JPH0344501B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a firing drive circuit for a thyristor circuit including a plurality of cascade-connected thyristor elements.

Thyristor elements conventionally used in high-voltage circuits (for example, AC/DC converters, inverters) have a small withstand voltage value, and therefore the required number of thyristor elements are connected in series. FIG. 1 shows a conventional thyristor firing drive circuit, in which a plurality of thyristor elements 1 are connected in series, and a firing pulse is sent to the gate pole of each thyristor element by a firing drive circuit 12. This ignition drive circuit includes an ignition power supply 7, a current limiting resistor 6, a transistor 5 for performing a switching action, a plurality of light emitting elements 4 such as light emitting diodes connected in series, provided corresponding to each thyristor element 1, It consists of an ignition amplifier 2 that receives light from this light emitting element and generates an ignition pulse. That is,
Only when the transistor 5 is in the on state, a current flows through the light emitting element 4 to emit light, and the light is propagated by the light guide 3 to the ignition amplifier 2 to generate a ignition pulse.

However, in such a conventional thyristor firing drive circuit, even if an open failure occurs in one light emitting element 4, there is no circuit through which current can flow, so the other light emitting elements 4 stop emitting light, and all the thyristor elements 1 The inconvenience occurs that the ignition does not occur. In order to avoid this, there is a method of connecting all the light emitting elements 4 in parallel, but this is not preferable because it requires a current limiting resistor to be inserted in series with each light emitting element 4, which requires a large amount of power. As described above, conventional ignition drive circuits have the drawbacks of extremely low ignition reliability or extremely uneconomical performance.

This invention eliminates the drawbacks of the conventional circuit as described above, and greatly improves ignition reliability by connecting a protection circuit to each thyristor element and connecting a nonlinear element in parallel with each light emitting element. The present invention provides a thyristor ignition drive circuit that can perform the following steps.

A description will be given below based on an embodiment shown in the drawings.

FIG. 2 shows an embodiment of the present invention. According to the present invention, each light emitting element 4 such as a light emitting diode is
A nonlinear element 8 having a high impedance at a voltage lower than the forward direction (positive direction) voltage drop value and a low impedance at a voltage higher than the forward direction (positive direction) voltage drop value is connected to the nonlinear element 8. The operation when using such an element 8 is that when the light emitting element 4 is normal, that is, when current flows and emits light, this current does not flow to the nonlinear element 8, so the operation is no different from that shown in Fig. 1. Never. However, when the light emitting element 4 has an open failure, the circuit tends to turn off, and the voltage of the ignition power source 7 tries to be applied to the nonlinear element 8 connected to the light emitting element 4 with the open failure, but as mentioned earlier, the voltage As the impedance increases, the impedance immediately decreases, so the voltage drop across it decreases, resulting in the same state as a short circuit. Therefore, the light emitting element 4 with the open failure does not emit light, but the other light emitting elements 4 emit light without any abnormality.

Furthermore, according to the present invention, a firing pulse is supplied to the gate pole of each thyristor element 1 when the voltage between its anode and cathode reaches a predetermined value higher than its operating voltage and lower than its breakdown voltage. a protection circuit 11 that makes the thyristor element 1 conductive;
is connected. Therefore, even if the light emitting element 4 with an open failure does not emit light, its ignition amplifier 2
Since the protection circuit 11 is connected to the thyristor element 1 even if the ignition pulse is not generated from the
As soon as the voltage between the anode and cathode of the thyristor element 1 corresponding to the light emitting element 4 which has an open failure reaches the predetermined value, an ignition pulse is generated from the protection circuit 11, and eventually all the thyristor elements 1 become conductive. Therefore, even if an open failure occurs in the light emitting element 4, conduction control of all the thyristor elements 1 can be performed without any problem.

FIG. 3 shows an example in which a constant voltage diode 9 is used as the nonlinear element 8 in FIG. 2, and FIG. 4 shows an example in which a rectifying diode 10 is used. The reason why two diodes 10 are used in FIG. 4 is to adjust the value of voltage drop, that is, the impedance mentioned above, and the number of diodes 10 connected in series may be determined as appropriate. Note that FIGS. 3 and 4 show the light guide 3,
Although the ignition amplifier 2, the thyristor element 1 and the protection circuit 11 are not shown, they have exactly the same construction as in FIG.

As described above, according to the present invention, even if an open failure occurs in a light emitting element, the other light emitting elements operate without any abnormality, so that the reliability of ignition is greatly improved compared to the conventional one.

Therefore, according to the present invention, it is possible to obtain an extremely reliable thyristor ignition drive circuit having the above-mentioned advantages using an extremely simple method.

[Brief explanation of drawings]

Fig. 1 is a wiring diagram showing a conventional firing drive circuit of cascade-connected thyristors, Fig. 2 is a diagram showing an embodiment of the present invention and shows a constituent circuit in which nonlinear elements are connected, Fig. 3, and FIG. 4 is a diagram showing a specific embodiment of the circuit shown in FIG. 2, and the same reference numerals in the figure indicate the same parts. In the figure, 1 is a thyristor element, 2 is an ignition amplifier, and 4
is a light emitting element, 7 is an ignition power source, 8 is a nonlinear element, 1
1 is a protection circuit.

Claims (1)

[Scope of Claims] 1. An ignition drive circuit for a plurality of cascade-connected thyristor elements, in which a plurality of light emitting elements provided corresponding to each thyristor element are connected in series and connected to an ignition power supply, In the device that applies the firing signal from the light emitting element to the corresponding thyristor element, each light emitting element has a high impedance at a voltage lower than its forward voltage drop value, but has a low impedance at a voltage higher than the forward voltage drop value. Nonlinear elements having impedance are connected in parallel, and each thyristor element is provided with a protection circuit that makes the thyristor element conductive when the voltage between the anode and cathode of each thyristor element reaches a predetermined voltage higher than its operating voltage and lower than its breakdown voltage. A thyristor firing drive circuit characterized by being connected to. 2. The thyristor firing drive circuit according to claim 1, wherein the nonlinear element is a constant voltage diode. 3. The thyristor firing drive circuit according to claim 1, comprising one nonlinear element or a plurality of rectifying diodes connected in series.