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Old 7th January 2006, 08:17 AM   #1
jlm is offline jlm  France
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Default LM317 and LM337 Regulators in parallel

Hello,

I search a schematic to put in parallel 2 LM317 and 2 LM337

and another schematic with 3 LM317 and 3 LM337 in parallel .

Thank you for your answers

Best regards.

jlm
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Old 7th January 2006, 10:17 AM   #2
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for cost reasons, current carrying capacity is often boosted by using a pass transistor ('2905, '3055) around the regulator instead of paralleling devices. you can parallel the devices, however -- it's just a few centimes more expensive.

If you decide to parallel these regulators, place a small resistor (0.1 or 0.22 ohm) in series with each output. This will make them happier in sharing the current.

National Semi's product folder on the LM317 shows how to boost current capacity -- they use a super-matched pair of transistors (because it was a device they manufactured) -- you can use MJE2955, 3055.
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Old 7th January 2006, 10:34 AM   #3
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What are you going to use these regulators for? Maybe we can suggest something better/different?
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Old 7th January 2006, 04:03 PM   #4
Onra is offline Onra  Germany
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Hi,
for the positive supply you can replace 3 LM317 by one LM338T or K.
The T-version comes in a TO220-case and K means TO3.
The negative branch will become more difficult, because there are afaik no regulators of more than 3 A.
In the LM317 and LM337 datasheet (NatSemi) are applications with paralleled devices to increase their current capability.
Onra
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Old 7th January 2006, 04:20 PM   #5
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Quote:
Originally posted by Onra
The negative branch will become more difficult, because there are afaik no regulators of more than 3 A.
Linear Technologies LT1185 negative regulator will do 3 amps.
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Old 7th January 2006, 04:50 PM   #6
lineup is offline lineup  Sweden
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Quote:
Originally posted by jackinnj
for cost reasons, current carrying capacity is often boosted by using a pass transistor ('2905, '3055)
...'
-- you can use MJE2955, 3055.
this is the way I would prefer, too
for the positive LM317 you use a PNP TO3 transistor
for the negative LM337 you use a NPN TO3 transistor

Here is link to such a project with description:
LM317T Voltage Regulator with Pass Transistor

Click the image to open in full size.
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Old 7th January 2006, 07:48 PM   #7
Onra is offline Onra  Germany
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Hi,
same post appears at "electronics and parts".
Is it possible to concentrate these posts to one?
Onra
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Old 7th January 2006, 08:08 PM   #8
Danko is offline Danko  Hungary
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It's in the "powersupply designing" section.

Onra, ask one of the moderators, to merge theese two topics.
For example Sy, or pinkmouse :-)

Best regards, Danko
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