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Synchronise the soft start of two UC3823

Francarl Galea
Prodigy 20 points
Other Parts Discussed in Thread: UC3823

I have two Cuk converters controlled by UC3823 and in order to connect them together, I have to figure a way how they can start together. Is there a way to synchronise two UC3823 PWM controllers so that they soft start exactly at the same time. I tried to short their SS pins but first one of them starts independently, then it stops and after a short pause both start together.

  • 0
    TI__Guru 60555 points

    You are trying to do soft start sychronization dynamically. There is usually not an easy way to do so. Why do you want to get this would be first considered as some additional circuit would have to be added. If you would like to share the load current during the start, I would suggest adding a load sharing cirucit instead of doing soft start synchronization.

  • 0 in reply to Hong Huang
    Prodigy 20 points

    The inputs of the two converters are connected in series. By shorting their SS pin, one soft starts indipendently, then it trips and then they start up together.  I do not know what is happening.

  • 0 in reply to Francarl Galea
    TI__Guru 60555 points

    I think you need to check each IC start up condition to see if the start up condition present at the same time. As the two converter's inputs are in series, I think their input voltages are not necessarily divided even. Check and find out if the start up conditions occur at the same time - which is usually difficult to have. Also each IC parameters may show some distributions which may also be part of the reasons.