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Subject: Re: Bad LM338K? Extra question ...
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Sat, 14 Dec 2002 14:01:26 GMT
NNTP-Posting-Date: Sat, 14 Dec 2002 15:01:26 MET
Organization: Telenet Internet
Yes my LM338 was damaged ... replaced the LM ... and supply now works like a
"Christopher R. Carlen" wrote in message
> Werner wrote:
> > When I first got the PCB made up, I noticed that the heavy 10.000 uF
> > capacitor blew my fuse at the primary stage of my transformer ... I had
> > install something bigger than a 2 Amps fuse to survive the inbound
> > rush from the capacitor ... I did not learn about NTC resistors used to
> > prevent this till after this design :-(
> > Can this damage the LM338K? As the capacitor is located before the LM,
> > does not harm the LM? Or is this a faulty assumption? I've got the LM
> > protected by 2 diodes, one from the output to the input line and one
> > the adjust leg to the output leg.
> That won't damage the regulator, which only sees the filtered voltage
> from the capacitor, which slowly rises to the final peak value with no
> There are basically these possibilities:
> 1. Raw DC voltage is drooping at the input to the regulator. It isn't
> enough to just know that you have a 10A transformer. You must monitor
> the raw DC with a voltmeter while changing the load on the reg. output
> to be sure it stays at least about 3V higher than the desired load
> voltage at all times.
> 2. The regulator is overheating. You have indicated that it doesn't
> appear to be very hot so...
> 3. The regulator is oscillating. You can only determine this with an
> oscilloscope. Do you have an oscilloscope and what is it telling you?
> 4. The regulator is broken. Try another one.
> Good day.
> Christopher R. Carlen
> Principal Laser/Optical Technologist
> Sandia National Laboratories CA USA
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