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UCC28060: instability issue with 115Vac input

P de Winter
Prodigy 40 points
Part Number: UCC28060

Hi all,

I made a design with the interleaf controller and everything is working very good except with a input around 115Vac.

The load on the PFC is around 600W when it happens.

If I put 115Vac on the input and I measure on the output of the PFC I see that the output starts climbing up and than the gates stop switching.

The green line is the gate of B the gate of A is acting the same.

The yellow line is the Vin_ac 

The blue line is the output of the PFC.

What I think that is happening is that for some reason the output climbs up to the OV level of the Vsense than the controller switch off the gates and restarts and than it happens again.

If I toggle the load on the output than it get into a stable signal without climbing.  

If I put 90Vac or 230Vac on it everything works great but around 115Vac the issue is back.

My question is has anybody any idea what is happening and how to avoid this?

Why jumps the Vin_ac up?

Why is this not happing with a input of 90Vac and 230Vac?

Any help is welcome.

Thanks Patrick

  • 0
    TI__Genius 11350 points

    Hi Patrick,

    At around 3.5V on VINAC the IC jumps between low-line and high-line settings. There is a sub-harmonic oscillation caused by the sudden on-time change at this threshold and the response of Vcomp. This difference can result in the output hitting OVP. A solution to this is to feed the input voltage before the bridge directly into VINAC (with individual blocking diodes). Here is an example:

    Give this a try and see if it resolves the issue.

    Ray