# How do I modify the final current equation so that...?

Discussion in 'General Electronics Chat' started by PG1995, Oct 30, 2011.

1. ### PG1995 Thread Starter Active Member

Apr 15, 2011
753
5
Hi

Please have a look on the attachment. My main question is at the end. How do I modify the final current equation so that it adjusts for the discharging up to only 27V? Please help me. Thank you.

The answer given is: 4.5 + 5/6 e^(-t/0.15) mA

Regards
PG

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2. ### Ron H AAC Fanatic!

Apr 14, 2005
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The time constant is correct, but I can't figure out where that answer came from.
The cap's initial voltage is 32V, and it discharges into 27V through 1.5kΩ. Therefore, the current at t(0)+ is (32-27)/1.5k. Armed with this knowledge, you should be able to write an equation that expresses the current as a function of time.

3. ### edisonli New Member

Oct 31, 2011
1
0
tough question to me

Apr 15, 2011
753
5
5. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
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PG1995 likes this.