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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So, are these 431s any good then?
I always thought they were essentially a programmable zener, and I was trained to believe that a zener diode was a crude, noisy form of regulation.
However, a lot of people seem to like them (they feature in the Kwak clock's regulation for instance (admittedly with a driving transistor).
I would of thought a 431 would be better as a first form of regulation, followed by a low noise regulator - but I have no real experience of them (except they worked in my Kwak clock, but no idea how well).
Cheers,
Phil
I always thought they were essentially a programmable zener, and I was trained to believe that a zener diode was a crude, noisy form of regulation.
However, a lot of people seem to like them (they feature in the Kwak clock's regulation for instance (admittedly with a driving transistor).
I would of thought a 431 would be better as a first form of regulation, followed by a low noise regulator - but I have no real experience of them (except they worked in my Kwak clock, but no idea how well).
Cheers,
Phil
philpoole said:
They are nice but not quiet, the equivalent noise at the ref input is 100nV/SqrrtHz and the LF noise increases rapidly.
LEDs are quiet but more temperature dependant. That usually doesn't matter that much as most components are quite tolerant in terms of absolute supply voltage.
best
Guido
philpoole said:
the combo of a 431 and 317 as shown in the circuit forms a shunt regulator. This type has some advantages over traditionally used series regs. The point however is that the shunt element defines the noise here.
A 317 isn't that quiet either, look at the noise specs in the datasheets.
An interesting thread about noise has beeninititated by Critter, also on DIYaudio
best
Hi Guido, Nigel,
Thanks for the replies. It makes sense now that it is used for its more stable voltage, rather than its noise.
I agree that the 317 is not particularly low noise (hence I suggested why not just use that instead, as I couldn't, at the time, see an advantage for the 431).
So, a 431 is good for a DAC, as intermediate output values are generated from it (if, that is, the power rails are used as reference voltage on the TDA1541A {I know it doesn't have a seperate Vref input like other DACs}), but a 431 may not be as important for, say a preamp, or a clock module, as we're more interested in having low noise and enough headroom.
Hopefully, I'm starting to understand.
Thanks again.
Phil
Thanks for the replies. It makes sense now that it is used for its more stable voltage, rather than its noise.
I agree that the 317 is not particularly low noise (hence I suggested why not just use that instead, as I couldn't, at the time, see an advantage for the 431).
So, a 431 is good for a DAC, as intermediate output values are generated from it (if, that is, the power rails are used as reference voltage on the TDA1541A {I know it doesn't have a seperate Vref input like other DACs}), but a 431 may not be as important for, say a preamp, or a clock module, as we're more interested in having low noise and enough headroom.
Hopefully, I'm starting to understand.
Thanks again.
Phil
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