SCR_CIRCUIT_WITH_SELF_NTERRUPTING_LOAD

Published:2009/7/8 23:00:00 Author:May | From:SeekIC

A self-interrupting device connected to a volt-age source functions as a switch that repeatedly opens and closes; therefore, the circuit does not latch in the normal way, so the alarm operates only as long as S1 is closed. Because of the inductive nature of that type of load, a damping diode (D1) must be wired across it. The circuit can be modified to provide a self-latching action simply by wiring a 470-Ω resistor in parallel with the alarm. The circuit latches because the anode current of the SCR does not fall to zero when the alarm self-interrupts, but to a value that is determined by the value of the R3. The circuit can be unlatched by pressing S2, thereby enabling the anode current to fall to zero when the alarm self-interrupts.



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