How to discharge the capacitor faster

Just add a resistor to the circuit so that the cap can discharge through the resistor. A 10K resistor will discharge the cap in about 1 second.

vax, 9000

there

about

the

there

power

a new

about 20

sometimes

manually,

faster

These caps are commonplace on PCBs with ICs on them (they are called decoupling caps). You're cap is taking a long time to drop below a certain threshold value because it's capacitance is far too high (RC time constant too high). Usually, 10 - 100nF is the standard for decoupling caps used on digital VCC/VDD inputs. Try 10nf first, if the ripple rejection is not high enough, step it up. I don't suggest using bleeder resistors of any sort until you have exhausted all other possibilities (resistors take up needless PCB real-estate and waste energy).

You are trying to solve the wrong problem. No matter what you use to discharge the capacitor, there will be some discharge time at which you can't re-apply power without a hangup. You should probably take another look at the "voltage-delicate" chipset and figure out why it hangs up during a brown-out. Perhaps the solution is to add a reset-detection chip, commonly used with microcontrollers to hold the chip in reset whenever the voltage is below a certain threshold.

-Robert Scott Ypsilanti, Michigan (Reply through this forum, not by direct e-mail to me, as automatic reply address is fake.)

I believe it can wipe off the weed from the root, but I got to spend an extra reset-detection chip and redraw part of my PCB. Is there any reset-detection chip less than 50 cents each?

Johnson.

there

new

sometimes

address is fake.)

The sad thing is, I tried different capacitors, and only 100uF and 10uF worked. All other capacitors less than 10 uF will still get the delicate chip crazy.

Johnson

The brute capacitor may well be overkill. A much smaller one might suffice with a series resistor, and then a relatively small bleeder can remove the power rapidly. The first thing is to know the power requirements of that chipset. You might also find that an active local regulator is the best solution. Engineer it, don't beat it to death with a shovel.

I suspect that the "voltage-delicate" chipset hangs up during a brown-out, is possibly because the 100uF Cap works like a back-up battery during brown-out. Until the cap get discharged, the chipset will not feel the power cycle, thus it did not perform a reset.

Johnson

there

new

sometimes

address is fake.)

I strongly suggest using the full array of brown-out/monitoring ICs out there to reset "all" major ICs on the PCB. If your PCB has a microcontroller on it, you would probably tie this circuitry in with any watchdog.

If you don't want to go that far, I think the best solution is the have a grace period before you assume all devices are fully reset. Don't just drop the rails and then turn them back on immediately.

I still find the fact that you needed a 100uF to get the ripple rejection job done peculiar. Are there are details of this PCB you can post (possibly a partial schematic)?

"Johnson Liuis"

Don't you have a voltage regulator to remove the ripple?

You need a proper reset circuit. Try Maxim. A cheap op-amp/ comparator can also do a good job. You can use a dual amp for voltage regulation and for reset, try an LM358; the extra current draw of the op-amp will drain the cap faster.

Anybody make a combined voltage regulator/reset/voltage supervisor?

new

sometimes

manually,

As others have said, you're trying to fix the wrong problem. The clue is:

there is a ripple in Power Supply over 0.2V.

You haven't given any details whatsoever concerning your power-supply. If you are really craving assistance then start there. Why be vague with "voltage-delicate chipset", say what it is.

Some questions:

- how are you measuring the ripple? (is it really there)

- what frequency is this ripple?

- what is the ripple like prior to the regulator?

- you are feeding dc into the regulator, aren't you?

- are you sure you are asking the right question?

Checklist:

- The input to the regulator should be filtered and at least 3V or more higher than the regulated voltage (assuming standard regulator etc)

- make sure your pcb layout is not the culprit (ground loops)

Sorry for the serve, I could give you the solution if I didn't have to guess.

Johns> I am dealing with a voltage-delicate chipset which will stop work if there

Mmmm, sounds you are right. I finally found a way to solve the problem with a 1u Cap and a series resistor.

I am using Microsoft Outlook newsreader, not google group, so I cannot find the buttons/links you mentioned. Any suggestion for posting on Microsoft Outlook newsreader?

Johnson