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TL783: using for voltages above 125 V

John Woodgate
Prodigy 140 points
Part Number: TL783

Is there a better way of using TL783 above 125 V output than simply setting a single device to produce 200 V out and protecting it with three 39 V zener diodes?

  • 0
    TI__Mastermind 43630 points

    Hi John,

    The datasheet has an absolute max delta Vin-Vout of 125V.  While not explicitly stated, this should apply from Vout to ADJ. 

    If Vin can always be slowly ramped such that these abs max ratings are not violated it is conceivable to use a Zener diode in the ADJ pin to float the regulator. What I mean by slowly ramped is that if a voltage greater than 125V is hot-plugged onto the device, until Vout can ramp up, then abs max rating of the device will be violated. 

    To answer your question, No. I do not see a better way other than what you propose.

    I hope this answers your question.

    Regards,

  • 0 in reply to JCHK
    Prodigy 140 points

    I can't ramp up the input voltage. Can I 'stack' two TL783 circuits across a 250 V supply, with the output voltage controlled by a 2-gang pot, and three 39 V Zeners across each TL783 for protection? I only need tens of mA output.

  • 0 in reply to John Woodgate
    TI__Mastermind 43630 points

    Hi John,

    That might work. We don't have an official model for the TL783 (But there is an unofficial one here https://e2e.ti.com/support/power-management/f/196/t/197768 ) so I am not sure simulating this would accurately show what happens when the input voltage is applied. 

    The key is to make sure that absolute maximum ratings of the device are not violated. Since your load current is so small, it might be a good idea to add an input resistance in series with VIN and a Zener clamp from VIN to ADJ.

    I hope this can work for you.

    Regards,

  • 0 in reply to JCHK
    Prodigy 140 points

    Thank you. I am a bit puzzled about putting a Zener from Vin to ADJ. That would be a low-current 125 V Zener? If it conducts, the ADJ voltage rises, so the Vo rises, reducing the voltage from Vin to Vo. Also, the Vin falls, because of the series resistor. Is that how it works? It seems better than connecting a 125 V Zener from Vin to Vo.  

    Incidentally, I am not getting notifications about your helpful answers.  Are they sent by email to jmw@woodjohn.uk?

  • 0 in reply to John Woodgate
    TI__Mastermind 43630 points

    Hi John,

    Yes using a Zener would raise the ADJ pin voltage while it would impact the output voltage, it might be a way to protect the device itself. Yes, the goal of the series resistor is to help reduce the total drop as seen across the TL783.  It would definitely be worthwhile ordering some free samples and trying it out. 

    I am not sure why you were not getting notifications, but I made sure you are on the notify list for this thread now.

    Regards,