Hello
From: http://www.talkingelectronics.com/projects/TheTransistorAmplifier/TheTransistorAmplifier-P2.html

I've built the following circuit:

In fact I used a 200K ohm resistor instead of 100K and a 1000uF capacitor and I had a delay time of about 3.5 minutes.

The problem is when the main power off the 1000uF capacitor maintained its charge for long time and if the main power returned the circuit is ON immediately without any delay. How to discharge the capacitor?

Thank you very much

 

Hello
From: http://www.talkingelectronics.com/projects/TheTransistorAmplifier/TheTransistorAmplifier-P2.html

I've built the following circuit:

In fact I used a 200K ohm resistor instead of 100K and a 1000uF capacitor and I had a delay time of about 3.5 minutes.

The problem is when the main power off the 1000uF capacitor maintained its charge for long time and if the main power returned the circuit is ON immediately without any delay. How to discharge the capacitor?

Thank you very much

You could try a schottky diode across the 100K resistor with the anode to the + of the cap.

 

You could try a schottky diode across the 100K resistor with the anode to the + of the cap.

Yes
excellent
I try it and the cap. dischaged very fast
thank you very very much

 

This should work.

 

Even better; ditch the Darlington and replace it with a regular NFET (not logic level); That makes it possible to use a much smaller timing capacitor, and a much higher value for the timing resistor (now 100K). You can eliminate the 330K and the other resistor tied to the base of the Darlington, too.

 

Hello
From: http://www.talkingelectronics.com/projects/TheTransistorAmplifier/TheTransistorAmplifier-P2.html

I've built the following circuit:

In fact I used a 200K ohm resistor instead of 100K and a 1000uF capacitor and I had a delay time of about 3.5 minutes.

The problem is when the main power off the 1000uF capacitor maintained its charge for long time and if the main power returned the circuit is ON immediately without any delay. How to discharge the capacitor?

Thank you very much

Just put a diode in parallel with the 100k resistor - pointing upwards so its reverse biased when the capacitor is charging. When you switch off and the supply rail falls, any voltage left on the capacitor forward biases the diode and discharges through the other circuit elements.