Power-On Time Delay Relay
Here's a power-on time delay relay 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. The 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.
Power-On Time Delay Relay
Title: Power-On Time Delay Relay
electronic circuit
Source: unknown
Published on: 2007-07-21
Reads: 807
Print version:
Other electronic circuits and schematics from Power
-
Fuse Monitor / Alarm
-
Self-powered Fast Battery-Tester
-
0-50V 2A Bench power supply
-
Constant Current Battery Charger
-
Voltage Inverter
-
Ni -Cd Batteries Charger
-
Solar charger for lead-acid batteries
-
High Current Power Supply
-
Variable 3 - 24 Volt / 3 Amp Power Supply
-
LASER Power Supply