• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

PWM Driven H-Bridge

Status
Not open for further replies.

jrudd

New Member
I'm working on a dual h-bridge design and I have a question concerning delivering the PWM signal. I'll be using N-Channel Mosfets on the high and low side and a PIC to create the PWM signal.
My rudimentary thinking(non EE) says I should send the PWM to either of the high side mosfets, depending on the direction that I want to go, while turning on, and leaving on the opposite low side.
However, a lot of schematics and data sheet app notes for gate drivers I've looked at, indicates that the PWM signal is sent to both high side and opposite low side with one being inverted.
Can I drive the bridge the way I'm thinking or is there a down side, such as decreased eff or something.
Thanks,
John
 

Mr RB

Well-Known Member
You may get better efficiency driving PWM to the low side as NFETs are usually easier to drive that way with a good clean high current signal (to overcome the gate capacitance). Leaving the opposite high side turned on is standard and allows a freewheeling path for the motor current in the off cycle.
 

Speakerguy

Active Member
Both sides of the bridge need to be switched to charge the bootstrap capacitors for the high side gate drive capacitors. Hence switching the entire circuit from conduction in one direction to conduction in the other direction. Trust me, I found this out the hard way.
 

jrudd

New Member
Mr RB

I have attached my 1st pass schematic below. It sounds like what you are saying is that I could run my PWM signals to the low side only while just switching the high side on and off depending on direction. Essentially reverse of that shown on the schematic. Is that right.
 

Attachments

Mr RB

Well-Known Member
Yes you can PWM one side only. Of course like speakerguy said you need to have a way to drive the gate voltages of the high side, which preferably should have their own psu voltage rail.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top