Temperature is controlled by regulating the fan speed of the fan. In user mode, the user has control over the speed of the fan via 2 trimpots (right side of Fig. 1) that directly adjusts the fan supply voltage from ~7-12V. In autonomous mode, Fan 1 is controlled by voltage regulation with a 4-bit R-2R DAC that is optoisolated from the fan motors. An enable pin switches the fan on/off with a TIP31A NPN transistor.
May 5th, 2008