What is the purpose of TL431 in this circuit?

Sunsun22 · 27th October 2006, 05:01 AM

This circuit is from a power supply to CS-8412 +5V rail. The DC is 7V from a 317 regulated source. Since this is already regulated by 317 to 7V, we can config 317 to produce 5V. Why does it need to add another regulation stage by TL431? If TL431 is better than 317, then we should feed the DC after rectification and cap to TL431 to produce +5V, then why is it necessary to go through 317?

Archwn · 27th October 2006, 08:52 AM

would be a double regulated config. to increase the performance of the power supply or something. You might get better sound IMHO

dangus · 28th October 2006, 02:39 AM

Search for stuff about "shunt regulation". I think that's what is going on here.

Sunsun22 · 28th October 2006, 08:11 AM

Yes TL431 is a shunt regulator but is a regulated voltage (from 317 in this circuit) a pre-requisite to perform shunt regulation?

clem_o · 28th October 2006, 08:48 AM

Shouldn't be a requirement, but a quieter voltage feeding the TL431 (or any regulator for that matter) should serve to drop the supply noise on that output line further.

Guido Tent · 28th October 2006, 12:41 PM

Quote:

Originally posted by Sunsun22
Yes TL431 is a shunt regulator but is a regulated voltage (from 317 in this circuit) a pre-requisite to perform shunt regulation?

The 431 acting as a shunt should be fed with a current, I suspect the 317 is configured as a current source. Show us the full schematic and it will become clear.

best

sivan_and · 28th October 2006, 01:05 PM

TL431 is a band gap referenced shunt requlator..If fed from a constant current source the accuracy will increase..

Guido Tent · 28th October 2006, 01:14 PM

Quote:

Originally posted by sivan_and
TL431 is a band gap referenced shunt requlator..If fed from a constant current source the accuracy will increase..

Why ?

cheers

Sunsun22 · 29th October 2006, 01:02 PM

I have difficulties to reduce the entire circuit. But with a little help from my friend, here is the complete circuit.

Guido Tent · 29th October 2006, 01:12 PM

Quote:

Originally posted by Sunsun22
I have difficulties to reduce the entire circuit. But with a little help from my friend, here is the complete circuit.

Indeed, the 317's are configured as current sources. Unfortunately the designers short the current sources with lytics - too bad.

best,
-
Guido

28th October 2006, 01:05 PM	#7
sivan_and diyAudio Member Join Date: Dec 2004 Location: Dxb / India	TL431 is a band gap referenced shunt requlator..If fed from a constant current source the accuracy will increase.. __________________ SivanandBalan

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27th October 2006, 08:52 AM	#2
Archwn diyAudio Member Join Date: Oct 2006	would be a double regulated config. to increase the performance of the power supply or something. You might get better sound IMHO

28th October 2006, 02:39 AM	#3
dangus diyAudio Member Join Date: May 2004 Location: Vancouver Island	Search for stuff about "shunt regulation". I think that's what is going on here.

28th October 2006, 08:11 AM	#4
Sunsun22 diyAudio Member Join Date: Jul 2004 Location: Hong Kong	Yes TL431 is a shunt regulator but is a regulated voltage (from 317 in this circuit) a pre-requisite to perform shunt regulation?

28th October 2006, 08:48 AM	#5
clem_o diyAudio Member Join Date: Jun 2005 Location: Manila	Shouldn't be a requirement, but a quieter voltage feeding the TL431 (or any regulator for that matter) should serve to drop the supply noise on that output line further.

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