LM4780 Heat problem

Niila · 29th November 2006, 01:23 PM

Hello!

Im building a LM4780 stereo amplifier as my schoolwork. Im using one chip for two channels with 36V rails. The problem is that it produces too much heat. I could only try it for like 5 seconds before it was too hot for my fingers. Of course i used heatsink.

I used signal generator for testing.. I have double checked everything and there should not be any problems. I used the schematic found in the datasheet.

Heres some pictures:

Picture 1

Picture 2

Picture 3

Thank you!

halo0925 · 29th November 2006, 02:00 PM

What size heat sink?
Do you have a scope? check for oscillation.

Niila · 30th November 2006, 08:51 AM

Without input the amp doesnt oscillate. Heatsink is well big enough.

Niila · 30th November 2006, 09:23 AM

Its just that it gets too hot in like 5 to 10 seconds when input signal is connected.

Even if i touch the input wires with my fingers, the amp takes 200mA current and gets hot.

The sine signal in scope looks very "fat", but clean. I will take some pictures tomorrow.

Nordic · 30th November 2006, 10:50 AM

Use a kitchen towel to wipe that flux off the solder with some acetone. I'm pretty sure I see some solder droplets crossing rails or bridgeing them close enough to cause problems with capacitive coupling. like the 6th pin from the left on the botton row in the second picture also the 3rd from left in that row, looks bent suspiciously close to the ground plane.

space · 1st December 2006, 07:57 AM

If the signal looks "fat", isn't that an indication of oscillation?

space

pinkmouse · 1st December 2006, 08:02 AM

Yes, and it may well be beyond the resolution of your scope. What happens with the input shorted to earth?

es44 · 1st December 2006, 09:17 AM

To me it looks like Nordic has a point. I don't like the looks of those solderings either. Some heavy solder droppings scattered all around, and i'm not sure if my eyes are fooling me, but to me it looks like a dry solder at picture 2, second soldering from beneath at the far right side.
Resolder, and clean up, that may do it.

Also a good magnifying glass could be handy.

Good luck
Ebbe

Niila · 1st December 2006, 11:29 AM

There is no solder droppings really.. its just some dirt sticked in to pcb. Some of the joints arent so good because the pads are too small. There should not be any flux left on pcb.

Anyway i will try to solder it once more. Thanks for the tips..

I used electronic microscope to solder the chip in the first time

Heres a screenshot..

runebivrin · 1st December 2006, 12:33 PM

Whoa, that looks like major oscillation to me! What's your gain?

Rune

29th November 2006, 01:23 PM	#1
Niila diyAudio Member Join Date: Aug 2004 Location: Oulu	LM4780 Heat problem Hello! Im building a LM4780 stereo amplifier as my schoolwork. Im using one chip for two channels with 36V rails. The problem is that it produces too much heat. I could only try it for like 5 seconds before it was too hot for my fingers. Of course i used heatsink. I used signal generator for testing.. I have double checked everything and there should not be any problems. I used the schematic found in the datasheet. Heres some pictures: Picture 1 Picture 2 Picture 3 Thank you!

29th November 2006, 02:00 PM	#2
halo0925 diyAudio Member Join Date: Aug 2006	Heat What size heat sink? Do you have a scope? check for oscillation.

1st December 2006, 08:02 AM	#7
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Yes, and it may well be beyond the resolution of your scope. What happens with the input shorted to earth? __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

1st December 2006, 12:33 PM	#10
runebivrin diyAudio Member Join Date: Jul 2003 Location: Huddinge, Sweden	Whoa, that looks like major oscillation to me! What's your gain? Rune __________________ Do wizards use spell checkers?

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

30th November 2006, 08:51 AM	#3
Niila diyAudio Member Join Date: Aug 2004 Location: Oulu	Without input the amp doesnt oscillate. Heatsink is well big enough.

30th November 2006, 09:23 AM	#4
Niila diyAudio Member Join Date: Aug 2004 Location: Oulu	Its just that it gets too hot in like 5 to 10 seconds when input signal is connected. Even if i touch the input wires with my fingers, the amp takes 200mA current and gets hot. The sine signal in scope looks very "fat", but clean. I will take some pictures tomorrow.

30th November 2006, 10:50 AM	#5
Nordic diyAudio Member Join Date: Sep 2005	Use a kitchen towel to wipe that flux off the solder with some acetone. I'm pretty sure I see some solder droplets crossing rails or bridgeing them close enough to cause problems with capacitive coupling. like the 6th pin from the left on the botton row in the second picture also the 3rd from left in that row, looks bent suspiciously close to the ground plane.

1st December 2006, 07:57 AM	#6
space diyAudio Member Join Date: Jan 2004 Location: Oslo - Norway	If the signal looks "fat", isn't that an indication of oscillation? space

1st December 2006, 09:17 AM	#8
es44 diyAudio Member Join Date: Apr 2005 Location: Fredericia, DK	To me it looks like Nordic has a point. I don't like the looks of those solderings either. Some heavy solder droppings scattered all around, and i'm not sure if my eyes are fooling me, but to me it looks like a dry solder at picture 2, second soldering from beneath at the far right side. Resolder, and clean up, that may do it. Also a good magnifying glass could be handy. Good luck Ebbe

1st December 2006, 11:29 AM	#9
Niila diyAudio Member Join Date: Aug 2004 Location: Oulu	There is no solder droppings really.. its just some dirt sticked in to pcb. Some of the joints arent so good because the pads are too small. There should not be any flux left on pcb. Anyway i will try to solder it once more. Thanks for the tips.. I used electronic microscope to solder the chip in the first time Heres a screenshot..

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
problem with heat of MOSFET	yanuarbob5150	Class D	8	9th February 2009 03:11 PM
heat sink problem	k1jroth	Solid State	12	24th March 2006 07:34 AM
heat pipe problem	B.I.G	Chip Amps	4	29th November 2004 05:42 PM
heat problem or not ??	arold19	Pass Labs	11	3rd May 2004 01:37 PM
Yet another heat sink problem	OliverD	Pass Labs	10	16th October 2003 05:29 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read