dc42:
- The flyback diode is on the wrong place in that schematic, it doesn't protect the transistor when the motor switches off. For that, you need a flyback diode connected in parallel with the motor.
Agreed. Thanks for catching this, maybe a bit too early on Sunday for me. Updated schematic attached.
- IMO darlingtons should almost never be used, because they have high saturation voltage. If the motor draws a substantial current, this results in a lot of power being dissipated in the darlington, so it will get hot and need a heatsink.
Not sure I agree it would be a factor in this particular case but generally, I do agree.
A power mosfet is a much better solution in such a case.
I agree. The MOSFET would be my first choice as a switch like this. We were talking about transistors though.
If the current is not so high (say 500mA or less), then a single transistor will do the job more efficiently and with less heat generation than a darlington, especially if the transistor is a high gain low saturation type such as the ZTX851.
Yes, very true. The ZTX851 looks like a pretty good choice.
For what it's worth, the updated schematic now shows the ZTX851.
