the minimum hair-off time to the necessary minimum.

Another object of the present invention is to prevent the switching element from being turned off during the minimum off time.

[Means to solve the problem]

In order to achieve the above object, the voltage of the snubber capacitor is detected and an off signal is immediately applied when the voltage becomes low.

Furthermore, in order to protect the switching elements, an off signal is not applied when the voltage is high.

[Effect]

The detection circuit allows the control circuit to output an off signal when the snubber capacitor has a low voltage, and prohibits output of the off signal when the snubber capacitor has a high voltage.

Thereby, the control circuit can provide an off signal to the switching element if given permission from the sensing circuit;
The snubber capacitor does not give a false off signal when the voltage is high.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

The voltage of the snubber capacitor 5 is divided into appropriate voltages by a voltage dividing resistor 7 and a voltage dividing resistor 8, and the level of the detection voltage is determined by a Zener diode 9. The signal is isolated by a light emitting diode 10 and a light receiving transistor 11. and fed back to the control circuit.

Now, when the voltage across the voltage dividing resistor 8 is higher than the Zener voltage of the Zener diode 9, a current flows through one light emitting diode 10, and the light receiving transistor 11 is kept in an on state. As a result, even if the control circuit 1 outputs an OFF operation output, the drive circuit 2 remains in the ON operation, and when the voltage of the snubber capacitor 5 becomes lower than the Zener voltage of the Zener diode 9, an OFF operation signal is immediately sent to the drive circuit 2. is given.

As a result, when the charging voltage of the snubber capacitor 5 is high, the minimum on-time can be shortened to the limit without turning off the switching element 3.

〔Effect of the invention〕

According to the present invention, since the minimum on-time can be shortened to the limit, the device can be operated at a higher frequency. Further, it is also possible to prevent the switching element from turning off when the snubber capacitor is at a high voltage due to noise or the like.

[Brief explanation of the drawing]

FIG. 1 shows a circuit diagram of an embodiment of the present invention. 4... Snubber diode, 5... Snubber capacitor. 6... Snubber resistor, 10... Light emitting diode, 1
1... Light receiving transistor. First cause

Claims (1)

[Claims] 1. In order to protect the switching element, in the snubber circuit that has a resistor and capacitor installed in parallel with the switching element, a detection circuit is installed to detect the voltage or current of the snubber capacitor and feed it back to the control circuit. A switching element control circuit characterized by: