LIGHT_FLASHER

Published:2009/7/13 11:47:00 Author:May | From:SeekIC

Shown here is a simple flasher circuit. With the component values shown, the flash rate is approximately once per second. The incandescent-lamp load glows at half brightness for about one-third of the total flasher period and is off for the remaining two-thirds. Electrolytic capacitor C1 charges during the positive half-cycle of the ac waveform through R1, R3, and D2. When the voltage across the capacitor reaches the break-over voltage of the silicon asymmetrical switch (SAS1), the capacitor starts to discharge through R2, SAS1, Q1, R4, and the triac. Emitter follower Q1 is driven by the discharge current from C1, and it, in turn, provides gate drive for the triac. Thus, the triac conducts and the light glows while C1 discharges. The lamp goes dark when C1 is depleted of charge and remains dark until the ac power waveform goes positive again and charges the capacitor sufficiently. The triac should be triggered into conduction by a gate current of no more than 5 mA. The flash rate can be varied by changing the value of capacitor C1. Using more capacitance results in a slower flash rate, and less capacitance results in a faster flash rate.



Reprinted Url Of This Article:
http://www.seekic.com/circuit_diagram/LED_and_Light_Circuit/LIGHT_FLASHER.html

Print this Page | Comments | Reading(3)