PWM question

[ifsercon]

I have a 3.2A 2.56v stepper .
If I put a 10% 100KHz 25.6v PWM power on a coil the voltage
will be 2.56v and the current 3.2A or I burn the coil ?

[RomanLini]

You need to measure the current, and control it. You can't rely on a voltage:current ratio as the motor is both inductive and reactive.

All good motor drivers maintain a fixed coil current, the voltage can be whatever.

[ifsercon]

Hi
What a coincidence !

Just wanted to test your high torque half stepping !
100% + 40% mode!

Tested it but speed is small.
Thought to put a 10% and a 4% PWM from a 10 times greater supply then stepper's plate voltage.
Without current control...
With 75-100 KHz PWM would the current raise to much ?
With my cheap DMM I get erratic current readings.
I'll get one analog amper-meter in next weekend from a friend.

Sorry for my english...
F

[RomanLini]

Sorry there's no easy way around.

You can use resistors to drop the voltage and counter the coil inductance, many early stepper drives used a higher voltage and 4 resistors for the 4 motor coils. It works ok but the resistors get hot.

A much better approach is to control the current using linear current feedback, it's the best performance but the transistors still get hot.

Or you can use chopper controlled current feedback, it runs more efficiently and fairly cool and works almost as good as linear current control. And it's often cheaper. Check out any of the datasheets for "chopper stepper motor driver IC". It may give you some ideas you can use in your design for current control.