H-Bridge motor control confusion....

[[email protected]]

I'm trying to build an H-bridge circuit to control a 12V DC, 2.5A motor

from the DAC (0v~5v) output of an Atmel micro controller. I've looked
at lots of designs of h-bridge, even tried doing some examples in
Crocodile Technology. But things just don`t seem to work...

Can anyone help... open to any suggestions. I`m not thinking of trying

a L298, but not 100% convinced!

 

[Chris]

I'm trying to build an H-bridge circuit to control a 12V DC, 2.5A motor

from the DAC (0v~5v) output of an Atmel micro controller. I've looked
at lots of designs of h-bridge, even tried doing some examples in
Crocodile Technology. But things just don`t seem to work...

Can anyone help... open to any suggestions. I`m not thinking of trying

a L298, but not 100% convinced!

There's another thread going on where the OP (Michael) had started out
with this circuit. It looks like it would be a good fit for your
application:

http://www.cadvision.com/blanchas/hexfet/np-s.pdf

Note that this circuit expects 12V logic signals -- you'll have to
convert from the +5V logic signals of your microcontroller.

Good luck
Chris

 

[BobG]

============================================
I'm intimately familiar with several models of Atmel mega AVR
processor. Can you tell me which version you are using that has a D/A
converter?

 

[John Fields]

I'm trying to build an H-bridge circuit to control a 12V DC, 2.5A motor

from the DAC (0v~5v) output of an Atmel micro controller. I've looked
at lots of designs of h-bridge, even tried doing some examples in
Crocodile Technology. But things just don`t seem to work...

Can anyone help... open to any suggestions. I`m not thinking of trying

a L298, but not 100% convinced!

---
H bridges aren't usually designed to drive a motor linearly, but
rather via Pulse Width Modulation (PWM).

The reason for that is if the motor were driven linearly its torque
would diminish as its speed decreased, and the power wasted in the
drivers would cause them to heat up much more than necessary.

Using PWM, the drivers are always either in transition or all the
way on or all the way off, so the only power they dissipate is
Vce(sat) * Ic for a bipolar transistor or Rds(on) * Id^2 for a
MOSFET, plus whatever gets dissipated while they're switching.

 

[[email protected]]

Thanks for the repsonses...

So, it sounds like it would be better for me to change to PWM as a
control method. So thats my next question, how? I`m getting an
analogue voltage from my Atmel Mega32 from 0v to 5v, depending on an
input from a PC. I have seen a few PWM circuits, using 555 timers
etc...

Anyone care to guide me in the right direction for this?

Appreciate everyones help.