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Re: gEDA-user: TL431
-> Anyone use these shunt regulators? I'm wondering about the max voltage.
> Data sheet says max cathode-to-anode voltage is 36V. What if VCC = 50
> V, as in this cheezy drawing is trying to show. R1 and R2 set the
> output voltage at the emitter. R3 limits the current to the cathode
> *and* drops enough voltage (greater than 14V) to allow the the
> cathode-anode voltage to be within 36V. Is that legit? Or maybe I have
> to design in some circuitry to drop the voltage down at the cathode.
>
> (npn)
>
> VCC ------ C E ------
> | \ / |
> / ----- /
> R3 \ | B \
> / | / R1
> | | \
> --------| /
> | |
> | |
> ------/ |
> / / \ |
> TL431 / \---------
> ----- |
> | /
> | \ R2
> | /
> | |
> | |
> ------------
> |
> --------
> / / /
>
It is nothing wrong for TLC431 if the supply voltage is greather than 36V, providing the R3 limits the current to safe value. Both maximum current for TLC431 and its power dissipation have to be checked for maximum input voltage. The maximum voltage for TLC431 limits the maximum output voltage, which is 36V minus VBE voltage of the transistor.
Wojciech Kazubski
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