Electronics > Beginners
TL431 linear power supply
<< < (9/32) > >>
mike_mike:
 Thank you for your help.
What about the attached schematic ?
 I already asked on the forum but I still not get a response for some of the questions.
Will it (the power supply) oscillate ?
IanMacdonald:
The main issue with amplified IC regulator arrangements is high volts drop. The LM317 has a rather high burden voltage in itself, and adding a further transistor and series resistor considerably worsens that. Although, it is a workable arrangement if top efficiency is not important.

The gotcha with your TL431 arrangement is that if the volts setting pot develops a bad spot on its track, the load is going to have its magic smoke forcibly removed, because the output will go straight to max. Putting the pot on the low side of the potential divider eliminates this risk, at the expense of the control being rather nonlinear. If it's a one-time preset that doesn't matter too much though.

To achieve proportional control of voltage whilst being 'o/c wiper safe' generally requires a noninverting opamp arrangement fed from the pot's wiper, as in spec's reply.
David Hess:

--- Quote from: not1xor1 on December 14, 2018, 08:22:22 am ---you must be kidding  ;D
a 20V/µs opamp with a huge 1µF compensation capacitor...
and what would be the advantage versus a proven and foolproof design using the traditional LM723 ?
--- End quote ---

The compensation capacitor is way too large but a fast operational amplifier like that would be selected for lower noise.  I have done the same thing many times using an LT1007 or OP27.
T3sl4co1l:

--- Quote from: spec on December 14, 2018, 08:08:36 am ---I take it then that you yourself or anyone that you know has built a successful TL431 PSU.

--- End quote ---

Good evening spec,

Have you? :)

Tim
mike_mike:

--- Quote from: spec on December 14, 2018, 10:33:23 am ---mike_mike,

Attached is a 723 PSU schematic which I found drifting around my laptop. This, is the kind of thing that not1xor1 and I were discussing.

--- End quote ---
I built this schematic and it works as expected.
The problem is that LM723 will not be available more time from now and I need something that is always available from more than 2 manufacturers.
So this is why I want to use LM317 and pass transistors or TL431.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod