Hi,
As you can see in the picture, this controller is quite rudimentary. The basic unipolar phase sequence is provided by a L297 IC, a marvelous and very versatile chip that every beginner should know about in my opinion as a newbie myself too, and 4 TIP121 darlington transistors are used for the power stage. There is no external resistors or diodes.
As it is, with this 8V, 0.8A motor driven full step at 12 volts and a ballast resistor of 2,4 Ohms I can obtain a G00 speed of 180 RPM with a good usable torque. I don't know the rating but at that speed, I cannot stop it from spinning with my fingers. I can't stop it either at 200 RPM but it is starting to spin a little rough. At 225 RPM I can stop it and at 250 RPM there is about no more torque.
Now for the questions!
With this particular transistor, would it be better to put a resistor between the logic and the base of the transistor. A computer power supply (5V) is feeding the logic part. If needed, what value should have this resistor?
I tried to put external diodes (1N4001) between the collectors and emitters, in the proper polarity, but all I got with this setup was a small humming from the motor with no spinning at all.
What kind of protective diodes should I use and where should I put them. Please indicate if possible the values or numbers.
Ultimately, I would like to use this design with some 2,25V, 2,25A, 70 on. torque recycled Genicom printer motors. I would like to feed them at 12 volts with ballast resistors of around 4,3 Ohms per phase, that is if the ratio is not too much for a 2,25 volts motor. By the way, what is the maximum ratio? I know that it is not the same as the ratio for a chopper board.
Thank you for reading this long post up to here!
Alain
TIP121:
http://www.ortodoxism.ro/datasheets/...onics/4128.pdf