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Subject:	Re: [geda-user] Variable voltage supply from fixed
To:	geda-user AT delorie DOT com
Reply-To:	geda-user AT delorie DOT com

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I've done some of all that. For now, I'll assume you want a positive supply

TL431 is a personal favorite. It works very well as a shunt regulator or
with a transistor to form a higher current series regulator. Both
good...depends on the application.

You did not mention noise or temperature. If noise is important to you,
then you'll need to find a regulator that exposes the voltage reference so
you can filter it. Temperature can affect some of these regulators. I've
run the TL431 to 175C (and higher) with no problems. The band-gap reference
is really very stable. Some regulators have thermal shutdown at 160C.

Zener references are noisy, if that matters for you. If not, zener + pass
transistor is an okay option. I suspect zener's are not thermally stable at
high temperatures.

You can always roll your own with an opamp, a pass transistor, and a
reference. That's pretty much what is inside the TL431 anyway. :D

Also, if you look at the data sheet for any of the 3-pin fixed regulators -
I'm pretty sure they show ways to raise the output with either some
resistors or zener diodes. I haven't tried this, however.

For low power, it's hard to beat SOT23 TL431 + SOT23 2N2222 + a couple
resistors. Very small, very flexible.

Hope that helps.

gene

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<div dir=3D"ltr"><div dir=3D"ltr"><div>I&#39;ve done some of all that. For =
now, I&#39;ll assume you want a positive supply<br></div><div><br></div><di=
v>TL431 is a personal favorite. It works very well as a shunt regulator or =
with a transistor to form a higher current series regulator. Both good...de=
pends on the application.</div><div><br></div><div>You did not mention nois=
e or temperature. If noise is important to you, then you&#39;ll need to fin=
d a regulator that exposes the voltage reference so you can filter it. Temp=
erature can affect some of these regulators. I&#39;ve run the TL431 to 175C=
 (and higher) with no problems. The band-gap reference is really very stabl=
e. Some regulators have thermal shutdown at 160C.<br></div><div>=C2=A0<br><=
/div><div>Zener references are noisy, if that matters for you. If not, zene=
r + pass transistor is an okay option. I suspect zener&#39;s are not therma=
lly stable at high temperatures.<br></div><div><br></div><div>You can alway=
s roll your own with an opamp, a pass transistor, and a reference. That&#39=
;s pretty much what is inside the TL431 anyway. :D</div><div><br></div><div=
>Also, if you look at the data sheet for any of the 3-pin fixed regulators =
- I&#39;m pretty sure they show ways to raise the output with either some r=
esistors or zener diodes. I haven&#39;t tried this, however.<br></div><div>=
<br></div><div>For low power, it&#39;s hard to beat SOT23 TL431 + SOT23 2N2=
222 + a couple resistors. Very small, very flexible.</div><div><br></div><d=
iv>Hope that helps.<br></div></div><div><br></div><div>gene</div></div>

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