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Old 26th November 2003, 03:41 AM   #1
name773 is offline name773  United States
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Lightbulb Power Supply question

hi, i had just built a gilmore amp, but i tried using only the lm317/337 regulators and not the opamps (bad idea), $8/chip and 4 chips was a bit much. the balance was a tad off, so here's a slightly cheaper idea that combines Mr. Elliott's shunt regulator (here, at bottom) and the lm317/337 preregulators from Mr. Gilmore's design.
schematic

do you think it will work? and are there any ideas for improvement?
the parts are on their way here.
thanks in advance
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Old 26th November 2003, 06:08 AM   #2
Steven is offline Steven  Netherlands
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Hi name773,

You will blow your transistors in this way. The zeners and the Vbe of the transistors (D5+Q1 and D6+Q2) will make 15.7V shunts, but the only current limiting is by the 317/337 preregulators, around 1A. You should use some resistor in front of the shunt regulator, like R1+R2 in the design of Rod Elliott. Just move your R5 and R6 to the left side of D5 and D6.
Or change the circuit around the 317 and 337 into floating current source and sink. Most datasheets of 317/337 show you how.

Steven
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Old 26th November 2003, 03:44 PM   #3
name773 is offline name773  United States
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thank you so much!
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Old 26th November 2003, 04:12 PM   #4
PRR is offline PRR  United States
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Steven is right: the 317/337s will run at maximum current, which surely is not what you want.

Why not just use the 317/337 as plain 15V regulators? If you don't like $8/chip, why get fancy at all? The 317/337 is a fine $2 regulator.
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Old 26th November 2003, 04:18 PM   #5
name773 is offline name773  United States
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yes it is, but this is for a Gilmore amp, and the psrr is lower than most designs. in fact, i tried that to begin with, but had offset issues. oh, the load is 187.5ma for both sides (one psu per channel). should R5-R6 be 44R? i'll try that first
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