My situation is I want to drive a motor that is 3v (possibly 5v if I change it if required), with 6A current!
I cannot find any motor drivers that come close to this, so I am going to create my own H-bridge.
I was thinking that I would just use 2 P-Ch Mosfets, and 2 N-Ch Mosfets rated at ~ 10A.
My problem is that the threshold voltage is 2-4V for full saturation, so even driving the N-Ch to 3V and the P-Ch to Gnd would not work as they are not getting switch on. I could overcome this on the N-Ch by adding a NPN transistor switch to the actual power source which would be 9V, and driving it to 9V instead then driving the NPN via my PIC 3V supply. But I cannot do the same for the P-Ch as it needs to be minus voltage.
To fix that I was thinking of driving the MOSFETs directly from the 9V power supply, then just voltage dividing the drain outputs of the H-bridge before they reach the motor, but then I am going to lose too much current unless I use a 1 ohm resistor! which is getting a bit silly.
So, other than that I was then beginning to wonder do I even need to use a MOSFET to supply high current, as I originally used MOSFETs to supply the voltage more so than the current, so just naturally thought of them as a driver. But are there better more suited components out there to do this job, or other solutions I am overlooking?
That is pretty much how I am already doing it, using P/N MOSFETs and driving them with NPN/PNP BJTs. That isnt the problem. The problem is the MOSFETs need to provide the motor with 3V 6A, and I cannot saturate the MOSFETS at 3v as their threshold is 4V.
angelsix:
That is pretty much how I am already doing it, using P/N MOSFETs and driving them with NPN/PNP BJTs. That isnt the problem. The problem is the MOSFETs need to provide the motor with 3V 6A, and I cannot saturate the MOSFETS at 3v as their threshold is 4V.
Okay, I can see how that would be a problem. In your original post, you said you could drive the motors at 5v. Wouldn’t solve your problem. You could even PWM the output to keep the current consumption within specs.
Cant limit current through PWM as need all of that current as its driving quite hard. Think the only way around it is a different motor with higher voltage drive (5-15v or something).
Leon, do you mean just use BJT instead of MOSFETs? I was thinking of that as I noticed the 2N2222A had a 0.8A throughput so thought there may be higher rated transistors out there, but not sure whether a BJT is suited for this type of thing as never done much with them?
Since you want to drive the motors at 3V, and you have a 9V supply available, why not use N-channel FETs for the “top” of the H-bridge, as well as the “bottom”?
Use BJT’s to level-shift the output of the micro to drive the “top” FETs in the H-bridge (as well as the “bottom” FETs if you want to improve the on-resistance, or use FETs with a higher Threshold voltage).
I’m just looking at components now. I have a motor that will drive up to .9A as well as the 6A version. Would a BC635 NPN and BC640 PNP be suited for the 0.9A one?