mosfet getting hot !!!

djronbxs · 31st May 2006, 06:54 PM

Hi,

I have an amplifier and it has 4 mosfets which are paired (2sc3182 & 2sa1265) after a while 1 pair of these mosfet are getting hot the others get normal hot. can somebody tell me how to adjust the quescient current and how to calculate it or what is wrong please ?

thanks
ronald

jan.didden · 31st May 2006, 06:59 PM

... schematic diagram?

MikeW · 31st May 2006, 07:26 PM

Are they MOSFET or Bipolar?
http://www.cpcares.com/pdf/2SC3182.PDF

djronbxs · 1st June 2006, 06:28 AM

i think they are MOSFET.

no i dont have chematics !

AndrewT · 1st June 2006, 06:46 AM

Hi,
is that a two channel (stereo) amplifier?

One pair of output devices in each channel?

Compare the hot channel to the cooler channel.

ilimzn · 1st June 2006, 09:22 AM

Quote:

Originally posted by djronbxs
i think they are MOSFET.
no i dont have chematics !

You may think what you want, but they are not.
MikeW gave you a polite hint, and even provided you with a datasheet link, I'll give you a less polite one: 2SA, 2SB, 2SC, 2SDxxxx are all bipolar transistors, marked according to japanese standards (JEIA). 2SA and 2SB are PNP, 2SC and 2SD are NPN. Under the same standard, (MOS)FETs are marked 2SJxxxx (P ch) and 2SKxxxx (N ch).
Poking inside amps without knowing the basics is asking for trouble!

djronbxs · 1st June 2006, 11:00 AM

yes it is a stereo amplifier, with a pair on each side.

it is not getting very hot when idle but when i play for a short time it gets hot !

how can i measure the quiscent current please ? i have digital meter.

thanks

AndrewT · 1st June 2006, 11:32 AM

Hi,

Quote:

it is not getting very hot when idle but when i play for a short time it gets hot

that seems a bit odd.

I cannot see a quiescent adjustment curing this problem.

Could it be severe instability? causing hiFreq oscillation?

Or,

could there be a short on the output lead that carries current only when signal is amplified?

djronbxs · 1st June 2006, 07:45 PM

what you mean ? why it isnt quiscent current prob ?

anatech · 1st June 2006, 08:01 PM

Hi djronbxs,
AndrewT is right. If it was a quiescent current problem, the transistors woud get hot while idling (quiescent state). It does appear to be a load related problem.

Have you tried swapping the speaker leads (amp turned off!).

-Chris

31st May 2006, 06:54 PM	#1
djronbxs diyAudio Member Join Date: May 2006	mosfet getting hot !!! Hi, I have an amplifier and it has 4 mosfets which are paired (2sc3182 & 2sa1265) after a while 1 pair of these mosfet are getting hot the others get normal hot. can somebody tell me how to adjust the quescient current and how to calculate it or what is wrong please ? thanks ronald

31st May 2006, 06:59 PM	#2
jan.didden diyAudio Member Join Date: May 2002 Location: Great City of Turnhout, Belgium Blog Entries: 6	... schematic diagram? __________________ It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts - Sherlock Holmes Check out Linear Audio Vol 5!

31st May 2006, 07:26 PM	#3
MikeW diyAudio Member Join Date: Sep 2002 Location: North of Boston	Are they MOSFET or Bipolar? http://www.cpcares.com/pdf/2SC3182.PDF __________________ MikeW

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1st June 2006, 06:28 AM	#4
djronbxs diyAudio Member Join Date: May 2006	i think they are MOSFET. no i dont have chematics !

1st June 2006, 06:46 AM	#5
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, is that a two channel (stereo) amplifier? One pair of output devices in each channel? Compare the hot channel to the cooler channel.

1st June 2006, 11:00 AM	#7
djronbxs diyAudio Member Join Date: May 2006	yes it is a stereo amplifier, with a pair on each side. it is not getting very hot when idle but when i play for a short time it gets hot ! how can i measure the quiscent current please ? i have digital meter. thanks

1st June 2006, 07:45 PM	#9
djronbxs diyAudio Member Join Date: May 2006	what you mean ? why it isnt quiscent current prob ?

1st June 2006, 08:01 PM	#10
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi djronbxs, AndrewT is right. If it was a quiescent current problem, the transistors woud get hot while idling (quiescent state). It does appear to be a load related problem. Have you tried swapping the speaker leads (amp turned off!). -Chris

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