Tuesday, October 25, 2011

Circuit » Home » » » » » » » » » » » » » SIMPLE SWITCH TIME DELAY CIRCUIT DIAGRAM

SIMPLE SWITCH TIME DELAY CIRCUIT DIAGRAM

SIMPLE SWITCH TIME DELAY CIRCUIT DIAGRAM

This Switch On Time Delay circuit should work with most any 12 volt DC relay that has a coil resistance of 75 ohms or more. The 10K resistor connected across the supply provides a discharge path for the capacitor when power is turned off and is not needed if the power supply already has a bleeder resistor.The circuit that takes advantage of the emitter/base breakdown voltage of an ordinary bi-polar transistor. The reverse connected emitter/base junction of a 2N3904 transistor is used as an 8 volt zener diode which creates a higher turn-on voltage for the Darlington connected transistor pair. Most any bi-polar transistor may be used, but the zener voltage will vary from about 6 to 9 volts depending on the particular transistor used. Time delay is roughly 7 seconds using a 47K resistor and 100uF capacitor and can be reduced by reducing the R or C values. Longer delays can be obtained with a larger capacitor, the timing resistor probably shouldn't be increased past 47K. 

1 comment:

  1. Hi. Should the Capacitor voltage be as close to 12v as possible, or should be be either higher of lower?

    ReplyDelete