hello.......

hello to all here.... i am new here... my fren intro me to this forum.... so hope that can make more new frens with the same interest here...

i have a question about capacitor... how can a capacitor supply a negative voltage after it has been charged ??????

yes if its then conected backwards

Use a "charge-pump" IC like an ICL7660 to make a negative supply from a positive one.

oo....

does that mean that there must be an external circuit or device to cause the reversal of capacitor voltage? this question is about a topic regarding the SCR turn off where they actually use a capacitor to provide a negative voltage so that the SCR is reverese biased..... so that is possible with the ways you mentioned is it???

anyway, thanks for the reply....

Re: oo....

chinsoon said:

does that mean that there must be an external circuit or device to cause the reversal of capacitor voltage? this question is about a topic regarding the SCR turn off where they actually use a capacitor to provide a negative voltage so that the SCR is reverese biased..... so that is possible with the ways you mentioned is it???

Click to expand...

It's done using a second SCR, the capacitor is connected between the two SCR's. It works like a bistable, with only one being turned ON at a time, the act of turning the second one ON dischares the capacitor through the other one.