HomeMade Motor Controllers

[Adam Y.]

That's why the Victors can handle such a high current. However, it gets very dangerous to handle such a high current.

Well in reality the only danger that you have at such low voltages is from stuff exploding. You really can't be harmed from shock but even at 36 volts the amount of shrapnel produced by the FETs is amazing when they fail.

Not exactly, MOSFETs and bipolars each have their uses. They work in slightly differnet ways that would suite different applications. In some applications, you would need to use bipolars because MOSFETs won't work and vice versa. For a high powered motor controller, I think the MOSFETs would be best.

Your forgetting about IGBTs which is an odd mix between an MOSFET and a BJT. Essentially, it turns on like a MOSFET but handles current like a BJT. Also Power MOSFETs are different from regular MOSFETs because there is a diode included . If you look at a circuit symbol for a power MOSFET you will see that diode include.

There is a helpful guide on the IRF website that explains how to pick your MOSFET and match it with a proper MOS Driver. Its really complicated...

It's complicated to the point where I really wouldn't recommend such a project if your not out of in college. If your PWM frequency is high enough you may run into transmission line problems. You start running into weird parasitic capacitances/resistances/inductances that cause the gates to ring which will result in the FETs not turning on and off cleanly. The high side drivers can actually latch on which results in the FETs staying on when they shouldn't be. I spent the last four months with people much smarter than myself trying to do essentially what you want to do but we really had problems.

[sciguy125]

Originally Posted by Adam Y.

Also Power MOSFETs are different from regular MOSFETs because there is a diode included . If you look at a circuit symbol for a power MOSFET you will see that diode include.

I'm sure that power MOSFETs do have some differences in construction, but that diode is in all MOSFETs; it's part of the way they're built. This diode is called a parasitic because it exists, but isn't there intentionally. Attached is a drawing of a MOSFET with the parasitic diode in red. Note that the diode only exists when the source and body are connected (as it usually is).