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More  Driver Circuits, Switches, Latching Circuits, Relays

ON/OFF SWITCH WITH LATCHING RELAY (December 24, 2009)


The circuit below switches AC or DC power to a load using an ultra low power 3v latching relay with two coils.  The relay can handle about 10 Amps of current, up to 250vac.  Each time the small pushbutton is pressed, the circuit either latches the relay contacts closed or unlatch them open.  The 3v powered circuit uses a single 74HC14. This device contains six Schmitt trigger inverters in the one 14 pin package.  Two inverters form a flip/flop circuit.  Each time the pushbutton is pressed, the circuit changes state and stays in that state until the button is pressed again.  With each state change, a 25ms latching or unlatching pulse is produced and is routed to the correct relay coil.  The coil resistance is about 45 ohms so about 70ma of current is drawn from the 3v battery for each relay pulse.  The average power is so low that the circuit can operate for many years on one set of batteries.  I would suggest using two AA or AAA alkaline cells.

Click on Drawing Below to view PDF version of Schematic

On/Off Switch with Latching Relay designed by Dave Johnson, P.E.

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