LM317T CCS Improvement

[Audiohifi]

The attached schematic uses LM317 for CCS for a regulator
I understand that it can be improved by replacing it with a resistor
Assuming the voltage is 270V and CCS is 20mA, how to go about it

Audiohifi

 

[AndrewT]

Is this a -ve supply?
Where is the input?
Where is the common?
Is the arrow head the output?

 

[Audiohifi]

Positive supply
arrow is the input
VR goes to the shunt regulator

 

[SY]

The 317 is a mediocre current source especially at high frequencies. For much less money and a lower parts count, you can cascode a pair of depletion mode MOSFETs and get far better results.

 

[jackinnj]

The 317 is a mediocre current source especially at high frequencies. For much less money and a lower parts count, you can cascode a pair of depletion mode MOSFETs and get far better results.

Which you have demonstrated with the Impasse preamplifier, and "His Master's Noise" -- page 10: http://www.diyaudio.com/forums/diya...oughly-modern-tube-phono-preamp.html?garpg=10

Walt Jung wrote up a 2 section article on current sources for AudioXpress and they are archived on his website: Home , in it he discusses the 3-legged regulator and illustrates some performance tests in part II.

 

[abraxalito]

For much less money and a lower parts count, you can cascode a pair of depletion mode MOSFETs and get far better results.

What are you paying for the FETs where you are?

 

[SY]

$1-1.50, depending on quantity.

 

[abraxalito]

Ah, so you're being robbed on the LM317 then.

 

[SY]

50 cents from a distributor who's unlikely to pawn off counterfeits.

 

[abraxalito]

The first price I pulled up for the LM317T (manu ST) is 26.5cents. Can your disty manage 13cents ya reckon?

 

[SY]

Mouser. Never got a fake from them.

 

[Audiohifi]

Noted the CCS using Mosfet in HMN phono pre
For now, just would like to know how to implement using a resistor

 

[SY]

That depends. What circuit are you putting it in?

If you know the voltage across the CCS, you can calculate a resistor from R = V/I.

 

[Audiohifi]

CCS is to feed a shunt regulator for a preamp supply
So just measure the voltage across input and VR output.
Remove everthing that is shown in my schematic, Right?

 

[SY]

Pretty much, yes. Presumably, the CCS was sized to be twice the maximum expected current. If the raw supply has any sag under load, take that into account in the Ohm's Law calculation.

 

[Audiohifi]

Thank you SY for your explanation. Is that simple, hopefully it will sound better than
LM317T CCS

 

[Audiohifi]

If I remove the whole ccs circuit including mosfet, zener, resisors, etc and replace with a resistor, would not the circuit becomes ordinally current flow and not constant current flow? Just like a plate resistor.
Or I just replace only the LM317 after measuring the voltage across it
This tweak was discussed in Audio Asylum for the Super Regulator sold by Vacuum State,
but the exact method was given through PM
Glad to know how exactly it is done

 

[Audiohifi]

Schematics

 

[SY]

If I remove the whole ccs circuit including mosfet, zener, resisors, etc and replace with a resistor, would not the circuit becomes ordinally current flow and not constant current flow?

Yes. You lose most of the benefit of the CCS by doing this. I'm still not sure of the motivation, but I suspect Allen Wright is spinning in his grave.