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Circuits designed by David Johnson, P.E.
Last Updated on:
Thursday, March 04, 2010 04:18 AM
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Relay
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Bidirectional Solid State
Relay
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. |
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Click on Drawing Below
to view PDF version of Schematic |
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Master Schematic
Category List - David A. Johnson, P.E.
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