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UCC2889: Issues with line voltage detection and long on times

Genius 9310 points

Replies: 4

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Part Number: UCC2889

Hi team,

Posting for a colleague:

Currently working on a bias supply using the UCC2889 controller running from 600-1200Vdc. I’ve run into some issues regarding the Line Voltage Detection and unexpectedly long on times.

 

The supply as currently designed was expected to have a maximum line voltage fault threshold of 545V, with a typical threshold of 436V.  The part appears to be staying in the line voltage detection fault state until nearly 600V.  Ron is 1.8Meg.

 

The supply also has longer than expected on times.  Measured on time is 4.36µs at 600V and 2.61µs at 1200V.  Expected on times are 3.77µs and 1.878µs.  Ron is 1.8Meg, Ct is a 270pF NP0 ceramic, Rs is 1Meg.

Any idea what could be causing this?

Thanks,

Nate

4 Replies

  • Nate,
    Thanks for the interest here. I hope you're well.

    I will have an apps engineer on my team take a look at this. You should see a response tomorrow.

    Can you include some more information?: What is the output voltage, output current, and topology? Do you have a schematic or waveforms you could share?

    Regards,
    John
  • In reply to John Stevens:

    John,
    I'm the engineer who originally passed the questions along to Nate. The output voltage is 25V. Output current is 300mA total from two separate 150mA outputs. The topology is a cascaded flyback, with a coupled inductor at the output to provide two isolated outputs. I'll send the schematic to Nate so he can share it with you.
    -Jay
  • In reply to Jay Goodell:

    I was able to spend some more time in the lab today with the supply. Not surprisingly, the supply under voltage thresholds appear to be much more inline with expectations when the start up circuitry is bypassed (D3 and Q2 removed), and the Ron current is brought directly to the Ton pin. I'll investigate more tomorrow.
  • In reply to Jay Goodell:

    Hi Jay,
    From the schematic , there are many bypass circuit connected to your 1.8M Ron which will affect current of I(Ton). You are right to consider the effect of startup circuit.
    I think Both of your problems are related to this.

    Br

    Kening

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