Continue to Site

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.

  • 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.

High Current H-bridge circuit using mosfets

Status
Not open for further replies.

Damnusername

New Member
Hello everyone
I have made an H-bridge circuit using p-type Mosfets (IRF9540) and n-type mosfets (IRF540). My circuit works fine in one direction and drives motors with a reasonable RPM but on reversing the direction, RPM sufficiently decreases to a point where motor is almost not working, mosfets and wires start to heat up. Sparking on battery terminals is also observed.

I m using two BJTS ( C546 and C556B) along with a single optoisolator( 4n25) to drive each mosfet. There are four such units in my h-bridge

Please help me out with this
 
We can't help you with anything if you don't post a complete schematic of your h-bridge circuit.
 
You are using P and N mosfets in the same H-bridge? Shouldn't they all be the same type, preferrably n-type using a positive voltage rail?
 
No smatches, the low side of the h-bridge are driven by N fets, and the high side is driven by P fets. You can use all N fet's but the gate voltages for the high side fets need to be isolated or the circuit doesn't work.
 
Oh, ok. I've been working off just one H-bridge design, which is all Nfets with a floating "common" between the high and low side. Everything is isolated.

This is actually the class info that most of my information has come from (No, I'm not going to school.) It was one of the only sources that showed how to do it practically. Too much theory on the web, not enough practical examples.

**broken link removed**
 
For h-bridges? You haven't looked enough!
What are you doing for isolation for your Nfets?
 
All the firing circuits are isolated using logic level optoisolaters. I was using the class suggestion and trying transistor outputs, but trying to work within the linear range was not ideal. Changed to logic level and everything is much cleaner.

Small 12v power transformers isolate the low voltage rails from the mains. This isolates the LV rails from the mains on both the controller and power sides.

I have not buitl a schematic for it yet. Will do that shortly.
 
opto isolaters aren't as effcient as a good direct drive. Optos have pretty 'course' turn on and off times.
 
I really wanted the safety of them though, as tht PIC that I'm using for the PFC/H-Bridge needs to talk to the MCP (Master Control Pic :)) which is also talking to a number of other small modules. Also just like to push the safety envelope for the sake of practice/learning.

Here are the logic opto's I'm using. They are quite nice and don't inject too much delay into the firing circuit. And now my minimum PWM width is 50ns, instead of 500ns which was the best I could get using the transistor outputs.

https://www.electro-tech-online.com/custompdfs/2009/03/6n137vo2.pdf

Just realized we hijacked this thread. OP, post a schematic. :p
 
Watch your frequency, optos's have pretty soft on/off limits. If you increase the frequency too much the opto forces the FET's into their linear range and they self destruct.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top