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Topic: Transistor Stepper Motor Driver (Read 1 time) previous topic - next topic


I have an EM-257 stepper that id like to run from my UNO but dont want to buy a stepper driver and id like to make my own just for this 1 stepper and all i have are these PN2907 transistors. How can i make this work if at all thanks for any info :)

Stepper: EM-257


Transistors: PN2907


also i would like to run it off 9 volts and it uses 7 but ik how to do that.


To be practical, you can't do it all with only PNP transistors.
You'll need some NPN transistors, too.

When all else fails, check your wiring!


The transistor you quote cannot handle the current at all.  It's saturation voltage is above 1.6V at 700mA, so it
will just melt (max power 0.6W).  Also the DC gain at high current on that transistor is way too low (falling below
30 at above 500mA).

Find transistors able to carry 2 or 3A, and you have a chance of getting devices that still have usable gain
and saturation at 0.7A.  For instance STX724 (NPN) and STX790A (PNP) would be suitable.  Modern superbeta
transistors can take 2 or more amps in a small package due to superbly low saturation voltages.  Older
transistor designs cannot.

How many wires is your motor?  Driving unipolar will be a bit simpler and just need NPN transistors.  You
can also use darlingtons (but they will probably need heatsinking).   Flyback diodes are needed for each
winding too.

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