Transistor Dissipation and Turbo Projects

[EUVL]

For your reference, free download :

http://www.linearaudio.net/images/stories/Didden LA V3 PK lr.pdf
http://www.diyaudio.com/forums/pass-labs/183362-f5x-euvl-approach-16.html#post3280044


Patrick

 

[ra7]

That was very helpful, Papa. Thanks! I like your other rule of thumb also: you should be able to keep your fingers on the heatsink for 10 seconds.

 

[el_mariachi]

I am sorry, but it is late and I am lost.

Tj = W * (Rj + Rc + Rh) + Ta
Tj = 16 * (1 + 1 + 2) + 25
Tj = 16 * 4 + 25
Tj = 64 + 25
Tj = 89

Where did 116 come from?

I know this is an old thread but i also find this confusing.
Maybe someone could explain a little further.

 

[diy_audio_fo]

I know this is an old thread but i also find this confusing.
Maybe someone could explain a little further.

You can model the thermal circuit as an electrical circuit [Thermal unit = Electrical unit]:

Thermal resistance (Rth) = R
Power (W)= I
Temperature (T)= V

From Ohm's law

V = I * R
T = W * Rth

https://en.wikipedia.org/wiki/Thermal_resistance

 

[2 picoDumbs]

I know this is an old thread but i also find this confusing.
Maybe someone could explain a little further.

Most likely a simple mistake

 

[Nelson Pass]

Yes, should have been +25, and old calculator.

(me)

 

[Zen Mod]

yup

but even with + instead of - , it can't be 116

however , what's small typo between friends ....... logic is what counts

 

[Gyuri]

Papa just put to the test us.

 

[Zen Mod]

even if flawless - when making amps ,he's deadly serious ..... in same amount as Kung Fu Panda



however , when numbers and words are in case , ya better read between the lines

 

[Zen Mod]

I found Da Logic :

Tj = W * (Rj + Rc + Rh) + Ta
Tj = 16 * (1 + 1 + 2) + 25
Tj = 16 * 4 + 25
Tj = 64 + 25
Tj = 89

now , just add 42

so

Tj= 89+42
Tj= 116

 

[2 picoDumbs]

Ok lets do this for a tough as nails SiC Mosfet. (Tj = 200 deg)
SCT30N120 http://www2.st.com/content/ccc/reso...df/jcr:content/translations/en.DM00053079.pdf

Tj for SCT30N120 = 200 Deg C
Heatsink Temp = 55 deg C

Ok what is the max power we can hit that baby with if Heatsink temp is 55 deg C

Tj = Watts X (Rj + Rc ) + Th
(According to the data sheet Rj = 0.65 but I'm using 1)

200 = Watt x (1+1) + 55

145 = Watt x (2)

Watts = 145/2

Max Watts at 55 degree Heatsink Temp =72.5W Baaaad SiC Baaaad Hahahaha

Don't assume I got this right. This was more of an exercise to prove how dumb I am.

 

[nigelwright7557]

I have always been a fan of low bias.
Most Peavey amps use this too.

When working out dissipation in output transistors worst case is signal peaking at 2/3 B+.
This is where power dissipation in output transistors is worst case.

A point not to forget is output transistors in class AB are only on for half the time due to the signal being AC.

I can get 150WRMS out of irfp240/9240 pair with a decent heat sink.

 

[2 picoDumbs]

I have always been a fan of low bias.
Most Peavey amps use this too.

When working out dissipation in output transistors worst case is signal peaking at 2/3 B+.
This is where power dissipation in output transistors is worst case.

A point not to forget is output transistors in class AB are only on for half the time due to the signal being AC.

I can get 150WRMS out of irfp240/9240 pair with a decent heat sink.

I don't really build class AB anymore.
I usually have my amps dissipating a constant 200W of Class A power. That's generally the size of heatsinks I use.
I'm in the middle of building a beast though, that one will be 380W

 

[nigelwright7557]

I don't really build class AB anymore.
I usually have my amps dissipating a constant 200W of Class A power. That's generally the size of heatsinks I use.
I'm in the middle of building a beast though, that one will be 380W

So you are the one responsible for global warming ?

I have always built class AB or class d.
But my uses are for mobile disco and guitar so power and efficiency is important.

 

[2 picoDumbs]

Yeah. I'm trying to prevent the next ice age from occuring.

 

[2 picoDumbs]

So you are the one responsible for global warming ?

I have always built class AB or class d.
But my uses are for mobile disco and guitar so power and efficiency is important.

For Bass Guitar, I'd build a 400W Class AB amp.
Tube at input with push pull lateral mosfet source follower at output.

 

[Sangram]

So you are the one responsible for global warming ?

I can bet anything you like that the excess carbon dioxide from 200 dancers at a disco will contribute much, much more to global warming than one guy sitting for a few hours in the evening in front of a Class A amplifier.

And if you add the strobe lights, airconditioning, drinks refrigerator and the vehicle emissions involved in getting to the disco and back - well, then it would be more than every single Pass Labs Amp ever produced, if all were operated together for exactly the same amount of time as that disco.

 

[2 picoDumbs]

I don't have a 3kW air conditioning unit that runs 10 hours a day (70 hrs a week).
So I guess 300W for 2hrs a week listening to some music is a lot less than the person using a 3000W airconditioning unit for 70hrs a week.

I need to get me one of those air conditioning units. My plants like the CO2. Don't want to starve those poor innocent life forms.

 

[el_mariachi]

I found Da Logic :

Tj = W * (Rj + Rc + Rh) + Ta
Tj = 16 * (1 + 1 + 2) + 25
Tj = 16 * 4 + 25
Tj = 64 + 25
Tj = 89

now , just add 42

so

Tj= 89+42
Tj= 116

I'm not less confused after that

So how about this:

W = 116 - 25 / (1 + 1 + 2)
W = 91 / 4
W = 22,75

Each device dissipating 22,75 W
12 devices = 270 W

Lets say an Aleph 2 has 12 devices dissipating about 200 watts, or about
16 watts each.

However the user manual states that:

The amplifier draws 300 watts from the wall at all times, and during idle operation nearly all of
this energy will appear as heat on the heat sinks.

So if my "dumbmeter" is past the full scale of one hundred right now please......................

 

[2 picoDumbs]

(89-25)/4 = 16
12 × 16 = 192W


Zen Mod was being a funny man. 42 is the answer to life, the universe, and everything.