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Original question:

UCC28019: PFC Circuit PFC Circuit Unidentified Error

UCC28019A: Maxed output of the IC

SJZ
Prodigy 185 points
Part Number: UCC28019A
Other Parts Discussed in Thread: UCC28019

Hello,

In the thread I referenced, the gate waveforms from the IC, on time is coming out to be maxed out.

As per the explanation mentioned in the thread: 

"If you notice, your COMP voltage is maxed out (in fact, it is exceeding the 7V AbsMax spec!). Your gate on-time is maxed out and VSENSE is on the high end. The PFC has likely hit it's OCP level and you are peak-regulating (√2 * 230Vac + Vdiode = 326V)."

What might be causing the Vcomp to exceed and thus leading the gate on time to be maxed out here? 

Also, what does "Vsense(4.1V) is on the high end" mean when its typically referenced value is for 5V?

Regards,

  • 0
    TI__Genius 14210 points

    Hi,

    Can you please post reference to the thread here?

    Regards,

    Harish

  • +1 in reply to SJZ
    TI__Genius 14210 points

    Hi,

    Vcomp can reach absolute max value especially during startup and load transients where control loop could demand a higher current.The UCC28019 has an extra internal source current feature (typically about 150uA but this varies with different conditions) that becomes enabled when soft start is finished (when Vout reaches 95% of its nominal design point).  This extra source current is the EDR (Enhanced Dynamic Response).  This extra EDR goes through the VCOMP resistor to add voltage to the VCOMP level, driving VCOMP immediately high.I am not sure on the VSENSE comment and I feel it is ok for the 326V obtained. Please post the schematic or share the excel calculator for any questions related to your design.

    Regards,

    Harish