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Original question:

TL2845: Error Amplifier Output source current

TL2845: Combined with optocoupler

Masakazu Adachi
Intellectual 2500 points
Part Number: TL2845
Other Parts Discussed in Thread: TL431

Hello team,

Regarding this tread: Error Amplifier Output source current

If optocouplers are used as discussed in the above thread, how should the pull-up resistor value be determined? Could you please explain that how to calculate the maximum and minimum values?

Regards,

Masa

  • 0
    TI__Mastermind 29055 points

    Masa

    The E2E thread you referenced is asking how to set up the collector side based on 0.5mA available from the COMP which is feeding the diode side of the optocoupler - is this the same as your proposed use case? It sounds like you want to transfer the DC voltage equivalent of the COMP signal across an isolation barrier using an optocoupler? Is this correct and if yes, is the secondary side referenced to another ground or are you proposing a level shift? Can you please provide a detailed schematic drawing so I can better understand what you are trying to accomplish?

    Regards,

    Steve M

  • 0 in reply to Steven Mappus1
    TI__Intellectual 2500 points

    Hello Steven,

    I added the additional information. This is the circuit configuration of another company, and the customer wants it to be like this. Is there any further information you would like to provide to further the discussion? 

    Regards,

    Masa

  • +1 in reply to Masakazu Adachi
    TI__Mastermind 29055 points

    Masa,

    The schematic you've shown is different compared to what I though you were originally asking. Thanks for the clarification! The schematic you are showing demonstrates TL431 + optocoupler feedback for a flyback converter. This is a fairly popular and mainstream technique for feedback control loop design of a flyback as well as many other isolated converter topologies. SLVAF37 and SLUAA66 are two TI design resources you can consider or you can search the web for something like "TL341 optocoupler feedback flyback"

    Regards,

    Steve M

  • 0 in reply to Steven Mappus1
    TI__Intellectual 2500 points

    Hello Steve,

    Thanks to suggest it.

    Regards,

    Masa