Whats the best way to drive a power mosfet from a uC PWM signal?

Thread Starter

Subterranean

Joined Jul 27, 2010
13
This seems a fairly simple topic but I couldn't find a comparative view anywhere so I apologise if its a simple answer.

I am looking to drive a couple of power mosfets in parallel (probably IRFP2907) from a PIC microcontroller. I realise that the mosfets need at least 10v to fully turn on so I will probably use a 12v rail that I'm already planning to have in the project.

What is the best method to drive the power MOSFETS from the microcontroller's 5v output? I have thought of 3 different options but I'm not sure if any of them are immediately the obvious choice:

1. Use a smaller MOSFET that turns fully on at 5v to supply the 12v to the power MOSFET gates.

2. As above but use an op-amp.

3. Use a mosfet driver IC.

I would have thought option 3 would be the best, given that it sounds like a mosfet driver is designed to do exactly what I'm looking for, except that I can't find any noob friendly information about how they work and how I would integrate one between a uC and a power mosfet. If anyone can help with this please do.

The first two options seem simple enough, but perhaps I would struggle with controlling the gate capacitance of the power mosfet?

Any help would be very appreciated.
 

jpanhalt

Joined Jan 18, 2008
11,088
A dedicated driver is probably your best bet. There are lots of options. Look up MC34151/ MC33151 as an example. The datasheet has several pages on layout and operation. It will take logic input.

John
 

retched

Joined Dec 5, 2009
5,208
You can get power MOSFETS that have LOGIC level gates (5v)

For speed, you will want to use a gate driver.

I like these:

Clare IDXF604

Logic input. 10nS rise times.

It depends also, if you are doing high or lowside switching.
 
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Thread Starter

Subterranean

Joined Jul 27, 2010
13
Thanks for the info on mosfet drivers, it sounds like I will use one of those.

But theres still one simple thing I don't understand, how would using the mosfets in a high or low side configuration make a difference to how the driver needs to operate? Since you can get high and low side drivers I assume it does matter but I dont see how the drivers themselves would be different for the different switching methods. Or is it a bit complicated.

Thanks again.
 

shortbus

Joined Sep 30, 2009
8,322
Thanks for the info on mosfet drivers, it sounds like I will use one of those.

But theres still one simple thing I don't understand, how would using the mosfets in a high or low side configuration make a difference to how the driver needs to operate? Since you can get high and low side drivers I assume it does matter but I dont see how the drivers themselves would be different for the different switching methods. Or is it a bit complicated.

Thanks again.
With a high side mosfet you need to bring the gate voltage up to 10V higher than the source voltage. The driver and a few other components let you do this.

With a low side mosfet you just need the gate voltage to be 10V, because the source is at '0'V or circuit ground.

You probably already know what makes a mosfet high or low sided, but if not this is the difference ---
High side - the load is after the mosfet, between mosfet source and "ground'.
Low side - the load is between the positive voltage point and the drain of the mosfet.
 
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