not sure how accurate, but i in the past have used a band gap reference
diode and a jfet as a constant current regulator..... use it ... dont use
it.
We used them as references for power supplies and voltage meters.

J
----- Original Message -----
From: "Bob Axtell" <cr_axtell@YAHOO.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, July 31, 2003 9:09 AM
Subject: Re: [EE]: zener voltage regulator design


> That's a pretty classic linear regulator design using a transistor and
> zener. But there are problems with it:
>
> 1. Zeners tend to be "soft" at the regulation point. To maintain a
constant
> regulated voltage, the currect has to be high enough to make SURE the
> voltage remains above the "regulation knee". With a 9V input, I don't
think
> any zener will stay above the knee with a 12K resistor.
>
> 2. The ability of the transistor to absorb the heat generated is the
> question. Thats the reason someone said 100mA.  The transistor will have
to
> dissipate (remove into the surrounding air or PCB) the difference between
> 9V and 3V (6V) so at 100mA that means (P=I*V) a wattage of 0.6W. Can the
> transistor do that?
>
> A better way to do it is with commercial voltage regulators. Everything is
> trimmed and tested and most will hold your 3V at 5% or better accuracy.
> Costs $0.25 USD, best bargain in town.
>
> --Bob
>
>
> At 03:08 PM 7/30/2003 -0500, you wrote:
>
> >I need a design for regulating 9V down to around 3V with a zener
(simple -
> >no bells and whistles).  the current capacity must be up to about 100ma.
> >attached is a schematic of my design (the parts may not be ideal - but I
> >designed with what I had).  My question is: will this design work for
what I
> >need? I wanted to use just a zener and a resistor but I've read that this
> >design will only supply up to 50ma (this might be ok but better safe that
> >sorry).  thanks for checking - I've never designed with a zener before.
> >
> >-Clayton
> >
> >
> >--
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> >mailto:piclist-unsubscribe-request@mitvma.mit.edu
> >
> >
>
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