HomeMade Motor Controllers

[John Gutmann]

Originally Posted by sciguy125

http://en.wikipedia.org/wiki/Field_effect_transistor

A MOSFET is a kind of FET. I'm not well versed in transistor theory, so I'm not sure what you gain my using other FETs over MOSFETS. But the reason MOSFETs are used as opposed to normal bipolar transistors is that you can parallel them. Let's say I have a MOSFET and a bipolar that can handle 10A each. For my device to handle 50A, I would need to parallel 5 of them. Paralleling the MOSFETs is fine becuase when they heat up, their resistance increases. Let's say that MOSFET 1 starts to heat up. Its resistance increases and it carries less current. The other 4 would pick up the slack. As 1 starts to cool down, it will carry more current and another would get a break. Of course, it isn't that linear and it happens very fast, but I think it gives you the idea. Bipolars, on the other hand, will all heat up together. When one of them finally explodes, the others are left with distributing the full 50A load and another will blow even faster than the first one. They will all cascade until you have nothing left but a smoking pile of transistors.

so a MOSFET is like the same thing but only, i guess you would say safer?