justDIY
Active Member
I recently got inspired to mess around with some steppers I salvaged from old printers. I tossed together a real quick driver based on a uln2803, and toasted it trying to drive the 1a stepper. It ran the ~300ma stepper ok, but got kinda hot. Using one '595, I have control for two unipolar motors.
So, I looked around a bit, and decided to build version two using discrete switches instead of an array. A lot of designs I dug up used darlingtons instead of mosfets. Is there some advantage to using a bjt verses a fet in this application? It would seem to me the very low voltage drop in a fet would be an advantage, and given improvements in "logic level" fets, having a low gate voltage seems ok for at least a few amps.
anyway, here's the 1000 words:
**broken link removed**
fets:
Fairchild HUF76407, logic level, to-251aa package
flyback diode:
12a surge schottky diode
control:
3-wire serial interface, expandable
logic supply:
5v regulated and filtered
motor supply:
1a current limited, up to 12v
So, I looked around a bit, and decided to build version two using discrete switches instead of an array. A lot of designs I dug up used darlingtons instead of mosfets. Is there some advantage to using a bjt verses a fet in this application? It would seem to me the very low voltage drop in a fet would be an advantage, and given improvements in "logic level" fets, having a low gate voltage seems ok for at least a few amps.
anyway, here's the 1000 words:
**broken link removed**
fets:
Fairchild HUF76407, logic level, to-251aa package
flyback diode:
12a surge schottky diode
control:
3-wire serial interface, expandable
logic supply:
5v regulated and filtered
motor supply:
1a current limited, up to 12v