denci

As we know power dissipation of one of three 2N3055 output transistor is aprox. 65W and recommended thermal resistance for heatsink for one transistor is (200-35)/65 - (1.5 + 0.2) = 0,84 °C/W, but how can i calculate the required thermal resistance of heatsnik for three same transistor with the same power dissipation? Is ther any equation for this or is eought that i get the heatsnik with thermal resistance three times smaller than thermal resistance for one of each used transistor??...sorry for my english!! TNX

Where should i place the 1kohm pot3 for fine voltage regulation?

Tnx a lot!

What is wrong with my heatsink calculation in 5 post ago??

http://www.changpuak.ch/electronics/calc_23.php With this online claculator i have got the same results ??? ???

I usually use this way to calculate the heatsink, it is wrong that way: (130°C-30°C)/4.5W - (10C/W+0.3C/W) = 11,9°C/W

So, what heatsink do you suggest, how much should be a thermal resistance, i have one heatsink with 5°C/W at home, which I intend to fix on housing of BD139. I think that it is enought for condition in this stabilized power supply with max 5A current or not??

I calculated the heatsink wit aprox. 0.5°C/W thermal resistance for one transistor, how much must be that for three 2n3055. What fun you suggest?? what dimension and voltage?

So, this is my first post on this forum, first hi everybody!! ;D I will make this project in near future therfore i am interested how to calculate total dissipation on transistor 2n3055. I will use the 5A (REV3) version of this project, so i'll use three transistor and transformer 30VAC 210VA. I need this calculation for calculate heatsink thermal resistance for three paralleled 2n3055. Is this calculation is correct or not: Pd = 5A * (40V - 0,55V - 1.35V) = 190,5W i got 0,55 from total voltage drop of three 0,33ohm paralled resistor (0,11*5), 1.35 is voltage drop on shunt resistence R7 (0,27ohm*5A)