Driving an N channel Mosfet in a H Bridge on higher side

[Dummy123]

Hi

I am trying to find out how to drive an N channel Mosfet on the high side of a H bridge. The H Bridge drives a stepper motor.

I understand in order to drive the N mosfet in reverse the Gate voltage must be between 4 to 7 V higher than the Supply Voltage. Say the motor voltage is 20 V then the gate voltage must be 24-27 V???? If so, does the gate current also increase compared to driving the N mosfet on the lower side?

If the rest of the board has an additional 12 V and 5V supply for the logic, why can you not only add these to the motor supply voltage and thus obtain the gate drive voltage of +-25V? Why doe you require a charge pump or voltage doubler if this is possible? If this is possible, how do you protect the logic circuit from any back EMF of the motor.

I am a newbee and any help would be highly appreciated.

 

[Analog]

I would recommend reading the PIC micro tips & tricks for DC motor control:

https://www.electro-tech-online.com/custompdfs/2008/03/41233B.pdf

Even if you're not using a PIC, it has a lot of H bridge info in there that will answer the questions you have.

To opt out of the charge pump, why not use a p-channel mosfet on the high side?

 

[Pommie]

If your logic chips have their ground connected to the +20V line and are powered by a 25V supply then they can drive the high side mosfets. Your big problem then is how to turn off your low side fets.

Mike.

 

[Dummy123]

Thanks for the info

The N channel Mosfets are easier and more available. Well at least here in South Africa...

The question regarding the power supply.. I was more concerned with the spikes and back EMF on the logic circuit. Maybe they will damage the MCU?

Actually I found a very good link at
https://www.onsemi.com/pub_link/Collateral/AN1319-D.PDF

 

[ClydeCrashKop]

You might check the Allegro site and general search for bootstrap circuits. It worked well for me and only requires a high speed diode, ~1 mfd cap and an individual opt isolator for each MOSFET.

 

[dknguyen]

Aside from floating supplies (isolated DC converters or boot-straps) and transformer drive, here are non-isolated, non-floating high-side drivers with things like diodes, zeners, capacitors, resistors, and BJTs:
**broken link removed**

 

[Bob Scott]

Check out International Rectifier N channel H Bridge Drivers like this one:

https://www.irf.com/product-info/datasheets/data/irs2011pbf.pdf