Quick question: parallel LM317

maxlorenz · 8th December 2006, 04:15 PM

Hi,
I run a multi TDA1543DAC. I have some HF noise. One of the possible sources that I want to discard is noise generated by the LM317 regulator running too hot or near/over its current limit.
Typical max I for TO-220 is 1.5A and limit is 1.8A.

I made a test regulator consisting of two units with its pins soldered in parallel and they keep the desired Vout with only the standard pair of R.

By this mean I want to make that each reg passes half the current and *possibly* works more quietly

Does anybody see any inconvenient to this approach?

Thanks in advance...
M

jackinnj · 8th December 2006, 04:40 PM

it's just a little expensive to do it that way, but National Semi shows it in their product folder. (i have done this with their switching regulators --- just stacking one on top of the other.)

the amount of heat which can be dissipated in one of these regulators is a function of current times the differential between in put and output voltages.

pinkmouse · 8th December 2006, 04:41 PM

Would it be less noisy to use a meaty pass transistor?

jackinnj · 8th December 2006, 05:18 PM

it may be less noisy to have the two references operating -- but I haven't demonstrated this (and don't want to spend the time doing so).

maxlorenz · 8th December 2006, 07:17 PM

Thanks guys

I just wanted to be sure...

Quote:

National Semi shows it in their product folder.

Oh! I missed that, sorry...

Quote:

Would it be less noisy to use a meaty pass transistor?

A good friend designed a circuit for this application but I haven't got all the parts needed

Anyway, I think I'll learn in the attempt

Best regards,
M

jcx · 8th December 2006, 08:01 PM

Sorry guys but you're all wrong

you may get lucky but you shouldn't literally parallel pins of a pair of feedback amplifiers -which is what the Vregs are

if the internal Vrefs, loop gains don't match very exactly then the low impedance outputs will not share the load equally, with the Vregs only being able to source current at least it may not blow up like opamp or chip amp outputs tied together without sharing/limiting series R, but likely one reg is supplying 90% of the current

pinkmouse' approach is fine if you have a spare ~ 1 Volt of headroom

maxlorenz · 8th December 2006, 08:14 PM

Mmmhh...thanks, I'll study it again.

maxlorenz · 11th December 2006, 03:22 AM

Hi Jcx,
You were right, of course.
I did the test. I can't measure current but the new paralelled reg is hotter than the ancient: 58ºC v/s 38ºC, meaning, I guess that one is doing all the task.

The HF noise is still there, so it is comming from other place.
I would say music is clearer ...but I'm not sure.

As I can't source parts easilly, would it be worthy if I reproduce the regulator circuit, to end with two paralelled paths?
Will they pass a comparable current?

Thanks for your help,
M

BWRX · 11th December 2006, 03:48 AM

You could try this circuit http://www.diyaudio.com/forums/showt...45#post1005645 if you want better performance and have a beefy NPN or N channel FET handy.

maxlorenz · 11th December 2006, 04:17 AM

Thanks BWRX,
I'll check my box...

8th December 2006, 04:15 PM	#1
maxlorenz diyAudio Member Join Date: Oct 2003 Location: osorno , Chile	Quick question: parallel LM317 Hi, I run a multi TDA1543DAC. I have some HF noise. One of the possible sources that I want to discard is noise generated by the LM317 regulator running too hot or near/over its current limit. Typical max I for TO-220 is 1.5A and limit is 1.8A. I made a test regulator consisting of two units with its pins soldered in parallel and they keep the desired Vout with only the standard pair of R. By this mean I want to make that each reg passes half the current and possibly works more quietly Does anybody see any inconvenient to this approach? Thanks in advance... M __________________ Cheapest horn speakers: https://picasaweb.google.com/lh/phot...eat=directlink

8th December 2006, 04:41 PM	#3
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Would it be less noisy to use a meaty pass transistor? __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

8th December 2006, 08:14 PM	#7
maxlorenz diyAudio Member Join Date: Oct 2003 Location: osorno , Chile	Mmmhh...thanks, I'll study it again. __________________ Cheapest horn speakers: https://picasaweb.google.com/lh/phot...eat=directlink

11th December 2006, 03:22 AM	#8
maxlorenz diyAudio Member Join Date: Oct 2003 Location: osorno , Chile	Hi Jcx, You were right, of course. I did the test. I can't measure current but the new paralelled reg is hotter than the ancient: 58ºC v/s 38ºC, meaning, I guess that one is doing all the task. The HF noise is still there, so it is comming from other place. I would say music is clearer ...but I'm not sure. As I can't source parts easilly, would it be worthy if I reproduce the regulator circuit, to end with two paralelled paths? Will they pass a comparable current? Thanks for your help, M __________________ Cheapest horn speakers: https://picasaweb.google.com/lh/phot...eat=directlink

11th December 2006, 03:48 AM	#9
BWRX diyAudio Moderator Emeritus Join Date: Jan 2005 Location: Pennsylvania	You could try this circuit http://www.diyaudio.com/forums/showt...45#post1005645 if you want better performance and have a beefy NPN or N channel FET handy. __________________ Brian


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8th December 2006, 04:40 PM	#2
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	it's just a little expensive to do it that way, but National Semi shows it in their product folder. (i have done this with their switching regulators --- just stacking one on top of the other.) the amount of heat which can be dissipated in one of these regulators is a function of current times the differential between in put and output voltages.

8th December 2006, 05:18 PM	#4
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	it may be less noisy to have the two references operating -- but I haven't demonstrated this (and don't want to spend the time doing so).

8th December 2006, 08:01 PM	#6
jcx diyAudio Member Join Date: Feb 2003 Location: ..	Sorry guys but you're all wrong you may get lucky but you shouldn't literally parallel pins of a pair of feedback amplifiers -which is what the Vregs are if the internal Vrefs, loop gains don't match very exactly then the low impedance outputs will not share the load equally, with the Vregs only being able to source current at least it may not blow up like opamp or chip amp outputs tied together without sharing/limiting series R, but likely one reg is supplying 90% of the current pinkmouse' approach is fine if you have a spare ~ 1 Volt of headroom

11th December 2006, 04:17 AM	#10
maxlorenz diyAudio Member Join Date: Oct 2003 Location: osorno , Chile	Thanks BWRX, I'll check my box... __________________ Cheapest horn speakers: https://picasaweb.google.com/lh/phot...eat=directlink

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