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NNTP-Posting-Date: Wed, 11 Dec 2002 14:31:13 -0600
From: "john walton"
Subject: Re: Bad LM338K?
Date: Wed, 11 Dec 2002 15:30:50 -0500
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First, the big adjustable regulators the Vtrim should be adjusted with a
load of at least, 3.5 to 10 mA.
The performance guaranteed is given when Vout - Vin <= 10V, so check to
make sure that the input to the regulator isn't a lot more than this (are
you sure it's only 35 VDC?)
"Werner" wrote in message
> Hi guys,
> I'm looking for a answer to a puzzling question ...
> I've build a power supply from a LM338K (TO3) with a 10.000 uF and a 100uF
> capacitor on the input line and a 1uF and a 0.1uF capacitor to output a
> fixed 24 volts DC supply.
> I 've got a 220 ohm resistor between LM output the adjust of the LM, and a
> 4k7 trimpot to the ground ... which I adjust to 24 VDC (with almost no
> ... the transformer delivers 35 volts DC to the input of the LM (no
> The transformer is rated min. 10 Amps.
> All correct so far? Fact is that it allows me to drive small loads ... eg.
> power resistor 51 Ohm ... 24 volts output is kept ... resistor warms up
> no problem ...
> Now I put a second 51 Ohm resistor in parallel to the first resistor ...
> the output voltage of the circuits drops 4 volts (to 19-20 volts), to the
> best of my knowledge this is way under the power specs of the LM338, as it
> should be able to drive 5 Amps with input-output difference of 11 volts?
> How can this be explained? At this state even adjusting the trimpot has no
> effect on the voltages anymore ... it's like the regulator has found a
> state" and does not want to provide 24 volts ... it almost does not
> any heat ... could it be damaged? Or is there a simpler explanation?
> Many thanks,
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