I'm using a Microchip TC646 temperature-regulated, PWM speed controller circuit to regulate the speed of a 48vdc fan.
The recommended circuit in the datasheet has fixed upper and lower speed limits using fixed resistors (p. 16):
http://ww1.microchip.com/downloads/en/DeviceDoc/21446D.pdfIf I want to change this circuit so that the limits can be adjusted via pots, which resistors should be replaced with pots? Is this as straightforward as using trimmers in place of R1 & R3?
Also, Microchip makes another series of chips, the TC642/647. What's the difference from the 646? (The complete family is 642, 646, 647, 648, 649.) The datasheets read as duplicates except for the Behavioral Algorithm.
Thanks,
iX