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Open Loop TPS40210 Design

Daniel Martin
Prodigy 20 points
Other Parts Discussed in Thread: TPS40210, TPS40210-HT, UC3844

Hello,

I was hoping to get some support on an open loop PWM circuit using the TPS40210. The idea would be to use the IC to generate a fixed frequency, fixed duty cycle to feed a  an unregulated flyback converter. It pretty much needs to utilize the TPS40210-HT because of its operation in 200C ambient conditions. Any help would be appreciated.

Thanks,

Dan

  • 0
    TI__Mastermind 35205 points

    Hi Dan,

    Theoretically this should work. You would need to apply a fixed voltage to the COMP pin to set your fixed duty cycle. I've never done so myself but I will find out if anyone has done it before as an example. I expect you would also see your duty cycle vary from part to part based on the gain of the current sense amplifier (ACS).

    Regards,
    Anthony

  • 0 in reply to Anthony F
    TI__Mastermind 35205 points

    Dan,

    After some more thought using the TPS40210 might not be the easiest way to design an open loop flyback. I was thinking incorrectly originally because in current mode control the COMP pin voltage corresponds to a peak current value and not a duty cycle. This peak current value corresponds to an input power which must be delivered to your output. I think this can only work if your load is on all the time.

    You may want to consider a part such as the UC3844 to design this. It has a max duty cycle of 50% that I think can fixed by grounding the FB pin. I have not personally designed with this part before.

    Can you describe more of your applications conditions and needs which led to this design? Such as input and output requirements.

    *EDIT* Ah forgot about your 200 deg C requirement.

    Regards,
    Anthony

  • 0 in reply to Anthony F
    Prodigy 20 points

    Thank you for the time Anthony, yeah I have the 200c requirements. I'm mainly using the TPS40210 due to its ability to drive a power device. I can easily create a 555 circuit to produce a fixed frequency fixed duty cycle, but it has an open collector output and low current drive capability, and since you guys don't currently make any high temp gate drivers, I came to the idea of an open loop TPS40210. Any other ideas?

    Thanks,

    Dan

  • 0 in reply to Daniel Martin
    Prodigy 80 points

    I have almost the same issue as above and am considering the same solution.  Is there a better solution, or were you able to run in open loop with the TPS40210?

    -Ed