Indicator lamp test circuit utilizing bidirectional thyristor switching

摘要

A circuit is provided for test and operation of indicator lights wherein multiple lights may be tested simultaneously by pushing one button and closing one set of normally open contacts and the individual indicator lights are operated from a circuit utilizing a self- triggering bidirectional thyristor. The test pushbutton and the indicator operating signal circuit operate at a higher voltage, such as 120 volts ac, and the indicator lamp is operated at a low voltage, such as 6 volts ac, providing safety and allowing use of inexpensive incandescent indicator bulbs. One indicator transformer is required for each indicator light. A diode is provided in the test circuit on the high voltage side of each of the indicator transformers to permit a test signal to activate the indicator lamps without affecting the rest of the circuit. The diodes in the test circuit permit only unidirectional current to flow therethrough. The operating signal circuit is also connected to the high voltage side of each transformer, in parallel with the test circuit. A bidirectional thyristor is used to switch the indicator circuit on lighting the indicator lamp and providing circuit isolation. The bidirectional thyristor is connected so to be self-triggering and when current flows in the line to which the thyristor is connected the thyristor is triggered on energizing the transformer and lighting the indicating lamp. The lumination of the indicator lamps when activated through the test circuit is less than the lumination when activated through the normal indicator signal circuit.