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Time Delay Circuit: 5A Output from Low Voltage Batteries
Description
Within this circuit, a LM339 quad voltage comparator is deployed to establish a time delay and manage a substantial current output at a reduced voltage level. Approximately 5 amps of current can be achieved utilizing a pair of fresh alkaline D batteries. Three of the comparators are connected in parallel to power a medium-power PNP transistor (2N2905 or similar) which, in turn, drives a high-current NPN transistor (TIP35 or similar). The fourth comparator is utilized to generate a time delay after the normally closed switch is opened. Two resistors (36K and 62K) are employed as a voltage divider, applying roughly two-thirds of the battery voltage to the (+) comparator input, amounting to approximately 2 volts. The delay period following the switch opening will be roughly one time constant utilizing a 50uF capacitor and a 100K variable resistor, or about (50u * 100K) = 5 seconds. The delay duration can be lessened by adjusting the resistor towards a smaller value or employing a smaller capacitor. Extended durations can be realized with a larger resistor or capacitor. To operate the circuit on elevated voltages, the 10 ohm resistor should be increased proportionally, (4.5 volts = 15 ohms).
Circuit diagram
