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Suitability of power FET in circuit

Discussion in 'Electronic Basics' started by Phideaux, Jan 14, 2004.

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  1. Phideaux

    Phideaux Guest

    I need to switch on a circuit containing 2 incandescent bulbs to blink
    in unison. The flasher is of the automotive type, with 12V connected
    to it. The FET would be placed between the flasher and the two bulbs,
    completing the circuit when activated. Each bulb takes slightly less
    than 2 amps while in the steady "on" state, but as we know the surge
    amperage to turn on the bulb is considerably higher. The FET would
    basically be in a 50% duty cycle while the circuit is active, which
    will not be that often. Can an FET handle the job, or should I just
    drive a relay and be done with it?
  2. A 20 amp surge is no problem at all for many cheap TO220 case fets.
    You may want to use ones that have internal over voltage protection
    for the gate, or add a zener. A 15 volt zener gate to source and a 1k
    resistor in series with the gate signal should make it pretty iron

    Digikey has hundreds of usable devices, many for under a dollar.
    Anything with an on resistance well under about .2 ohms and 30 volts
    rating should work with no heat sink.
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