Motor Controller...

[ILikeComputers]

Hi,, my friend and I are working on this project and are going to make the board soon. Just wanted to see if any of you could spot any problems in my schematic.
Thanks

 

[cr0sh]

I'm pretty sure that h-bridge design won't work - or only poorly at that; those are all n-channel mosfets (non-logic level), and I don't see where you are providing high-side turn-on; not to mention that they won't switch on fully at 5 volts (logic level from the ATMega)...?

 

[ILikeComputers]

So, I need to add transistors for switching the Mosfets on with 12v? Anything else?

 

[4pyros]

P-channel mosfets for switching the high side voltage.

 

[ILikeComputers]

Like this?

 

[cr0sh]

So, I need to add transistors for switching the Mosfets on with 12v? Anything else?

First off, I am not an expert on h-bridge design, whether mosfet or transistor-based, so take this with a grain of salt, listen to others who are, and do more research...

1) As 4pyros has noted, your high-side should be p-channels to switch the high-side voltage
2) Alternatively, you can do an all n-channel design, but you will need to use a high-side driver - either an IC designed for this purpose, or a charge-pump design
3) Note that charge pumps (and I believe some IC drivers?) generally need to always have a PWM signal; you can't just switch the mosfets "on" - the PWM keeps the pump "primed" so to speak; there are also limitations on speed of PWM, etc - based on the design and/or parts used.
4) If you aren't using logic-level mosfets for whatever reason, then yes, you can use a transistor to switch them instead (typically you would use the input voltage rail of the h-bridge; 10 volts or greater, whatever is being used to supply the motor)
5) Select mosfets of an amperage 3-4 times larger than what the motor is rated for (and/or parallel the mosfets if needed to get this level)
6) Remember to use heatsinks if needed

Once again - I am not an expert on this; this is all just from what I have researched on the internet in my own study of high-power h-bridges; in the end, I decided that if I ever needed anything over 10 or 15 amps, it was going to likely be better and cheaper to just purchase such an h-bridge...

Good luck - hope this helps!

 

[ILikeComputers]

Thanks so much for the help, I going to rework and then repost tomorrow.

 

[ILikeComputers]

I have been nice and busy... so here is what I have.

I would also like to know if these mosfets will work. I checked the datasheet, and I think they have a fast enough switching rate, but would not mind if some double checked

https://www.electro-tech-online.com/custompdfs/2011/11/CD00002632.pdf

Its to TO-220

Thanks you so much for the help!

 

[KeepItSimpleStupid]

Why is C6 440 uf? Look at the datasheet for the regulator. 1000 uf/amp is a good size for the inout side of the regulator.
Think of it this way: The voltage across a capacitor can't change instantaneously. A regulator is supposed to keep the voltage constant. It's like two brick walls fighting each other. Caps on the output are usually used for stability and transients. Regulating the voltage across a capacitor is counter-intuative.

The direction switch is kind out in left field.

Generally it's not a good idea to use the power supply as a reference unless you need it for ratiometric purposes. A buffered real reference IC is the preferred method. I'd at least leave room for a small cap to ground on your speed control pin. It would help minimize transients from the wiper while moving the pot.

 

[4pyros]

I have been nice and busy... so here is what I have.

I would also like to know if these mosfets will work. I checked the datasheet, and I think they have a fast enough switching rate, but would not mind if some double checked

https://www.electro-tech-online.com/custompdfs/2011/11/CD00002632-1.pdf

Its to TO-220

Thanks you so much for the help!

Those are n channel you need p channel too!!

As 4pyros has noted, your high-side should be p-channels to switch the high-side voltage

 

[ILikeComputers]

Thanks for the response, but I am just a little confused. Those are P-Channel mosfets...
What change do i need to make? from what I understand, I need N-channel for the mosfets that connect to GND...
Thanks

 

[4pyros]

Thanks for the response, but I am just a little confused. Those are P-Channel mosfets...
What change do i need to make? from what I understand, I need N-channel for the mosfets that connect to GND...
Thanks

OK sorry, looking back all the mosfets you spec'ed are P channel and will work for the high side. Now you need two n channels fets for the low side and change your drawing.

 

[ILikeComputers]

Thanks so much for the help!
Here is the N-Channel mosfet I decided on:
https://www.electro-tech-online.com/custompdfs/2011/11/CD00001997.pdf

I added that to the schematic and increased the number of smoothing caps on the output.
Thanks!