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Old 21st February 2007, 08:53 PM   #1
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Default Burning LM338

Hi

I have just finished my gainclone.. The power supply is regulated(also snubberized) and working properly before connecting to the amplifier stage.. After connecting to the amplifier stage, the voltage regulator LM338 on the negative rail burns just in a few seconds.. But the positive rail works properly.. I double checked the connections and the output of negative regulator is not grounded.

I am using 1000uF and 100nF just before the LM3886 chips, also a 10K resistor - 47uF caps - 15K resistor network just before the mute pin for soft start.

What would be the problem? Thanks..
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Old 21st February 2007, 08:55 PM   #2
Minion is offline Minion  Canada
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The Pin out on the LM317 and LM338 are different so make sure you have taken that into account.....

Just a Thought.....
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Old 21st February 2007, 09:11 PM   #3
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Although I could not understand the relationship between LM317 and LM338, their pin out on National Semi. website is the same
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Old 21st February 2007, 09:49 PM   #4
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The pin out looks the same to me


ADJ OUT IN

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Old 21st February 2007, 09:54 PM   #5
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Can the soft start circuit be the problem? If yes, why why why?
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Old 21st February 2007, 11:17 PM   #6
cpemma is offline cpemma  United Kingdom
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Default Re: Burning LM338

Quote:
Originally posted by seftali
After connecting to the amplifier stage, the voltage regulator LM338 on the negative rail burns just in a few seconds.. But the positive rail works properly..
The LM338 is a 5A positive regulator...

What's your circuit?
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Old 22nd February 2007, 12:16 AM   #7
Minion is offline Minion  Canada
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Sorry...I got the LM338 Mixed up with the LM337....The LM317 and LM337 Have different Pin outs (Adj,Out,In, VS Adj,In,Out)....

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Old 22nd February 2007, 02:59 AM   #8
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Default Re: Re: Burning LM338

Quote:
Originally posted by cpemma


The LM338 is a 5A positive regulator...

What's your circuit?

(copyrighted drawing removed by moderators)
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Old 22nd February 2007, 03:15 AM   #9
SY is offline SY  United States
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I removed a copyrighted drawing. It's a regulator by CarlosFM.

The circuit is a 338 on the positive side and a 338 on the negative side with the output grounded and the negative rail taken from its normally common end. If the output of the second 338 isn't grounded, check your wiring; it should be.

Otherwise, disconnect the regulator and check the raw supplies. If they're OK, put a scope across the output of the negative regulator, power up, and see if it's oscillating.
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Old 22nd February 2007, 03:22 AM   #10
BWRX is offline BWRX  United States
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What's so special about his drawing? Is there a snubber on the output?

Look here for probably the exact same circuit: http://www.pedjarogic.com/gc/supplies.htm
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