Cap discharge question

Thread Starter

erice1984

Joined Jun 9, 2007
16
what can I do to increase the discharge time of a capacitor

12vdc -> 100k Ohm -> 22uF -> gnd

in 3.5sec cap charges to 9.7v
but takes 10sec to discharge to 800mV

Anyway to make the cap discharge faster than charging or almost at same rate

Thanks
 

hgmjr

Joined Jan 28, 2005
9,029
One way to do it is put a diode in series with a smaller valued resistor and then put this diode/resistor combination in parallel with the 100K resistor so that the diode is reverse biased on charge and forward biased on discharge. That way when in the charge mode the diode is reverse biased and so only the 100K resistor is determining the rate of charge. Now when the discharge mode is selected the diode becomes forward biased and now the second resistor is in parallel with the 100K and so the discharge rate is speeded up.

hgmjr
 

hgmjr

Joined Jan 28, 2005
9,029
Erice1984,

I accidentally reversed the sense of forward-bias and reverse-bias in my recommendation so I corrected it in my earlier reply. I just wanted to let you know.

hgmjr
 

RiG615

Joined Nov 13, 2008
50
Is there a formula to determine the discharge rate??
and how much would the LED affect the discharge time?
how can you make charge/discharge the same time??
 
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