Re: Switching power supplies

Glenn Little

My take on this after replacing thousands of surface mount electrolytic capacitors is replace them all when you get a new to you device that is more than ten or so years old.

Switchers are harder on electrolytics because they run at a higher frequency than a linear supply and the bean counters usually required the least expensive part to be installed to get the instrument out of warranty.

My take on surface mounted electrolytics is that the fail for two reasons. The seal where the positive lead exits the case was violated during the reflow process. Or the capacitors was not properly selected for the task at hand.

When I replace power supply capacitors in switchers, I select the highest temperature capacitors available with the highest ripple current rating that will fit into the available space. I do not use 85 degree C capacitors unless they are all that is made in that value and voltage.

When doing repair work on cameras and tape decks in TV stations, I never saw a failure of a capacitor that I replaced with the above guidelines. I may have not waited long enough or may have been lucky.

Large computer grade electrolytics are the exception. Do not replace unless needed. These do not usually cause board damage that cannot be repaired.


Hope this helps.


On 3/26/2019 4:37 PM, Brendan via Groups.Io wrote:
I have a few questions about power supplies and would like some opinions. Are switching powers supplies inherently harder on components than linear power supplies? If you picked up a 70's-80's vintage scope with a SMPS would you replace power supply components before using it as a daily driver? Or do you treat all power supplies the same and visually inspect, check for ripple and call it good? From my reading it seems that when a SMPS melts down the chain reaction damage has the possibility of being bad.


Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"

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