Schematics > Oscillators and timers > Low Voltage, High Current Time Delay Circuit
Low Voltage, High Current Time Delay CircuitIn this circuit a LM339 quad voltage comparator is used to generate a time
delay and control a high current output at low voltage. Approximatey 5 amps of
current can be obtained using a couple fresh alkaline D batteries. Three of the
comparators are wired in parallel to drive a medium power PNP transistor (2N2905
or similar) which in turn drives a high current NPN transistor (TIP35 or similar).
The 4th comparator is used to generate a time delay after the normally closed
switch is opened. Two resistors (36K and 62K) are used as a voltage divider
which applies about two-thirds of the battery voltage to the (+) comparator
input, or about 2 volts. The delay time after the switch is opened will be
around one time constant using a 50uF capacitor and 100K variable resistor, or
about (50u * 100K) = 5 seconds. The time can be reduced by adjusting the
resistor to a lower value or using a smaller capacitor. Longer times can be
obtained with a larger resistor or capacitor. To operate the circuit on higher
voltages, the 10 ohm resistor should be increased proportionally, (4.5 volts =
15 ohms).
Low Voltage, High Current Time Delay Circuit
Title: Low Voltage, High Current Time Delay Circuit
Source: unknown
Published on: 2007-07-21
Reads: 570
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