Variable Power Regulator Mystery DAMMITDAMMITDAMMIT!!!!
May 16, 2013
I suppose I shouldn't be complaining. After all, the circuit works:
...and more or less this (the cap straddles the gutter on my board but Fritzing is limited...)
There's no connection to pin 3, which is "output" supposedly. Yet it works as a voltage controller-from 18v to 3v-12v (range.)
I based this off of the old Mims circuit on p.76 of the Engineer's Notebook II but made a few adjustments, obviously. First, I barely got 1v of variation (4v-5v) with the 50kΩ pot. When I took out the 1.2kΩ resistor going from the wiper to the output rail, I started to get a little more. With a 100KΩ pot plus a 10kΩ resistor in serial making up "R1," I get a useful range.
My gut tells me it shouldn't work, but my multimeter tells me it does. Is it just some kind of bass-ackward voltage division at this point? The output isn't coming from between a pair of resistors. Is this chip designed to work this way? I feel like this: