MOSFET driver revised

A project log for DC Motor Controller for CNC Router

DC motor rotational speed controller for Chinese CNC3040 spindle motor without any kind of encoder

SUFSUF 04/25/2015 at 21:362 Comments

I was thinking, looking around a lot before I designed and built the current motor driver circuit. I wanted to use something cheep, something I can learn from.

The current one is working, but I was thinking, how can I make it a little bit faster. When I designed the current one, experimented lot on the breadboard, but not used ltspice to simulate the circuit. When it was finished, I needed to tweak it, here and there, to be able to reduce the noise for the clear measurement signal.

Now I'm trying to get faster switching, to reduce the heat generated by the MOSFET.

First of all I run a simulation of the original circuit.

The circuit:

And the result:

As you can see the the timing results:

Switch on time: ~500ns

Switch off time: ~500ns

After 2-3 weeks of continuous (in my spare time, what I not really have to much) simulation, changing components, pursuing different ideas, finally I created a little bit better one.

The circuit:

And the result:

And the timing:

Switch on time: ~30ns

Switch off time: ~100ns

Much better.

Based on the things above, I designed a little bit different circuit. The reason: I use mostly trough hole components for the home made PCB and switch to SMD when I order the final one.

The schematic

And the PCB design:

Hopefully I'll be to build it during the weekend.


jbb wrote 06/05/2015 at 21:33 point

Hi Suf

Welcome to the interesting world of power electronics, where all those pesky nanoseconds matter :-)

I'm curious - your PWM_IN connector J2 has 2 inputs.  How are these driven?

Additionally, I noticed that you have a little bit of a challenge in the gate drive design: you've used 33V Zeners and the 48V supply rail to provide the -15V Vgs for driving Q4. What happens when the supply is not 48V?

Finally, if you have trouble with D4 getting hot you could move to a synchronous rectification platform (i.e. put a MOSFET where diode D4 is).


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SUF wrote 06/05/2015 at 22:06 point

Hi jbb,

The two inputs just connected to a single MCU pin for now. I just wanted to keep the opportunity to tweak the switch on and switch off times. Future improvement maybe. :-)

About the Zener. The circuit will be driven from a 48V SMPS, so the 48V is a stabilized input. If I've problem with it, I'll redesign it.

You quite right about the synchronous rectification, I just didn't wanted to complicate the circuit further, or use some drop in integrated controller. If I'll have problem with it, I'll go with a Linear Technology's half bridge controller, what has a boost converter instead of a bootstrap capacitor, to be able achieve 100% duty cycle, and using N Channel MOSFETS.


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