Circuits designed by David Johnson, P.E.
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Low Voltage Latch Circuit
February 28, 2013
A Discover Circuits
visitor wanted a simple on/off latch circuit which can turn on and off power to a
small motor. The kicker was that he wanted to power the circuit and the motor
from a single 1.2v NiMH
battery cell. Texas Instruments comes to the rescue with
their family of low voltage single gate ICs. Specifically the SN74AUP1Q14
Schmitt trigger inverter will operate down to 0.8v and lower. When used with a
good NPN transistor, the circuit below works quite nicely.
With each press of a small pushbutton switch, the circuit will latch in
either the on or off state. When on, the output turns on NPN transistor which has a
high gain and a very low saturation voltage. The transistor can handle a higher
current than needed by the motor but I would suggest liming the current to about 200ma.
on Drawing Below to view PDF version of Schematic
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