Can be added to any battery-operated device to eliminate unnecessary running down of costly batteries when someone forgets to tum switch off manually. Circuit shown gives operating time of about 10 hours ,permitting use of equipment for full working day without interruption. Normal operation can be restored after shut-off byturning manual switch off and then on again. When circuit has switched off, only battery drain is current through 10-megohm resistor R1 and leakage through transistors. Time of switch-off can be changed by altering C2 or R7. Tr1 and Tr2 are 2N4061, BC478, or similar PNP silicon; Tr3 is 2N3053, BC142, or similar medium-power NPN silicon; Tr4 and Tr5 are 2N3819; D1 is any small silicon diode; R6 is 4.7K for 9-V or 12-V battery, and 10K for 15-V to 27-V battery. R2 is chosen to suit working current and battery voltage; suitable value is 15Vb/Iout.-D, T. Smith, Automatic Battery Switch-Off Circuit, Wireless World, April 1976, p 76.
Required Field 
