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Old 10th December 2006, 09:11 PM   #41
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by carpenter
lineup, I cut, pasted and saved your last discourse. Thanks; I'll build this amp at a later date when I'm done with my ZV7-T series.

Hey choky, that's a neat set of drafting symbols and will work great with "paint".

Life is great,

John

I'm lost in all this threads.......
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Old 10th December 2006, 09:41 PM   #42
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Old 11th December 2006, 10:51 PM   #43
lineup is offline lineup  Sweden
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I have had a look at your latest schematic
in this topic, Fuling ( man you are really UGLY, Fuling )

Here it is:
http://www.diyaudio.com/forums/attac...amp=1165697731


I think it looks good.
And you say it works, too

If you want to use higher voltage and/or currents = more power,
you can do some math, on the heat and temperature.
Ths way we can figure out what MOSFET to use.

TO220 are good and often fast and fairly low capacitance
But they have a limit how much power can be used.
At least before they start operation so bad, it will be distortion = bad sound.

TO247 and TO3 can take more powers.
But at the cost of less speed and more capacitance.
And will be a bigger load for input stage and so maybe
have a higher distortion level and be a bit slower.
-----------------------

Advice, if your math & calculations show, that TO220 can be used
within good margin of max temperature of transistor,
then use TO220.

But if the temperature of operation (junction temperature)
gets >=100 degrees, then I would step up to a bigger power transistor.
Because it is very probably this bigger device, would give less distortion, anyway.
------------------------


It is not too difficult to calculate what the junction temperature will be like.
Tyimo has learned this, by my instructions!

You have formulas here, and some examples:
http://www.diyaudio.com/forums/showt...04#post1069904
See this post, and the following posts!



Once you have the data of your heatsink
it is no advanced math. Only multiply and addition.

If you have not exact data of a big heasink, like a big piece of aluminium or Your amp Chassi,
then you can make a good guess,
by comparing WEIGHT, in KG, to other BIG heatsinks in ELFA catalog.
The value we want is like:
0.7 C/W.
( each watt will increase temperature 0.7 degrees C )
------------------------------------------------------------------------------

Link to ELFA heatsinks, with DATA:
http://www.elfa.se/elfa-bin/lt.pl?la...474382&1474384


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Old 11th December 2006, 11:09 PM   #44
flg is offline flg  United States
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I'm sorry guy's. I'm reading all this and I just have to ask the obvious With everything involved in a baby ZEN, with cascoding and all, why not build a ZV9 variant??? A Baby ZV9???
Less parts Probably less THD
I'm trying to build a slightly bigger ZV9 variant with my L Loaded thread
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Old 12th December 2006, 10:02 AM   #45
Fuling is offline Fuling  Sweden
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flg: ZV9 would be great, but I don´t have any power Jfets...

lineup: My new heatsinks are bigger than anything in the Elfa catalog, probably 0,25 degrees C/W so they are probably big enough, but as you say I´ll have a look at the "internal" thermal resistance of each mosfet.

Edit: 75645P has a junction-to-case thermal resistance of 0,48 C/W, while IRF540 has 1,1 C/W.
Seems like 75645P would be a good choice for everything except the gain transistor in the bigger version.
The pre-drilled holes in my heatsinks is another limiting factor, there´s a row of M3 tapped holes at 20 mm C-C, so if I use T0-220 devices I can use alu-oxide insulators but if I choose T0-247 I must use modified silicon tabs.
So, T0-220 it will be!
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Old 12th December 2006, 03:33 PM   #46
lineup is offline lineup  Sweden
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Quote:
Originally posted by Fuling

lineup: My new heatsinks are bigger than anything in the Elfa catalog, probably 0,25 degrees C/W so they are probably big enough, but as you say I´ll have a look at the "internal" thermal resistance of each mosfet.
....
The pre-drilled holes in my heatsinks is another limiting factor,
....
So, T0-220 it will be!
Such big heatsink is good for TO220 cooling.

Another good rule of the thumb, for the heatsink size itself:
At the total watt to cool from all devices placed on the heatsink
the heatsink should not be hotter than air around
with more than +40,+50 degrees



The formula using this rule would be (for 50 degrees C increase):
50 / Total Watt = heatsink required C/W

Say we want to cool total 100 watt running through transistors fitted on heatsink.
50/ 100Watt = 0.50 C/W

The temp of heatsink will be, at room temp = 25 C
25 + 50 = 75

-------------------------------
Of course if using the more strict value 40 C increase, 10 degrees more safety margin,
we would use formula:
40/100 Watt = 0.40 C/W heatsink (would give 25+40=65 C temp of a 0.40 C/W heatsink)


Other ways to use this rule of thumb:
Say we have an heatsink like 0.25 C/W.
How many watt for an increase of 40 degrees?
Yes,
40/0.25 = 160 Watt.
By this rule your heatsink should be good for cooling total 160 Watt, something.
----------------------------------

Now things aren't quite that easy.
Even if heatsink is only 65 C,
if we use transistors with too high C/W, the temp inside transistor
can be very high, even if heatsink is not more than 65 degrees.

But think is not problem in this case.
1.1 C/W is a good low value for TO220.

But some other TO220 has got 1.4 and 2.0 C/W .......
Like IRF610 and IRF9610 have higher values.



In fact is very easy to find out what value a TO220 has got.
Without datasheet!
You only need to know max effect, power for the transistor.
125/max power ~ C/W value.

for TO247:
150/max power ~ C/W value.

for TO3:
175/Transistor Max power Rating ~ C/W value.


The exact formula:
[Max junction temp of the package -25 (for room temp=25)] / Max Power Rating = C/W value.

TO220 - Max Junction temp 150.
150-25 = 125
As IRF540 probably is a 125 Watt transistor,
we get 125/125 ~1.0 C/W .... or as you say 1.1, more correct.


lineup
hope you got it
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Old 12th December 2006, 03:59 PM   #47
Fuling is offline Fuling  Sweden
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Thanks Lineup for the mathematical examples and formulas (erhm, guidelines at least)!

I just thought about a little detail: Let´s move this discussion to the correct thread:
Right mosfet in the right position?
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