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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. |
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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.
Driver Circuits,
Switches, Latching Circuits,
Relays |
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