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STEPPER MOTORS (part 2)

Now lets take a look at the main 2 kinds of stepper motors.
Unipolar motors and bipolar motors

Unipolar motors have in general 5 or 6 wires that connect to the windings. The advantage of this type of motor is that it can be driven by four transistors on ground reference(no high side transistor drive).
Always the center wire is connected to the plus source.
This is easier than controlling 8 transistors in a bridge.
The sequence to rotate the motor here is easy. Lets consider the notation 1a for the case where current flows from terminal one to terminal a.

--->--->--->--->--->--- (Ratation direction)
1a - 1b - 2a - 2b - 1a .... (Winding sequence)

---<---<---<---<---<--- (Ratation direction)
1a - 2b - 1b - 2a - 1a .... (Winding sequence)


Bipolar motors have a 4 wires instead that connect to the windings. To drive the motor you need an H-Bridge to be able to let the current flow on both directions in the windings. The sequence to rotate in one direction or the other is simple. Lets consider the notation 1ba for the case where current flows from 1b to 1a as shown with the arrow.
>---->---->---->---->---->
1ba - 2ba - 1ab - 2ab - 1ba .....

<---<---<---<---<---<---<---<
1ba - 2ab - 1ab - 2ba - 1ba ....

Having in mind this basic concept of stepper motors here is a simple circuit from ST semiconductors that offers some nice features like a chopper operation, half step, full step and a disable/enable option.

This circuits is based on the ics from ST L297 and L298.
Here is the circuit, but i suggest taking a look at the data sheet of this 2 ics for more detailed information. I'm working on a board with this circuit that I will sell completely assembled and tested for those who do not have the time or the tools to build it.

 

 









 

 

 





Let's look a bit into some more advanced concepts in PAGE3