Low voltage H bridge

[Navarr0]

Hello, please, I need help. I have MCU with LED display, both powered from two AA batteries with DC 5V converter. Now I need control little DC motor (1.5-3V and current max 500mA). So I wanna build H bridge controled with 5V voltage from MCU. Can you tell me, if this circuit will work? https://www.electro-tech-online.com/imgcache/3304-idea.JPG. H bridge must be powered directly from two AA (cca 3.2V when new). I wanna use four n-channel mosfet TSM2302CX with Vgs(th)=0.95V. For low side nfet there is Vgs=5V without problem. But for high side nfet there is 5V-3.2V when open =1.8V, so it's still good? Thanks for response.

 

[barry]

Maybe it will work. You have to make sure your Vgs on the top mosfet is large enough to turn it on sufficiently. Looking at the data sheet, it appears it might work, but personally I'd use a more robust gate drive on the top. It depends on whether this a product you're going sell tens of thousands of, or just a hobby project. I would also look at "logic-level" MOSFETs which have an intentionally low Vgs on voltage.

 

[Navarr0]

Hello, thank you for reply. It's only for my hobby project. I willl use for high side PFET TSM2301CX, which has also low Vth=0.95V. FETs which I want to use have lower threshold voltage than every logic fet I can get. So I hope, it'll work.

 

[doraemon]

Hello!
Why bothering with discrete components? At that power range, you have myriads of chips that will make it.
I have made a board that uses that kind of integrated components, and it works just fine.
The motors voltage is 3 to 7.2V, the processor 3.3.

Have a look here:
https://www.youtube.com/watch?v=szZOTKKYvnU

Best regards

Pascal

 

[barry]

Don't get confused by the Vth spec. That's just the point where the device JUST STARTS to conduct; it's not where you want to operate.

 

[Audioguru]

1) The threshold Vgs voltage of a Mosfet is when it is barely turned on and conducting a low current (0.25mA). Do you want the motor to be barely turned on and conducting a low current?
2) Your upper N-channel Mosfet needs to have its source turned on to +3V then its gate voltage must be much higher than +3V.
The circuit might work if the Mosfets have a typical or better threshold voltage. Then you need luck.