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LM5041: EVAL board Feedback

Nesh Johny
Expert 1310 points
Part Number: LM5041
Other Parts Discussed in Thread: TL431, TLV431, TLV341

Dear Sir,

I wanted to understand the practical advantage of using Capacitor C42 (22nF) from output live to feedback optocoupler.

Also if I configure my output to 3.3V/30A , then in the feedback section TL431 with 2.5V reference or TLV431 with 1.24V reference which will give better regulation and good for a power supply. 

A smaller reference or higher reference which will be better for the feedback section.

Thanks & Regards,

Nesh

  • 0
    TI__Mastermind 31580 points

    Hi Nesh,

    The capacitor increases the high frequency gain of the control loop by providing a low impedance path for high frequency signals around R12.

    I would use the TLV341 with a 1.24V reference. The TL431 is a 2.5V reference and when used with a 3.3V output it leaves very little voltage to drive current through the forward Vf of opto-coupler diode.

    Regards

    Peter

  • 0 in reply to Peter Meaney
    Expert 1310 points

    Thanks for the reply sir.

    If I bias the opto-coupler diode with a separate 12V secondary supply  as shown in attachment then we use 2.5V TL431 for feedback of a 3.3V output?

  • 0 in reply to Nesh Johny
    TI__Mastermind 31580 points
    Hi Nesh,

    You can use the TL431 if you bias it from the 12V rail, however the transient response will be better if the TL431 device is biased from the actual output voltage that it is regulating.

    In the event of a load transient event there is an instantaneous change in the output voltage which is fed through the opto-diode before the TL431 has time to respond. This effect speeds up the response of the voltage regulation loop.

    Regards

    Peter
  • 0 in reply to Peter Meaney
    Expert 1310 points
    thanks a lot sir, for the immediate response.