Mail Archives: geda-user/2020/12/15/00:22:01
Den 2020-12-15 kl. 02:24, skrev gene glick (geneglick AT optonline DOT net)
[via geda-user AT delorie DOT com]:
> 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.
It's used for switched power electronics so noise is not important.
>
> 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.
It's good to know about the noise problem even though not important this
time, missed that, guess maybe LDO may amplify noise. I found zener
diodes are rather good tolerating high temperature but do not remember
about accuracy.
>
> 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.
Adjustable have but most are fixed LDO and they do not show resistor
divider to get variable voltage. It is possible to get variable voltage
from the fixed even though datasheet does not show by using resistor
network but ground current add a bias and low resistor value add some
power loss, zener diode add some accuracy error.
TL431 have no loss problem and good enough accuracy with margin so using
this with resistor network on fixed LDO would be a good choice. Only
thing that worries me is I happen to come close to instability as I read
LDOs may have this problem and then produced in larger numbers it will
come back bite my ass.
>
> For low power, it's hard to beat SOT23 TL431 + SOT23 2N2222 + a couple
> resistors. Very small, very flexible.
Power is lower but space is a little bit limited, plenty of space at
other places of the board but not there needed.
>
> Hope that helps.
Yes it does, it' always good to ask people with more experience.
Regards Nicklas Karlsson
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