calcualing the rs resistor for a string of zener diodes

hi

Is there a different equation for calculatling the rs resistor for a string of diodes.


I know how to cal for one..



cheers

skal1

Select the Zener with the largest voltage drop (or any one if they're all the same). Take the Zener wattage and divide it by the breakdown voltage. This will give you the theoretical max current.  Divide this by 10 to get a good working current, Iw.

Figure out the voltage across the series resistor Vr = (Vin - the total voltage of the Zener string).

The resistance will be Vr / Iw.  The wattage needed will be Vr * Iw (times 5 or more for safety).

--mark

Thanks for the explanation mhuss.

just 1 more ? is wise to use more zener's to achieve the voltage you require.

cheers

skal1

I had a tube preamp that used a string of Zeners to generate the HV reference voltage. It worked fine until it failed, then it failed spectacularly.    That said, I would still use a string of Zeners to spread the voltage and power.

--mark