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The circuit below can
switch up to 4 amps of current with a peak voltage up to 20v. It is fully
isolated using two inexpensive red LEDs. One LED forms a red light source, which
illuminates a second red LED. The circuit takes advantage of the 1.5v
produced by super bright red LEDs when illuminated with red light. The
voltage produced by one red is routed to two n-channel FETs, configured in a
bi-directional switch circuit. The two FETs selected have a low gate-source
threshold voltage, which allows them to turn on hard from the 1.5v from the red
LED. The bi-directional configuration allows the circuit to switch both AC
and DC power. Using quality super bright red LEDs, the circuit will switch
on fully with only 5ma of LED current.
Click on Drawing Below to view PDF version of Schematic
