Burning LM338

seftali · 21st February 2007, 08:53 PM

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..

Minion · 21st February 2007, 08:55 PM

The Pin out on the LM317 and LM338 are different so make sure you have taken that into account.....

Just a Thought.....

seftali · 21st February 2007, 09:11 PM

Although I could not understand the relationship between LM317 and LM338, their pin out on National Semi. website is the same

imperfectcircle · 21st February 2007, 09:49 PM

The pin out looks the same to me

ADJ OUT IN

seftali · 21st February 2007, 09:54 PM

Can the soft start circuit be the problem? If yes, why why why?

cpemma · 21st February 2007, 11:17 PM

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?

Minion · 22nd February 2007, 12:16 AM

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)....

seftali · 22nd February 2007, 02:59 AM

Quote:

Originally posted by cpemma

The LM338 is a 5A positive regulator...

What's your circuit?

(copyrighted drawing removed by moderators)

SY · 22nd February 2007, 03:15 AM

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.

BWRX · 22nd February 2007, 03:22 AM

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

21st February 2007, 08:53 PM	#1
seftali diyAudio Member Join Date: Oct 2006	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..

22nd February 2007, 03:15 AM	#9
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	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. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

22nd February 2007, 03:22 AM	#10
BWRX diyAudio Moderator Emeritus Join Date: Jan 2005 Location: Pennsylvania	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 __________________ Brian

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21st February 2007, 08:55 PM	#2
Minion diyAudio Member Join Date: May 2006	The Pin out on the LM317 and LM338 are different so make sure you have taken that into account..... Just a Thought.....

21st February 2007, 09:11 PM	#3
seftali diyAudio Member Join Date: Oct 2006	Although I could not understand the relationship between LM317 and LM338, their pin out on National Semi. website is the same

21st February 2007, 09:49 PM	#4
imperfectcircle diyAudio Member Join Date: Jan 2005 Location: nyc	The pin out looks the same to me ADJ OUT IN

21st February 2007, 09:54 PM	#5
seftali diyAudio Member Join Date: Oct 2006	Can the soft start circuit be the problem? If yes, why why why?

22nd February 2007, 12:16 AM	#7
Minion diyAudio Member Join Date: May 2006	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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