Parallel Transistors?

[George]

But still - are FETs as easy to control in a current regulation situation? Also - are there many that can dissipate over 100W of power? I've never used a FET before to limit current and am not really sure how easy it would be to get a good steady current regulation from one.

I was thinking - what if I use a length of copper wire say 0.1 Ohm from each of the emmiters, the copper would naturally increase it's resistance as it gets hot and let less power through the transistor - so then it would have a semi dynamic leveling system rather than just a static resistor?

[wjsmarine]

Hi George, members.

Mosfets are capable of big power, no problem, obviously heat sinking is a factor. I would be careful using pcb tracks as a resistor where you are relying on heat as an aid in resistance changing - there is a fine line (no pun intended) between getting hot enough and a fuse, but if you decide to do this see Roman Black's site
http://www.romanblack.com/pcbtemp.htm
for a utility to allow calculating track sizes.

I have had good success with an arrangement that controls Source current by robbing Gate drive. Use a Source resistor (N channel device) to ground and place the b-e junction of an NPN bipolar across it. The collector goes to Gate with a 1k. This will rapidly switch so the average Source current is controlled by the Source resistor - value determined by 0.65/desired current e.g. 0.065 ohms will give 10amps average.

If this meets your needs I would start small and scale up accordingly.

I hope this helps.

Regards,
Bill