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Topic: Tired of Burning up Transistors...Need an H-bridge (Read 4425 times) previous topic - next topic

coolshawn92

I have look throughout the internet and have developed an H-Bridge using MOSFET transistors (IRFIZ44NPBF N-channel) (IRF4905PBF P-channel), but smoking keeps happening as the transisitors get hot and burn up.

I am running out of time and I am stress. I would like to just easily use an H-bridge with built in flyback diodes for ease of use to control my 24 V, 350 W motor.

Most of the INEXPENSIVE H-bridges that I have seen online are for low current.

Does anyone know where I can locate a High Current capacity H-bridge that is inexpensive?

Thank you,
Shawn

coolshawn92

I had no diodes across my transistors assume they had build in flyback diodes, but I do not even know if that was the problem. The circuit seem to be connected correctly as it would run for a little while then stop.

The circuit was just simply 2 PNP up top and 2 NPN transistors on the bottom. I figured this would do the job, but I was wrong..

RuggedCircuits

Whoa there...you're mixing the words "MOSFET" and "NPN/PNP". Not the same thing at all...."NPN/PNP" suggest bipolar transistors (BJT's) and not MOSFET's. But the part numbers you listed (IRFIZ44NPBF and IRF4905PBF) are indeed MOSFET's.

Do you have a schematic you can show us?

A 24V 350W motor suggests about 350/24=14.5A of current, right? The IRFIZ44NPBF has an Rds(on) worst-case of 24mohms, which will dissipate about 5W of heat at 14.5A. That's too hot for this device without some aggressive heatsinking or forced-air cooling. It is not surprising that your transistors are smoking/burn up. You need to find MOSFET's with lower Rds(on) values (and also show us the schematic to make sure you've got everything hooked up right :) )

You could always use a high-current motor driver module like this:

http://www.pololu.com/catalog/product/1455

I'm not sure you're going to get much less expensive for that kind of power level.

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keeper63

High current h-bridge and "inexpensive" do not belong in the same sentence...

BTW - how were you switching on the MOSFETs? What voltage on the gate were you using? > 10 VDC? Did you have them mounted on heatsinks?

What are the current ratings for the motor (running and stalled)?

Both of those devices have built in protection diodes, but external diodes don't hurt things, either. Without having some more information, my initial guess is that you weren't turning the MOSFETs fully "on"...
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

zoomkat

Quote
The circuit was just simply 2 PNP up top and 2 NPN transistors on the bottom. I figured this would do the job, but I was wrong..


Did you use a ~proven design, or just wire something up? Not knowing what you call expensive, the below h-bridge is probably the least expensive I've seen for large loads.

http://secure.oatleyelectronics.com//product_info.php?cPath=94&products_id=206&osCsid=30093449b694ae247d94c2bcce5d0560

http://secure.oatleyelectronics.com//product_info.php?cPath=94&products_id=827&osCsid=30093449b694ae247d94c2bcce5d0560
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coolshawn92



HERE is a very very very rough sketch of what it looked like done in Paint.


coolshawn92

I guess I do not know how to insert an image.

coolshawn92

ZoomKat,

On the links you listed, do you know if I will be able to connect the boards to the arduino Uno. I am looking at the specs, but they just mention a switch?

bld

"http://c/Documents%20and%20Settings/shawn.oates/Desktop/untitled"

You linked to it, on your own harddrive.

You need to use a picture upload service. :)
captain-slow.dk | non contagious!


gardner

If you could drop the voltage to < 20 there are some good IC motor controllers that you might be able to use.  ST's VNH2SP30 is available in some ready-made driver circuits that could save you some trouble.  15V and 15A seems readily doable.

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