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Old 26th January 2008, 08:21 PM   #21
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Hi guys,

I have read this thread with great interest. You talk about over- and under-compensation.

But what is in your opinion the optimal figure, per degree C measured in mV over one of the emitter resistors?
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Old 27th January 2008, 06:06 AM   #22
roender is offline roender  Romania
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Quote:
Originally posted by revintage
Hi guys,

I have read this thread with great interest. You talk about over- and under-compensation.

But what is in your opinion the optimal figure, per degree C measured in mV over one of the emitter resistors?

0mV/C, but this is impossible!
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Old 27th January 2008, 07:46 AM   #23
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Ha,ha,ha!
Allready knew that answer. Please come back to Leachamp reality!

Letīs change optimal to practical. My guess is somewhere between -0,1mV/C to -0,5mV/C.
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Old 27th January 2008, 09:24 AM   #24
AndrewT is offline AndrewT  Scotland
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Hi,
The generally recommended range of Vre on the output transistors is 15mV to 25mV to maintain optimum ClassAB bias.
If this were rigorously applied for all operating conditions, from warm up through low temperature use through to cooling down after hard use then simply applying that 10mV range over 60Cdegree requires 0.17mV/C.
I quite like the idea of slight over compensation to automatically reduce bias as temperature rises so that gives us Tcomp<= -0.17mV/C. However for quiescent range testing I would half that requirement to -<0.1mV/C and the little bit of spare we have, try to keep within that 15mV to 25mV even for transient junction temperatures that heat monitoring can never exactly follow.

Any other thoughts?
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regards Andrew T.
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Old 28th January 2008, 06:14 AM   #25
roender is offline roender  Romania
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Quote:
Originally posted by revintage
Ha,ha,ha!
Allready knew that answer. Please come back to Leachamp reality!

Letīs change optimal to practical. My guess is somewhere between -0,1mV/C to -0,5mV/C.
You will never achieve that with high dynamic signal transients and without temperature sensing device in close proximity with power die. The key is ThermalTrack technology or something similar.
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Old 28th January 2008, 06:23 AM   #26
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Quote:
Originally posted by roender


You will never achieve that with high dynamic signal transients and without temperature sensing device in close proximity with power die. The key is ThermalTrack technology or something similar.
, the thread is about ThermalTrak isnīt it?
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Old 28th January 2008, 06:26 AM   #27
roender is offline roender  Romania
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I beg your pardon !?
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Old 28th January 2008, 06:35 AM   #28
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We where discussing ThermalTrak in the Leach amp. I asked about over or under compensation referreing to that. So I recconed ThermalTrak was already thought for. Nothing to get upset about .
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Old 28th January 2008, 07:51 AM   #29
roender is offline roender  Romania
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Quote:
Originally posted by revintage
We where discussing ThermalTrak in the Leach amp. I asked about over or under compensation referreing to that. So I recconed ThermalTrak was already thought for. Nothing to get upset about .
Lars,

Please give us your opinion about class B thermal compensation using ThematTrack devices and I'll see if I have someting to add.

Thank you,
Mihai
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Old 28th January 2008, 08:50 AM   #30
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Hi Mihai,
Sorry if you thought I was unfriendly! You must have misunderstood it all. You made a joke of my initial question and I joked back.

I had no opinion, because of that I made the question(with temp comp and ThermalTrak in mind):

"But what is in your opinion the optimal figure, per degree C measured in mV over one of the emitter resistors?" After your first answer I changed "optimal" to "practical".

As 0mV/C, as you say, is impossible there must be some figures below that that could be recommended.

I got an answer from AndrewT that gave me some insight but hopefully you can view it from some other angle to make it even more clear.

Brgds
Lars
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