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Suitability of power FET in circuit

P

Phideaux

Jan 1, 1970
0
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?
 
J

John Popelish

Jan 1, 1970
0
Phideaux said:
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?

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
clad.

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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