Hello,

I tried looking for a capacitor with the following specs and nothing so far:

- 100uF or bigger
- less than 1 milli Ohm ESR
- Something that can filter out 1 MHz (Mega Hertz) or more switching frequency...

Thanks

Hello,

I tried looking for a capacitor with the following specs and nothing so far:

- 100uF or bigger
- less than 1 milli Ohm ESR
- Something that can filter out 1 MHz (Mega Hertz) or more switching frequency...

Thanks

- less than 1 milli Ohm ESR

That might be difficult. Digikey (which carries a ship-load of parts) shows **nothing** at 1m Ohm and only a few 2m Ohm high-price non-stock capacitors. Where is that requirement coming from? Maybe there's a work-around.

- Something that can filter out 1 MHz (Mega Hertz) or more switching frequency...

A capacitor by itself isn't a filter. You need a series resistance or inductance. Then you can calculate the "loss" at 1MHz. Of course there is alway some effective resistance, but you don't often know what the that resistance is and sometimes it's not constant.

In a power supply application (where there is a diode or something acting like a diode), you can can calculate/estimate the load resistance. High-frequency high-current pulses can *charge* the capacitor quickly, and the capacitor isn't very effective at filtering those out. But the capacitor *discharges* more slowly into the load, and **capacitor-only filtering can be effective.**

**There are no perfect filters.** Assuming this is a power supply, there will be *some* 1MHz noise on the DC output.

In most low-power applications, 100uF is going to knock-down that noise to an acceptable level. 100uF is "huge" at 1MHz. If you know the load resistance (or current) and the maximum acceptable noise levels, you could make a calculation. But there are always unknowns, so you'd still have to measure the results.

At very-high frequencies, electrolytic capacitors stop "acting like" capacitors, and you need a ceramic (or other) capacitor in parallel. But at 1MHz, your are *probably* still OK.

FardinB:

Hello,I tried looking for a capacitor with the following specs and nothing so far:

- 100uF or bigger
- less than 1 milli Ohm ESR
- Something that can filter out 1 MHz (Mega Hertz) or more switching frequency...
Thanks

You may need to parallel them to get this sort of spec. 10 10uF high-spec ceramics in parallel perhaps?

Could be cheaper too.