Has anybody tried using electric double layer capacitors for the filter capacitor in a power supply?
I found I can get a hold of ten 4.7 F, 2.3 V low resistance super caps for around $30. I figured I would try building a +-10 V power supply with these babys. If I put five of them in series for each rail, it would be an effective capacitance or around 1 F.
I got this idea searching through the old messages. Some guy built a power supply using many 1000 uF capacitors in parallel to achieve something like 50,000 uF. It looked like he had a hundred capacitors in there.
I found I can get a hold of ten 4.7 F, 2.3 V low resistance super caps for around $30. I figured I would try building a +-10 V power supply with these babys. If I put five of them in series for each rail, it would be an effective capacitance or around 1 F.
I got this idea searching through the old messages. Some guy built a power supply using many 1000 uF capacitors in parallel to achieve something like 50,000 uF. It looked like he had a hundred capacitors in there.
Probably not a good idea... supercaps are an oddball. They are really more like a battery than a cap. Read the specs on them... you will see that ther are limits on charge current etc... Another way of saying it: "The ESR is VERY high".
All caps have ESR... Equivalent Series Resistance. So, every time you plop a cap in a circuit you are actually adding a resistor too. For filtering, you want ESR as low as possible... the opposite of a "super-cap".
These things are finding new applications all the time... mostly where people are trying to replace lithium batteries to keep chip memories alive etc...
For audio PS filtering, look for "low ESR". Then bypass close to the individual circuits with film/foil.
All caps have ESR... Equivalent Series Resistance. So, every time you plop a cap in a circuit you are actually adding a resistor too. For filtering, you want ESR as low as possible... the opposite of a "super-cap".
These things are finding new applications all the time... mostly where people are trying to replace lithium batteries to keep chip memories alive etc...
For audio PS filtering, look for "low ESR". Then bypass close to the individual circuits with film/foil.
The local bypass caps stamp out the last little bits of noise right at the point use.
From your PS to your individual circuit blocks is a bit of inductance and resistance and also the potential for noise pickup. So, adding a bypass close to the circuit block is like adding another L/C or R/C stage to the PS. Not always neccesary, by any means.
The "secret" is that certain types of caps only behave truely like caps at certain frequencies... high frequencies skip right over electrolytics.
As an example... you might have 100uf (low ESR) at the PS... and then put a 0.1 - 1.0 uF film foil, or even ceramic, RIGHT across the power pins of an op-amp. The op-amp gets a supply of power free from inductance and behaves better...
From your PS to your individual circuit blocks is a bit of inductance and resistance and also the potential for noise pickup. So, adding a bypass close to the circuit block is like adding another L/C or R/C stage to the PS. Not always neccesary, by any means.
The "secret" is that certain types of caps only behave truely like caps at certain frequencies... high frequencies skip right over electrolytics.
As an example... you might have 100uf (low ESR) at the PS... and then put a 0.1 - 1.0 uF film foil, or even ceramic, RIGHT across the power pins of an op-amp. The op-amp gets a supply of power free from inductance and behaves better...
Back of the envelop calculations will show that they are definitely the wrong part for the job. Electrolytics are what you need and what people always use. Filter cap values are measured in milli farads, ripple current ratings in amps or tens of amps, and voltages in 10's of volts.
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