I think I know now what my problem is in balancing parallel transistors.I'm getting confused about what values of resistor I need at the emitter and base.Now clearly a 0.1 ohm resister at the emitter is not doing the job of limiting load hogging.I'm burning transistors to much and it sucks .So I need to add a base resistor as well.Since I'm using a well know transistor (the 2n3055) theirs more information on how to calculate the resistors.
My problem is my math is so rusty that I'm not sure if I'm getting this right or even if I'm using the right values from the data sheet.
http://www.onsemi.com/pub/Collateral/2N3055-D.PDF I would like to try to get this working with the components I have ,then make improvements as better ones become available.
Just need to get the Math right!!
These are the parameters I'm working with.
I have 4 amps from the transformer at 40 volts. I would like 4 2N3055's to share the 4 amps (1 amp each).
According to the Active Region Safe Operating Area I should have around 2.5 amps at 40 volts. So that leaves me a little head room .Around 1.5 amps. These are mounted on a fairly descent heat sink.
Now to calculate the base resistor I need the hFE ( I've been using 5)
The Vce is 1.5 (that's the voltage drop across collector and emitter?)
Ic will been 4 amps.
Vb is 40 volts.
It says Vbe is 1.5 or should it be 0.6 -0.7
Now the 2n3055's are being driven by a TIP100. the reason is I need to have that gain (hFE 1000) to limit the draw from a regulator which needs to be around 0.5mAdc.This is explained in the data sheet of the regulator.
https://www.mikrocontroller.net/attachment/160010/mc1466l_tiff.pdf Nominal Design Procedure and Design Considerations : note 10
So that would give me 4amps at the base of the 2N3055's ( probably have that wrong as well)But I figured I'll use the maximum possible assuming the TIP 100 is is full saturation.I know its not good to assume.
Rb=(V-Vbe)/Ib=(40-1.5)/4=154ohms
Now since the transistors are parallel do I need to multiply that value by 4 from each transistor?
I tossed in the schematic as well because when the transistor blows (only one because of the diodes from collector to emitter saved my back side) the voltage adjust potentiometer also blows.At least I'm not cratering the chip.
I can get the darn thing to a little over 2 amps but then every thing goes south. I don't want to wreck another pot because that was one of my favorite one's