>Hello all,
>I have a circuit (it contains a pic) which has a couple of rather large
>aluminum electrolytic capacitors (2200uF) as supply filters. the problem
>is that when the circuit is turned off, the charge takes a little while to
>dissipate (i have a power on led in series with a 1K resistor across the
>supply lines) and while its dissipating, the pic among other things is
>still funtioning. I am worred that the pic might end up in one of my
>routines which, for example writes to an I2C EEPROM, and corrupt the data
>there. so what i need is a way to disipate the capacitor reletively
>quickly after power down. I was thinking of putting a diode in paralel in
>the wrong direction (anode to gnd, cathode to vcc) but i dont think this
>will work, since the charge in the capacitor is polarized. I hope someone
>has an idea.. thanks agian

     I am no expert, but probably the best way to do this is to get the PIC
to stop doing stuff when the power supply goes away, a brownout circuit
which is quite common would work well, but if instead you want to instead
make sure the PIC continues the last required operation before power is
lost, you could tie one input pin to the supply before the filter capacitor
(of course some cleaning would be required). The PIC would then be able to
tell if power is going to be lost very soon and can do the appropriate
operation and shut down before power is lost. Hope this made sense, TTYL