A phase-control power controller that converts a line voltage to an RMS load voltage includes an analog load voltage sensor that includes a light emitter that provides an optical output related to an RMS load voltage, and a phase-control circuit that has a comparison circuit that varies a resistance in the phase-control circuit responsive to the optical output. The comparison circuit includes an optically coupled transistor that senses the optical output from the light emitter, a load sensitive resistor that emits an amount of thermal energy corresponding to an amount of optical energy sensed by the optically coupled transistor, and two thermally dependent resistors connected in series, where one of the two resistors has a resistance that corresponds to the amount of thermal energy emitted by the load sensitive resistor and that varies the resistance in the phase-controlled dimming circuit.