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Power off timer circuit

DonMuncy

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Jul 14, 2013
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I am almost electronically illiterate, but I am working on a circuit to keep the dome light in my airplane on for 5 minutes or so after the power to it is turned off.
I have assembled the attached circuit, but can only make the timer run for about a minute. My circuit is a 12v circuit, uses a 4700 mf capacitor and about 27K resistance.
I tried adding an additional 2000mf capacitor in parallel with the larger one, but it only increased the time by about 15 seconds.
Adding about 5K more resistance causes the circuit to not function.
Any ideas as to how to increase the time to 5 or 6 minutes without exceeding my capabilities. I understand relays, resistors, diodes, and about half understand transistors.
any help is appreciated.
Don
 

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  • Timer circuit.doc
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