Been a long time since I've looked over this sort of thing, so take this with a grain of salt.
First off, you're using PNP transistors, which IIRC are generally a bit less efficient than NPN and require more current in cutoff. Consider switching to NPN.
It looks generally workable to me, although I wonder a bit about having two large, different inductances (the motor and the relay) there. It seems like a recipe for sparking at the switch and possible a bit of weird motor jerking. You might consider a largeish capacitor somewhere in the general vicinity of M1/Q2/U1. Shorting M1 with a capacitor will reduce sparking, while shorting Q2 with a capacitor might also reduce the chance that motor load jitter burns out Q2. Or just get a really huge Q2.
Oh, and a fuse. Always a fuse for anything driving a motor.
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Date: 2006-12-14 12:46 pm (UTC)First off, you're using PNP transistors, which IIRC are generally a bit less efficient than NPN and require more current in cutoff. Consider switching to NPN.
It looks generally workable to me, although I wonder a bit about having two large, different inductances (the motor and the relay) there. It seems like a recipe for sparking at the switch and possible a bit of weird motor jerking. You might consider a largeish capacitor somewhere in the general vicinity of M1/Q2/U1. Shorting M1 with a capacitor will reduce sparking, while shorting Q2 with a capacitor might also reduce the chance that motor load jitter burns out Q2. Or just get a really huge Q2.
Oh, and a fuse. Always a fuse for anything driving a motor.