Preamplifier fly height control (FHC) driver and sensing circuit

Managing temperature of a read/write head in a disk drive system in which there is a power variance due to different operation modes. A circuit device determines and delivers additional power needed for compensating for the temperature variance due to different operational power requirements. The power is delivered to a resistive heater (Rheat) associated with the head. The compensating power is based on the delivery voltage, delivery current, and resistance of the resistive heater (Rheat). The delivery current is varied to account for changes in the resistance of the resistive heater (Rheat) since it can vary with temperature. By sensing the current with a sensor, the resistance is determined via the sensed current and the delivery voltage. The current is adjusted for maintaining the compensating power.