Please help Bootstrapping MOSFETs in H-Bridge for Arduino (PWM) control.

Other Hardware Motors, Mechanics, Power and CNC
1

Hello!

I am building a heavy duty 3 phase H bridge using only N Channel power MOSFETs

I have bootstrapped the HIGH side FETs according to the schematic that I found on the net.
I use 12v to power the load. This makes the output of the bootstrapping circuit around 24v.
This goes to GATE of the FET.
The control signal is 5v (from Arduino).

Credit for the schematic goes to the original author.

It works pefectly and my N-Channel HIGH side FETs are now fully openable and dont get warm.

I have a problem with the LOW side: FETs get hot very quick.

I would also like to bootstrap the LOW side in exactly the same way.

I have been struggling to modify the above schematic (which is for HIGH side) to be usable on LOW side.

I have been trying different things on breadboard on in LTSpice but with no luck so far.

Could I please have some help bootstrapping the LOW SIDE FETs with a schematic similar to the one above?

I googled around a lot and wasnt able to find anything appropriate. I dont want to use a 555 timing circuit or anything else complicated... Need something very similar to the schematic above, but for LOW side.

Any help and advice would be appreciated.

2

You don't need to bootstrap low-side FET's because the N-channel MOSFET gate voltage is relative to ground, not relative to the motor terminal. You just need to amplify 5V to 12V (and provide a quick burst of current too). I would suggest using a regular high-current MOSFET driver like a TC4426/4427/4428.

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The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons

3

Hello!

Thanks for your reply.

I already tryed boosting GATE drive voltage to 12V for LOW side FETs - they still get hot quick.
I even tryed with active pnp turn off for my FETs aswell.. Still doesnt help.

In this project I can NOT use driver ICs, the driver has to be made out of discrete parts.

Just like the HIGH side driver which is fully working now.

Now, all I need is to have 24V going to LOW side FETs aswell.

Could I please have some help doing that?

Thanks

4

Now, all I need is to have 24V going to LOW side FETs aswell. Could I please have some help doing that?

Have you tried making a single low side NPN MOSFET setup and gotten it to work as in most H-bridges?