PFC'd SMPS that resonates with isolation transformer leakage.

[Flyback]

Hi,
Please confirm that this 150W offline SMPS is poor?...
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
Isolated

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 70mm by 35mm by 60mm, enclosure is totally sealed plastic.

Efficiency
Their supplier claims efficiency of 90% at 110VAC, right through from 25W to 150W……we say that’s gotta be a little off, would you agree?
Their supplier claims efficiency of 90-92.5% at 230VAC, right through from 25W to 150W…again we say that’s off….do you agree?
Input current instability
…From 100VAC to 240VAC the mains input current is festooned with a 1kHz oscillation as attached. That only occurs when its run through an isolation transformer……..
….Above 240VAC, the mains input current has a 50% dead time...(as attached)….we say this is poor 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 poor…would you agree? This also happens also at >240vac when it no longer rings with the isolation transformer.
PFC
Their supplier test spec claims power factor of 0.47 to 0.74 at 230VAC from 15W to 150W...we say thats poor...would you agree?

Isolation transformer used:

Carroll & Meynell 3000VA Intermittent Isolation Transformer 230V/230V Blue - Screwfix

Order online at Screwfix.com. Rugged portable isolating transformer, designed to ensure an isolated supply when working on equipment connected to the mains supply. With a resettable thermal cut-out in the primary circuit to prevent overload. Glass-reinforced polymer case provides IP44 ingress...

www.screwfix.com

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[For The Popcorn]

Maybe you should just refer your client here. He can get a consensus vote without (paying) the middleman.

Do you have any efficiency measurements across the range? Or do you just think it can't be true?

 

[Papabravo]

I would tread very very carefully here. Have your lawyer advise you on your legal risk for getting involved in this. You could lose your company regardless of whether you are right or wrong. Tell them you are happy to give them a quote on a replacement with better performance, but don't get in the middle of this one unless you have good insurance and they sign off on this activity.

 

[Flyback]

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