JPH0347065B2 - - 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, so the required number of thyristor elements are connected in series and used for high voltage applications. 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 10. This ignition drive circuit includes an ignition power source 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, and a plurality of light emitting elements 4 such as light emitting diodes connected in series. It consists of an ignition amplifier 2 that receives light from a light emitting element and generates an ignition pulse. That is, only when the transistor 5 is in an on state, a current flows through the light emitting element 4 to emit light, and the light is propagated to the ignition amplifier 2 by the light guide 3 to generate a ignition pulse.

However, in such a conventional thyristor firing drive circuit, as the number of light emitting elements 4 connected in series increases, the power supply voltage increases, which is undesirable. The value of the current flowing through the light emitting element 4 tends to be higher than the power supply voltage because the voltage drop across the current limiting resistor 6 is increased in order to avoid fluctuations due to variations in the voltage drop of the element as much as possible. Furthermore, even one light-emitting element 4 connected in series has an open failure (open failure).
When this occurs, the current circuit is cut off, causing the other light emitting elements to stop emitting light and causing the inconvenience that all the thyristor elements 1 do not fire. To avoid such inconvenience, there is a method of connecting all the light emitting elements 4 in parallel, but since it is necessary to insert a current limiting resistor in series with each light emitting element 4, not only does it require a large amount of power, but the wiring becomes complicated. . 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 the ignition reliability by connecting a protection circuit to each thyristor element and passing current through the light emitting element via a current transformer. The present invention provides a thyristor ignition drive circuit that can perform the following steps.

The present invention will be explained below based on an embodiment shown in FIG. According to this invention, as shown in FIG.
The primary windings 81 of these current transformers 8 are connected in series and connected to the ignition power supply 7, and the secondary windings 8
Each light emitting element 4 is connected to 2. Further, according to the present invention, the cross-sectional area of the iron core of the current transformer 8 is set to a value sufficient for the ignition pulse width, but is not made larger than necessary. That is, when one light-emitting element 4 has an open failure, most of the voltage of the ignition power supply 7 is applied to the primary winding 81 of the current transformer 8 corresponding to that light-emitting element 4, but the application of this voltage prevents the change. The size of the cross-sectional area of the iron core is selected so that the iron core of the flow vessel 8 is saturated instantly. Further, when the voltage between the anode and cathode of each thyristor element 1 reaches a predetermined value higher than the operating voltage and lower than the breakdown voltage, an ignition pulse is supplied to the gate pole of the thyristor element 1. A protection circuit 9 is connected to make the circuit conductive.

Therefore, the primary winding 81 and the secondary winding 8 of the current transformer 8
By changing the ratio of 2, the impedance seen from the power supply side can be freely set, and there is no need to increase the power supply voltage regardless of the increase in the number of series-connected light emitting elements 4. In addition, by selecting the cross-sectional area of the core of the current transformer 8 as described above, the core of the current transformer 8 connected to the light emitting element 4 that has an open failure becomes saturated instantaneously, which is equivalent to a short circuit state, and other transformers Since current normally flows through the current flow device 8, the light emitting elements other than the light emitting element with the open failure operate normally.

The light-emitting element 4 with an open failure does not emit light and therefore no firing pulse is generated from its ignition amplifier 2. However, since the protection circuit 9 is connected to the thyristor element 1, the light-emitting element 4 with an open failure
Immediately when the voltage between the anode and cathode of the thyristor element 1 corresponding to the thyristor element 1 reaches the predetermined value, an ignition pulse is generated from the protection circuit 9, and eventually all the thyristor elements 1 become conductive.

Therefore, according to the present invention, even if the number of light emitting elements connected in series increases, there is no need to increase the power supply voltage.
Even if a light-emitting element has an open failure, the other light-emitting elements operate without any abnormality, and the thyristor element corresponding to the light-emitting element that has an open failure is also made conductive by the protection circuit, so the reliability of ignition of the thyristor element is lower than before. You can get a much better effect than the previous one.

[Brief explanation of drawings]

Fig. 1 is a wiring diagram showing a conventional ignition drive circuit for cascade-connected thyristors, and Fig. 2 is a wiring diagram showing an embodiment of the present invention, which is a thyristor ignition drive circuit using a current transformer. The same reference numerals in the figures 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 current transformer, and 9 is a protection circuit.

Claims (1)

[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 these light-emitting elements are caused to emit light by an ignition power source. Further, in the thyristor ignition drive circuit configured to apply an ignition signal from the light emitting element to a corresponding thyristor element, a current transformer is provided corresponding to each of the thyristor elements, and a current transformer is provided for each of the thyristor elements. Primary windings are connected in series and connected to the ignition power source, a light emitting element corresponding to each of the thyristor elements is connected to each secondary winding, and each current transformer is connected to the secondary winding. In the event of an open failure of the light emitting element, the iron core is saturated by receiving the voltage of the ignition power supply, and furthermore, 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 in that a protection circuit is connected to each thyristor element to make the thyristor element conductive.