Patent ID: 8188731

Claim:
A controller comprising: a control circuit comprising a closed loop circuit, the closed loop circuit comprising: an input; an output; a forward path coupled to the input and to the output; a feedback path coupled to the input and to the output; and a sensor having a sensitivity, the sensor being in the forward path or in the feedback path, the sensor for generating a sensor signal; an error signal generator that is external to the closed loop circuit, the error signal generator to generate an error signal and to provide the error signal to the closed loop circuit such that the error signal is incorporated into a useful signal of the closed loop circuit, wherein the error signal has a preselected magnitude, the closed loop circuit being configured to generate an output signal at the output, the output signal being based on the sensor signal and the error signal, the output signal being sent along the feedback path to the input; and a detector configured to detect a change in the sensitivity of the sensor, the detector being coupled to the forward path, the detector to generate a control signal; wherein the forward path comprises a control device, which is coupled to the output, to limit an output signal at the output to a predetermined value, the detector to control the control device using the control signal.