Munted LM4780 freebee

enzedone · 14th June 2006, 02:18 AM

I wonder if anyone else has ever had one of their samples from Nat. explode...

I have just finished hooking up my LM4780 amp and it has just fried the chips.

I checked over and over the supplies, and again afterwards. They are correct, but the chips are toast. No problems with the caps or anything else.
Supply is 36.8v.

This is my third one, but my first LM4780. Boards are from Daniel, I wonder if i set it up right, for parallel?

I have never had anything go wrong before, oh well just as well the chips were samples.

enzedone · 14th June 2006, 02:20 AM

This is my layout, probably can't see much from these pics

enzedone · 14th June 2006, 02:23 AM

Another pic of the front..............

taj · 14th June 2006, 03:26 AM

Daniel has mentioned that the LM4780 chips need to be insulated from the heatsink/ground or they will blow. Could that be the problem?

..Todd

enzedone · 14th June 2006, 03:39 AM

Dohhhhhhhhhhhhhhhhhhhhhh!

Yes that is the exact problem.............

I will just have to try and get another set from somewhere.........

Cheers Taj

enzedone · 14th June 2006, 03:41 AM

God it makes you angry when you do something sooooooooooo simple and stupid.....

taj · 14th June 2006, 04:27 AM

Well if it makes you feel any better, I would have done the same thing if I hadn't seen Daniel's warning. His website schematics were updated recently to mention this.

..Todd

zenon · 14th June 2006, 04:28 AM

so where was the err? you shouldn't have used screws to hold it together??? please be more specific so I don't make the same simple mistake.

taj · 14th June 2006, 04:34 AM

Well you have to use an insulator between the chip and heatsink, and also use the bushings that insulate the screws from the chip.

I suppose you could, alternatively, insulate the heatsink from ground but this would be a little dangerous in terms of potential accidental shorts.

I'm pretty much a newbie so I can't offer any more details than that. I'm sure the gurus can elaborate.

...Todd

enzedone · 14th June 2006, 04:41 AM

Next time I will just place an alluminium bar right across the two chips and then screw this down to the plate, this with cut any need to screw the chips directly. Plus of coarse the use of unsulation.

14th June 2006, 03:39 AM	#5
enzedone diyAudio Member Join Date: Nov 2004 Location: New Zealand	Insulation Dohhhhhhhhhhhhhhhhhhhhhh! Yes that is the exact problem............. I will just have to try and get another set from somewhere......... Cheers Taj __________________ I realized that a major part of my job was to figure out how to use technology control to create economic force, or leverage, such that money and business flowed in Microsoft's direction” — Alex St.John, father of DirectX.

14th June 2006, 03:41 AM	#6
enzedone diyAudio Member Join Date: Nov 2004 Location: New Zealand	Insulation God it makes you angry when you do something sooooooooooo simple and stupid..... __________________ I realized that a major part of my job was to figure out how to use technology control to create economic force, or leverage, such that money and business flowed in Microsoft's direction” — Alex St.John, father of DirectX.

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14th June 2006, 03:26 AM	#4
taj diyAudio Member Join Date: Feb 2005	Daniel has mentioned that the LM4780 chips need to be insulated from the heatsink/ground or they will blow. Could that be the problem? ..Todd

14th June 2006, 04:27 AM	#7
taj diyAudio Member Join Date: Feb 2005	Well if it makes you feel any better, I would have done the same thing if I hadn't seen Daniel's warning. His website schematics were updated recently to mention this. ..Todd

14th June 2006, 04:28 AM	#8
zenon diyAudio Member Join Date: Nov 2004 Location: here	so where was the err? you shouldn't have used screws to hold it together??? please be more specific so I don't make the same simple mistake.

14th June 2006, 04:34 AM	#9
taj diyAudio Member Join Date: Feb 2005	Well you have to use an insulator between the chip and heatsink, and also use the bushings that insulate the screws from the chip. I suppose you could, alternatively, insulate the heatsink from ground but this would be a little dangerous in terms of potential accidental shorts. I'm pretty much a newbie so I can't offer any more details than that. I'm sure the gurus can elaborate. ...Todd

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