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From: stevem@specialix.co.uk (Steven Murray)
Newsgroups: sci.electronics
Subject: Re: Voltage Regulators in Parallel
Message-ID: <1991May17.154852.24280@specialix.co.uk>
Date: 17 May 91 15:48:52 GMT
References: <1991May16.165916.12600@tc.fluke.COM>
Organization: Specialix International, London
Lines: 34

ferguson@tc.fluke.COM (Ed Ferguson) writes:

>I'm adding voltage regulation to my audio amp to improve performance.
>Vout is +/- 28 V and the amp draws 3A on each peak.  National makes an 
>adjustable 3A positive regulator (LM150) but I don't see a 3A negitive
>adjustable regulator offered.

>Could two LM317Ts (1.5A each) and two LM337Ts (1.5A each) operate in
>parallel to supply the +/- rails at 3A?  Or is a regulator with
>a series pass transistor the better way to get more current?

>Ed Ferguson

Sure! But you need to share the current between them with resistors.
Typically you would put a 0.1-0.2 ohm in each output lead, then tie.
Have a look at the specs and apps in the data book for the devices.
One circuit you probably won't see in the data book that does work
is a couple of LM317's set up with output adjustment resistors,
followed by load sharing resistors.  You DO get output variation -
but not a lot.  0.2 ohm resistors will give you 0.3v load variation
from 0 to 3A.  There does seem to be a 3 amp adjustable reg: LM333T.
Anyway, you might want to watch out for heat dissapation - something
that's easily overlooked.  You might end up deciding to use 3 regs
on each side, just to be really sure the heat doesn't exceed ratings.
I prefer using regs to Transistors (except on large quantity work) -
a couple of extra pennies for smarter regulation.  Do put in all the
decouple caps and protection diodes recommended in the data sheets
too - its so nice to do projects once instead of twice!

-- 
Steven Murray
uunet!slxsys!stevem  stevem@specialix.co.uk
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