Solid_state_time_delay

Published:2009/7/22 3:48:00 Author:Jessie | From:SeekIC

This circuit shows the basic UJT building block (Fig. 9-1), which is used to provide a time-delay function. The circuit is similar to that of Fig. 9-13, except that the mechanical relay is replaced by an SCR (which generally reduces circuit cost). When S1 is pushed, or when a positive-going pulse is applied at point A, SCR#2 turns on and SCR#1 is turned off by CC. With SCR#1 off, the supply voltage is applied to RE, and the circuit begins to time. After a period (determined by the setting of RE), the UJT fires and turns SCR#1 on and SCR#2 off. With the values shown, time delay can be varied from about 1 s to over 2 min.



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