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Please confirm 150W offline PSU is trash?

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Advanced Member level 5
Jun 13, 2021
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Please confirm that this 150W offline SMPS is trash?...
So, Our customer had an offline PSU designed for them and asked us to test it to check it.

Their supplier has already tested it and says its fine.
Spec is ……..
100-265VAC input.
Pout = 150W, but withstand 230W for 20 seconds at a time.
Vout = 37V

It has approx. 5vpkpk 100Hz ripple when at 150W and 115VAC…so I am guessing it’s a single stage Flyback PFC. Its very small, only some 70cm by 35cm by 60cm, enclosure is totally sealed plastic.

Their supplier claims efficiency of 90% at 110VAC, right through from 25W to 150W……we say that’s gotta be utter nonsense, would you agree?
Their supplier claims efficiency of 90-92.5% at 230VAC, right through from 25W to 150W…again we say that’s utter nonsense….do you agree?

Input current instability
…From 100VAC to 240VAC the mains input current is festooned with a 1kHz oscillation as attached. They say that that only occurs when its run through an isolation transformer……..we say that just means they have messed up the input filter and PFC feedback loop…would you agree?

….Above 240VAC, the mains input current has a 50% dead time!!!...(as attached)….we say this is diabolical for a PFC stage…would you agree?

Load transient:
It immediately drops out to 0V when an 8R19 (167W) load is switched in as a step load….stays at 0V for 2 seconds then recovers…..we say this is very very poor…would you agree?
Their supplier test spec claims power factor of 0.47 to 0.74 at 230VAC from 15W to 150W...we say thats diabolical...would you agree?

Isolation transformer used:


In short would you agree with us, that this PSU is trach, and is simply not worth any further testing?


  • PFC vout and IAC_input _150W 115VAC.jpg
    PFC vout and IAC_input _150W 115VAC.jpg
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  • PFC vout and IAC_input _240VAC 150W.jpg
    PFC vout and IAC_input _240VAC 150W.jpg
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i don't think 70 cm by 35 cm by 60 cm is small
maybe you should just test it to see if it meets the spec.
sorry i meant 70mm by 35mm by 60mm.
--- Updated ---

....woops, i kept forgetting i had the isol transformer there, as before always used variable AC source or raw mains. At 240VAC it doesnt ring with the isolation transformer any more, and the dead time there is 50%.
The Resonant frequendcy of the leakage L (read "Line inductance") and the upstream cap of the SMPS should be < 100Hz it seems.
--- Updated ---

The mains point was that at 240vac+, it no longer oscilaltes with the variac/isoal transformer leakage, but dead time is 50%.
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