MOSFET H bridge problem: voltage issues?

Other Hardware General Electronics
1

I have assembled a MOSFET h bridge from this design:
http://www.armory.com/~rstevew/Public/Motors/H-Bridges/Blanchard/figure-1.htm

I used the P channel IRF954, and the N channel MOSFETs IRF1405
Data sheets here
http://www.armory.com/~rstevew/Public/Motors/H-Bridges/Blanchard/figure-1.htm
and here
http://www.jaycar.com.au/products_uploaded/zt-2468.pdf

I used 2n3904 transistors to control the mosfets, as specified in the circuit diagram, and I am using +5v from the arduino to turn them on.

On testing the circuit, i found that the motors (6v cordless drill motors) ran slowly or not at all, in some cases heating up and burning out one of the N-channel MOSFETs in the circuit.

The grounds of the arduino and the 6v (yes, I know the diagram says 12v) supply for the motors are ganged together as it doesn't seem to work at all otherwise.

I have found that the device works when the supply for the motors is 12v, AND when the 2n3904 transistors are turned on by the same supply (by touching the signal wires to the battery terminals)

Can anyone please tell me why it doesn't work, why it does work with 12v signal and/or how I can make it work with the 5v arduino signal voltage and either a 12v or 6v supply?

2

Can anyone please tell me why it doesn't work, why it does work with 12v signal and/or how I can make it work with the 5v arduino signal voltage and either a 12v or 6v supply?

Standard mosfets require +10vdc or more to fully switch on adn pass their full rated current, and for applications like H-drive you need the transistors to switch fast to either fully on or fully off. Otherwise the heat dissipation will increase drastically in the mosfets. If you have to run at 6vdc then look for LOGIC LEVEL mosfets of suitable current ratings.

Lefty

3

I don't have to run at 6v, I can run at 12v. What I don't understand is why a 12 volt supply and a 5v signal current wont work.

Could you please explain why a 12v signal worked and 5v did not?

4

The Mosfets NEEDED it to function correctly

5

So what your saying is that there is no way to make this work with the arduino without replacing the MOSFET transistors?

6

there is no way to make this work with the arduino without replacing the MOSFET

Yes.
Or by using transistors to generate a 12V gate signal for the FET.