Switching Mode PSU
Switching Mode PSU
(OP)
Hi,
I am trouble shooting on a switching mode psu.The fault is high ripples when connected to a load.It is providing 13.5Vdc/5A output...I have change all the capacitors on the unit and still the ripples are high about 2volts p-p riding on the dc line...Any suggestion
I am trouble shooting on a switching mode psu.The fault is high ripples when connected to a load.It is providing 13.5Vdc/5A output...I have change all the capacitors on the unit and still the ripples are high about 2volts p-p riding on the dc line...Any suggestion





RE: Switching Mode PSU
You mean:
Or 0.2V?
or 0.02V?
or 0.002V?
How are you measuring this?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Switching Mode PSU
RE: Switching Mode PSU
Hi Keith,
It is 2volts peak to peak (Spikes)...I used a oscillscope to measure.
Rgds
Kochcha
RE: Switching Mode PSU
This was THE problem in the first place? The ripple?
And you replaced the caps and IT CHANGED NOTHING?
There are several possibilities. If you would tell us a LOT more we could probably be more helpful.
Switchers must have ripple in their outputs or they cannot properly control the cycle to cycle wave forms correctly. Of course large ripple is wrong too. You could get large ripple if the switcher was running at way too low a frequency. Or if the sense resistor that controls the current limit has changed value.
Can you hook it to a much smaller load and see what happens? Can your load be wrong or faulty and be sinking too much current?
If the caps are ultra low ESR caps and one failed open this could greatly increase the ripple. If you then replaced the all the low ESR caps with standard caps you would have the same problem again. You might need 5 times as many regular caps to get the ESR down to the design value.
What frequency is your ripple?
What frequency is your switcher supposed to be using?
What is the current your load is ACTUALLY drawing as measured with a TRUE RMS reading voltmeter?
What is the measured output voltage?
Can the supply be run with no load? (Some switchers CANNOT take this.) If your's can, what happens when you run with the load disconnected?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Switching Mode PSU
RE: Switching Mode PSU
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Switching Mode PSU
What frequency is your ripple? 50Hz
What frequency is your switcher supposed to be using? 50Hz
What is the current your load is ACTUALLY drawing as measured with a TRUE RMS reading voltmeter?...5Amps.
What is the measured output voltage...13.5Vdc
Rgds
Kochcha
RE: Switching Mode PSU
All switchers use much much higher frequencies then your line frequency. That is the fundamental basis of their existence. If they didn't, they'd be 10 times more expensive and the size of bread boxes.
So for you to tell us that the ripple frequency IS your line frequency, means you are measuring something related to your line power or grounding or 'scope clip placement' or a bad line filter or line filter ground. It's not your switcher having a problem.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Switching Mode PSU
RE: Switching Mode PSU