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What is the purpose of TL431 in this circuit?
What is the purpose of TL431 in this circuit?
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Old 27th October 2006, 06:01 AM   #1
Sunsun22 is offline Sunsun22  Hong Kong
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Default What is the purpose of TL431 in this circuit?

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?
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Old 27th October 2006, 09:52 AM   #2
Archwn is offline Archwn  United Kingdom
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would be a double regulated config. to increase the performance of the power supply or something. You might get better sound IMHO
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Old 28th October 2006, 03:39 AM   #3
dangus is offline dangus  Canada
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What is the purpose of TL431 in this circuit?
Search for stuff about "shunt regulation". I think that's what is going on here.
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Old 28th October 2006, 09:11 AM   #4
Sunsun22 is offline Sunsun22  Hong Kong
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Yes TL431 is a shunt regulator but is a regulated voltage (from 317 in this circuit) a pre-requisite to perform shunt regulation?
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Old 28th October 2006, 09:48 AM   #5
clem_o is offline clem_o  Philippines
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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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Old 28th October 2006, 01:41 PM   #6
Guido Tent is offline Guido Tent  Netherlands
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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.

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Old 28th October 2006, 02:05 PM   #7
sivan_and is offline sivan_and  India
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TL431 is a band gap referenced shunt requlator..If fed from a constant current source the accuracy will increase..
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Old 28th October 2006, 02:14 PM   #8
Guido Tent is offline Guido Tent  Netherlands
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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 ?

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Old 29th October 2006, 02:02 PM   #9
Sunsun22 is offline Sunsun22  Hong Kong
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I have difficulties to reduce the entire circuit. But with a little help from my friend, here is the complete circuit.
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Old 29th October 2006, 02:12 PM   #10
Guido Tent is offline Guido Tent  Netherlands
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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.

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