5_min_AC_TIMER

Published:2009/7/14 5:36:00 Author:May | From:SeekIC

This 555-based circuit will power a load for up to 5 minutes, depending on the setting of R1. Note the transformerless power supply made up of C1, C2, D1, and D2. The timer covers 0 to 5 minutes, or a little more, by measuring the time needed to charge C3 through R1, which is adjustable. To switch the ac power to the load, the timer uses a triac (a solid-state ac switch) instead of a relay. In the power supply, the capacitive reactance of C1 limits the current without generating heat. Use a metal-film capacitor for C1, not an electrolytic. Be sure to observe the voltage rating-use a capacitor rated for at least 200 V (preferably 600 V). Zener diode D1 limits the voltage, and D2 and C2 are the rectifier and filter.



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