Dirty output switching mode power supply

Question I have problems with a switching mode powersupply with multiple different voltage outputs like a computer PSU.
How can I get the output as clean as possible? that is very important for me.
I have a couple of options I think normally it uses a very small form factor 10.000uf capacitor at the 5v among with some other values for the other outputs.

1. using something like 10 2200uf low esr electrolytic capacitors in parallel, instead or amongst the 10.000uf cap.
2. buying a reel with 100x 330uf tantals and put something like 40 in parallel.
3. both using a couple of low esr electrolytics and tantals or a lot 22uf ceramics.
4. something else any idea?

You may use an external PI LC Filter added to the power supply outputs.
Choose an inductor with a current rating double to the maximum output current of the power supply.
A large value of inductor will require a large value of capacitor and the response of the filter will be slowed, so for a compromise it is recommended to choose a small value inductor, typical value 1-10 μH.

Dear nixiepixie
Hi
What topology ? did you design it with yourself or just bout it ?
and about frequency of operation ?
Regards
Goldsmith

No it is a stock power supply in a nearly 20 year old vector network analyzer.
I have to measure what noise is coming out, it is a long time ago I did measure that!
Tomorrow I can not do that, becouse I am away.
But I think it will mostely be the switching frequency of the supply that is maybe 40khz but I have to measure that.
In the old days they made a lot use of choke coils but they where primary for 50hz so I have to make my own.

you can use a simple differential LC filter .
But if you try to design your own , you won't have these problems.
Best Wishes
Goldsmith

so by adding a inductor before the capacitor I can make a better filtering then alone a capacitor? Never thought at that! very nice
And how about a high pass to ground?

Do you know that what i mean by , differential filter ? ( two coil in one core , and in series with gnd and main line )

Hi you mean like this?
**broken link removed**
Isn't that a mains filter for alternating currents?
I have dc out of a switching power supply. Having problems with noise.
I do not know if I can call the output floating, mybe if the psu does not have a connection betweet to the case, the negative is common like a computer psu.

I want to build this charger do you know why there is a transistor used as some kind of diode?
The designer claims it is to get is oscillate but is that true? the capacitor and zener will take care of the oscillation right?
Why not a diode in place of the transistor?

see:
CIRCUIT2

It is a charger that will charge and trickle charge a alkaline or other batteries with a switchabale potmeter/resistor 47R...
He did not mention rechagable alkalines or regular but I am not feint hearted and wil not use them in long storage devices only in remote controls or what so ever.

Again Hi
The cores are on one core , and at resonant frequency , the core will get differential of same harmonics ( v-v) . thus the DC voltage has permission to go through it but the AC not allowed.
Regards
Goldsmith

You can’t use this differential filters in a power supply with multiple outputs, we need to keep the ground bus clear, no ground loops in the circuit follow the ideal single point ground concept, that will insure no ground loops are created. Use simple filters with series inductors for each output and capacitors to the ground. Use multilayer ceramic capacitors in parallel for each electrolytic capacitor to reduce low equivalent series resistance (ESR).

"Isn't that a mains filter for alternating currents?"
Yes they are but they prevent noise and power drill spark that are high freq to go back into the mains . check your switching freq to design your rc or rcl filter and use scottky diodes and mov's .
use scope to see if its high freq ripple or spikes larger that output

my mean wasn't that clearly . something like that , with a simple capacitor and two inductor on one core . that i used for some of my power supplies and class D and E amplifiers .
Regards
Goldsmith

It is usable for dc I see on this page also, I do not understand why the filter in the power supply is not sufficient?
see page in dutch Zelfbouw Filter voor de IC706

A easy and cheap filter will do the job and the company that builds the power supply especially from a network analyzer is not good! I can not understand it.
Maybe I have to replace every capacitor inside also the 250v ones.