MOSFETS for H-Bridge

[francisjoe45]

Hi, it is my first time to design a motor controller for a BLDC motor and I am confused on what kind of MOSFETS to use. I would like to drive the MOSFETs using a PIC microcontroller, (dsPIC33F).

Let's say an H-bridge for example, where there is High-side and Low-Side driving, should I use a pair of P-Channel and N-Channel MOSFETs for the half bridges or can I use 4 N-Channel MOSFETs instead? I am very confused since the gate of P-Channel MOSFETs, as I understand, needs to be supplied with a negative voltage for the FET to turn on.

[sacherjj]

Here is a decent article that might help.   http://www.modularcircuits.com/h-bridge_secrets1.htm

N Channel just generally perform better, but are a little harder to use on the high side.  That article discussed some of the challenges.

[Neilm]

N Channel just generally perform better, but are a little harder to use on the high side.  That article discussed some of the challenges.

There are chips available that will take the the work out of driving either half or full H-bridges (for instance NCP5304 first one I found).  All the user has to do is provide the drive signals. Some of the chips available will also provide shoot through protection.

Neil

[mkissin]

Yeah, I'd definately go with four N-channel FETs.

How easy or hard they are to drive will depend on your DC bus voltage. Up to about 600V, things are pretty easy, as you can get heaps of half-bridge driver chips with inbuilt bootstrap power supplies to drive the high side FETs. Personally, I usually use the ones from International Rectifier (like the IR2104), but there are plenty of others.

The half-bridge drivers generaly have built-in dead time to avoid shoot-through faults (although they often don't have shoot-through detection. That's another issue), and the bootstrap supply is simply a diode and a capacitor.

Above 600V things are trickier, but unless you into really high power stuff that's not such an issue.

[Zero999]

For higher voltages (above around 400V) IBGTs start to become more efficient than MOSFETs.