Burning LM338

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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..
 
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.
 
Perhaps a silly question, but you dont happen to be trying two regulated supplies (4xLM338's) both running off of a single transformer ? I recently discovered this doesn't work, and from BWRX's explanation would make the "negative" acting LM338 run very hot... unless by "burns" you mean....... it explodes and stops working entirely..... I didn't have that problem :hot:
 
SY said:
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.


It is written on the drawing that the circuit is copyrighted by CarlosFM..

I have got no problems about wirings or groundings in the psu since it works unless I connect it to the amplifier.

I will chance the 1000uF caps with 2200uF to see if the problem is solved or not.. Also I will remove the soft start circuit..
 
markiemrboo said:
Perhaps a silly question, but you dont happen to be trying two regulated supplies (4xLM338's) both running off of a single transformer ? I recently discovered this doesn't work, and from BWRX's explanation would make the "negative" acting LM338 run very hot... unless by "burns" you mean....... it explodes and stops working entirely..... I didn't have that problem :hot:

No, I have just one regulated supply:)
 
OK. I have solved the problem, the poles of the supply caps just before the LM3886s are connected wrongly on the negative rail:smash: :smash: :smash: I corrected these but forgot the soft start circuit and there was a nice fireworks show inside my listening room:D

Now everything about the supply works fine, I got right voltages at every node.. However still there is no sound:bawling: Is there a way that I can understand If the LM3886 chips are burned or not?
 
SY said:
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.

I thought it might be the intention, but when things are blowing up it's as well to check. ;)

I'd describe it as "two similar 338-regulated DC supplies, taken from separate transformer secondaries, finally connected in series with a 'ground' rail taken from the mid-point" avoiding that '338 on the negative' ambiguity.

But then, I'm a pedant. :angel:
 
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