Thanks dknguyen, that's very helpful.
The application I have in mind is to drive a 3v motor with 12v, at very low power, well within the motor's capability. But I'm trying to figure out the principles, so to take your extreme example of a 10v motor and 1000v supply, no that does not sound reasonable, but I want to understand all the factors that should be taken into account when making such a decision.
So I'll start a list:
- PWM duty cycle must be low enough to avoid overheating motor
- Voltage applied to motor must not be enough to break down winding insulation
Are there any more factors? Particularly regarding noise and efficiency?
Also, on the subject of adding a buck converter, I'm trying to keep the part count of my circuit as low as possible, so I want to look at ways to exploit the inductance of the motor to smooth current flow. But I want bi-directional control, so I need an H-bridge, which complicates things a little. I might have an idea about that though, which I'll post later if I have time. For now I want to complete my list!