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Old 26th June 2011, 03:39 PM   #1
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Default LM317T CCS Improvement

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
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File Type: doc ccs317.doc (26.0 KB, 232 views)
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Old 26th June 2011, 04:33 PM   #2
AndrewT is online now AndrewT  Scotland
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Is this a -ve supply?
Where is the input?
Where is the common?
Is the arrow head the output?
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Old 27th June 2011, 05:23 AM   #3
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Positive supply
arrow is the input
VR goes to the shunt regulator
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Old 27th June 2011, 11:12 AM   #4
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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.
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Old 27th June 2011, 12:20 PM   #5
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Quote:
Originally Posted by SY View Post
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: His Master's Noise: A Thoroughly Modern Tube Phono Preamp

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.
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Old 27th June 2011, 12:31 PM   #6
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Quote:
Originally Posted by SY View Post
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?
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Old 27th June 2011, 12:31 PM   #7
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$1-1.50, depending on quantity.
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Old 27th June 2011, 12:33 PM   #8
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Ah, so you're being robbed on the LM317 then.
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Old 27th June 2011, 12:49 PM   #9
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50 cents from a distributor who's unlikely to pawn off counterfeits.
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Old 27th June 2011, 12:51 PM   #10
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The first price I pulled up for the LM317T (manu ST) is 26.5cents. Can your disty manage 13cents ya reckon?
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