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Must Get Exact Output Voltage?

By on April 24, 2009


In troubleshooting switch mode power supply (SMPS) do we really need to expect exact output voltages at the secondary side? For example, one of the output voltage line should be 15 volt and from the measurement you got only 14.9 or 14.8 volt. So can you accept this voltage result? The answer is Yes definitely because the output voltages from the SMPS have some tolerances too. Another example of the output voltage that is coming out from a voltage regulator 7805  (5 volt output) and you got only 4.98 volt. Can you accept this voltage value? Again the answer Yes unless the output voltage drop to less than 4.95 and etc.The reason i say Yes on both example was because i have came across many SMPS that still performing good even though the output voltages is not the exact value from the manufacturer spec.

For the voltage regulator case and if you have no confident about the output voltage, you can always replace with a good one and see the result.  I suggest that from now on for whatever equipment that comes in for repair (and you have repaired it) take down the output voltages and see for youself what the voltages like and from there you can make your own conclusion. If you never do this and still cannot decide whether a SMPS output voltages is good or bad then you may be wasting your precious time troubleshooting on a good SMPS.



  1. isaac i. sumani.

    January 31, 2012 at 3:26 pm

    here is a repair info. i would like to share to all active members of this site i went through: yesterday i was repairing a decoder, the problem was that when pluged to ac power i found that the led power indicator was blinking, at first i was suspecting of dry joints but it was not after checking for any, i checked and tested all components in primary section and found that ok. then i jumped to secondary section i found that a diode has a very small leakage, i replaced it retest the unit found the same thing blinking, finally i used try and error method that i found that it was a supporting capacitor of 5v that boots microchip processor marked 1000mf 10v and i replaced with 1000mf 16v and the decoder worked again that i did not believe that was it really my handwork, but my wory is on capacitor voltage marking 10v-16v is this oky sir? i need your help please. send me more electronic info. i am proud of your honor sir yong. regards isaac i. sumani, salima-malawi. God bless.

  2. admin

    January 31, 2012 at 8:01 pm

    HI Isaac,

    Yes it is ok to replace a 10v cap with 16 v cap.



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