Coincidental to the thread which has been running on mini-drills, I’ve been looking at alternative circuits to the usual pulse-width speed controllers. The problem with those is that they are unable to compensate for loading of the drill. I found a number of circuits where the current drawn by the drill is sensed so as to provide a signal which is fed to a voltage regulator, so that when loading and increased current occurs, the regulator will supply increase the voltage, attempting to maintain the speed.
The circuit which is attached originates from this website
http://quan-diy.com/projects/drillco...lspeedcont.htm, but I have re-drafted it to clarify what is going on. Unfortunately, my first attempt to construct this is not (yet) working; the drill just runs at full speed; maybe a problem on the PCB.
If there’s a problem with the circuit, it isn’t apparent to me and I’d appreciate any thoughts about its viability.
Thanks
B