Hi. I want to drive a bipolar stepper motor marked 1.4V 3.8A. I have built a PIC16F628 based circuit to drive two H-bridges made up of 2N3904/06 transistors. Clearly they will not supply enough power. The PCB is already made, so I won't be changing the transistors on it.
What are my options for boosting the 5V low current output of the H-bridges? (There are 1K resistors to the bases of all the transistors. If I lower them, how low can I go before I start to cause problems with the PIC?) I'm thinking of rummaging around for four relays, and using one diode per coil to choose which coil gets energized, based on the current direction. I'm worried about speed (1.8 degrees per step!), and burning out the relay contacts, but I'd rather get results at all.
Would I be able to use the same diode trick with power transistors? If so, which ones would you recommend? Note: So far I spent only $1, which was for the super glossy paper I used for the toner transfer for etching the PCB. Everything else came from my junkbox, so I'm loathe to spend any (significant) coin. It's a matter of pride, you understand. :)
Assuming I zipped the right files, you can download the Eagle project from
Thanks for any advice.
- Owen -
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