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From: paul@axiom.UUCP (Paul O`Shaughnessy)
Newsgroups: net.analog,net.micro
Subject: Re: question about Lamda power supplies
Message-ID: <202@axiom.UUCP>
Date: Fri, 4-Apr-86 13:23:03 EST
Article-I.D.: axiom.202
Posted: Fri Apr  4 13:23:03 1986
Date-Received: Sat, 5-Apr-86 10:19:54 EST
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Organization: Axiom Technology, Newton MA
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Xref: linus net.analog:734 net.micro:12963


>From: jeffj@sfsup.UUCP (J.S.Jonas)

>[linears go hmmmmmmmmmm, but switchers go skeeeeeeeeeeee]

>I am using Lamda LUS-8-12 and LUS-9-5 power supplies.  Since these are
>switching power supplies, do I have to supply a minimum load?
>The built-in LED indicator seems to make it well behaved with no load.

No.  These Japanese manufactured switchers will operate correctly down
to no load.  However, they do this by reducing the duty cycle on the
converter transistor, and very near no load, the circuit may begin to
drop out entire cycles, effectively dropping the switching frequency.
The result is the audible 'skeeeeee' that you hear.  The practical
consideration is the noise on your AC line (EMI, etc) and DC output.
These are inexpensive supplies and they didn't blow the bank on filtering.
I used the LU series, and they worked fine.  I would stay away from much
of the rest of Lambda's line, particularly the LY, LN, and LO series.
The LU series can be second sourced by some models from Panasonic.

The power supplies which require a minimum load are typically high power
multichannel switchers in which a single magnetic core is used to 
provide power to all channels, so to ensure adequate current to the
secondary channels, you must have a minimum amount of activity on the
primary channel.

-----------------
  Paul O'Shaughnessy @ Axiom Technology, Newton, Massachusetts
  Home of the 'Management Team'      {ihnp4,utzoo}!linus!axiom!paul (uucp)
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