PWM op amp transistor (1)

PWM controlled by R7 sensor (light, temperature, etc) or potenciometer. The op-amps generate a square wave, then a triangle shape to compare with the voltage divider with sensor, drives a small PNP transistor. A NTC can be on R7, R6 and R12 adjusted accordingly for specific temperature control, PNP can drive a small 80/120mm 12V Fan.