Precision PSU

[soje]

As I understand it, the precision PSU is part of the later dumbles. I have a few questions about this:

- I suppose two 47uF in series reacts faster than one 22uF. Is this right?

- Is there a difference in performance between two 47uF in series, and two 10uF in parallel, as long as voltage rating is observed?

- How would a 22uF with say a 100nF cap in parallel perform compared to this?


Thanks!

soje

[ayan]

As I understand it, the precision PSU is part of the later dumbles. I have a few questions about this:

- I suppose two 47uF in series reacts faster than one 22uF. Is this right?

- Is there a difference in performance between two 47uF in series, and two 10uF in parallel, as long as voltage rating is observed?

- How would a 22uF with say a 100nF cap in parallel perform compared to this?


Thanks!

soje

With the notion that caps in parallel add their values, and in series you need to take the reciprocal of the sum of the reciprocals:

1. Two 47uF in series are equivalent to a single 23.5uF, so that VS 22uF is a bit of a wash

2. Two 47uF in series gives you 94uF and two 10uF in parallel 20uF. Big difference here

3. A 22uF with a 100nF cap in parallel gives you 120uF

Gil

[Structo]

A 100nf cap is .1uf

Unless the nf was a typo a 22uf plus a 100nf would equal 22.1uf.

[ayan]

A 100nf cap is .1uf

Unless the nf was a typo a 22uf plus a 100nf would equal 22.1uf.

Ah, of course! I didn't even see the n instead of u, as nF is non standard in the US -- but it is a perfeclty valid unit nonetheless. The only reason to add a small cap in parallel with a large cap is to, supposedly, smooth things out some.

Gil

[Structo]

Sorry Gil I didn't mean to correct you, I thought maybe it was a typo.

[ayan]

Sorry Gil I didn't mean to correct you, I thought maybe it was a typo.

Oh too late for that now! I didn't even nee the n, buck stops here.

Gil

[heisthl]

2. Two 47uF in series gives you 94uF

Gil

Here's the real typo

[martin manning]

As I understand it, the precision PSU is part of the later dumbles. I have a few questions about this:

- I suppose two 47uF in series reacts faster than one 22uF. Is this right?

- Is there a difference in performance between two 47uF in series, and two 10uF in parallel, as long as voltage rating is observed?

- How would a 22uF with say a 100nF cap in parallel perform compared to this?


Thanks!

soje

With the notion that caps in parallel add their values, and in series you need to take the reciprocal of the sum of the reciprocals:

1. Two 47uF in series are equivalent to a single 23.5uF, so that VS 22uF is a bit of a wash

2. Two 47uF in series gives you 94uF and two 10uF in parallel 20uF. Big difference here

3. A 22uF with a 100nF cap in parallel gives you 120uF

Gil

I think you have another typo there Gil, two 47uf in parallel gives 94uf. Two 47uf in series gives 23.5uf as you said in answer to #1, and that is close to the same (well, within ~20%) as two 10uf in parallel, giving 20uf.

I think the only point in using two larger caps in series is so that a lower voltage rating can be used, lowering the per part cost, at the expense of more parts. I've wondered about the ESR of the two caps in series, paralleled with the balancing resistors against the ESR of a single cap and what that means.

MPM

[DonMoose]

I think the only point in using two larger caps in series is so that a lower voltage rating can be used, lowering the per part cost, at the expense of more parts. I've wondered about the ESR of the two caps in series, paralleled with the balancing resistors against the ESR of a single cap and what that means. MPM

That's the right reasoning about the series caps.

On the ESR question, at audio frequencies and the relatively modest currents we're talking about, the higher ESR means pretty precisely dick. You worry more about ESR for high-frequency, high-current-slew-rate applications like CPU power supplies.

... just my stupid opinion, of course.

[BobW]

martin manning wrote:
I think the only point in using two larger caps in series is so that a lower voltage rating can be used, lowering the per part cost, at the expense of more parts. I've wondered about the ESR of the two caps in series, paralleled with the balancing resistors against the ESR of a single cap and what that means. MPM


That's the right reasoning about the series caps.

On the ESR question, at audio frequencies and the relatively modest currents we're talking about, the higher ESR means pretty precisely dick. You worry more about ESR for high-frequency, high-current-slew-rate applications like CPU power supplies.

I agree, ESR and ESL is usually measured at 100 kHz, but in the case of paralleling say a ceramic and an electrolytic, you won't get a true parallel value. Since the caps are not ideal, you still get a steering of lower frequencies through the electrolytic, and higher frequencies through the ceramic. You still have essentially the same electrolytic cap value at the lows, and the ceramic value at the highs. To obtain a true parallel or series vaule, it's best to use the same cap types be it polys, ceramic, tantalums, plastic (mylar), electrolytics, etc.

[ayan]

2. Two 47uF in series gives you 94uF

Gil

Here's the real typo

Too many typos! Time to retire, goodbye! (Well, you wish!)

Gil

[soje]

I might be trying to learn everything at once. Time to lay off of the coffee

I guess my questions can boil down to this:

Disregarding price, is there any reason to use 2 caps in series, instead of just 1 cap?

Somehow Dumble amps doesn't strike me as budget amps, so I wonder why he used the "precision PSU" with more components.


Am I making sense?


Regards
soje

[Bob-I]

Disregarding price, is there any reason to use 2 caps in series, instead of just 1 cap?

To double the voltage is can handle.

[Structo]

Interesting also is the use of balancing resistors in Dumble supplies.
Sometimes called equalizing resistors.
This is done to control the voltage sharing across each cap in series and makes the voltage equal on both. It also helps counter leakage of the caps.

As a side benefit, they also function as bleeder resistors, discharging the caps at shutdown.