[sdiy] zener question

[patchell]

    Yes, run a resistor from the 12 volts to the Zener.  The size of the
resistor will depend on the size of the load.  A zener shunt regulator
is generally useful onl when the load is known for reasons which will
become apparent in the next sentence.  To calculate the size of the
resistor, find out what the load current is and what the zerer bias
current is.  If you don't know the zener bias current is, you might have
to experiment a bit.  For example, if the zener bias is 10mA and your
load is 90mA, the resistor will be R=(12-9)/100mA or 30 ohms.  Now, if
for some reason your load current goes away, the zener will be taking
the full 100mA which means it will be disapating 900mW, which will
probably make it very hot.

    If the voltage you are trying to create is for a voltage reference
type app (very low current), just use a resistor that will bias the
zener at its bias current.


Ken MacBeth wrote:

> Hi! I'm wanting to convert -+12V into -+9V using zener
> doides, how do I do this, and do I use resistors as
> well?
> Thanks in advance, Ken....
>
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--
 -Jim
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