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UC1825: Opel loop operation of UC1825

Nandha Kumar5
Intellectual 470 points
Part Number: UC1825

Hi, I am currently using the UC1825 in open loop mode. And I see the following waveform in at the output of the error amplifier (where the output is expected to be DC). Is there a possible explanation for this operation

Thanks

  • 0
    TI__Mastermind 25570 points

    Hello Nandha

    Please check the INV and NI inputs to the error amplifier. If I wanted to run this device open loop I would ground the INV input and tie the NI input to VREF. If this doesn't solve your issue then please post your schematic here -

    I hope this helps

    Regards

    Colin

  • 0 in reply to Colin Gillmor
    Intellectual 470 points

    Hi Colin,

    Grounding the INV input to ground would drive the IC to its full duty cycle limit (the voltages are fine in this config). I want to control the duty cycle of the output using a 10k pot. Doing so led to this result. Any other way to control the duty cycle in open loop

    Thanks and regards

    Nandha

  • 0 in reply to Nandha Kumar5
    TI__Mastermind 25570 points

    Hello Nandha

    You can configure the on-board error amplifier as a voltage follower by connecting INV to E/A OUT and putting a DC voltage on the NI pin. The DC voltage will control the duty cycle linearly once NI is between about 1.25V and 4V.

    A 10k pot from VREF to GND should work nicely.

    Regards