Proportional integral fan controller for electronic device

An electronic device, comprising:

• a case having a local environment temperature within the case,
• a reference temperature, and a steady state local environment temperature condition when the local environment temperature equals the reference temperature;
• a fan having a speed and a rate of change of fan speed;
• a temperature sensor for detecting the local environment temperature inside the case, the temperature sensor exhibiting a lag time for indicating actual local environment temperature, the lag time of the temperature sensor creates a system response pole within the control circuitry;
• and
• control circuitry connected to the temperature sensor and the fan, the control circuitry implementing closed loop control over the fan to vary the speed of the fan in a manner which cancels out the lag time of the temperature sensor during the steady state local environment temperature condition of the electronic device, wherein during the steady state local environment temperature condition of the electronic device the rate of change of the speed of the fan varies in proportion to variation in detected local environment temperature, wherein the control circuitry comprises a bridge circuit and an integrator circuit, the bridge circuit including the temperature sensor, the bridge circuit generating a first signal and a second signal, the first signal varying with changes in the resistance of the temperature sensor, the second signal equal to the first signal when the temperature sensor detects a temperature equal to the reference temperature, and wherein the integrator circuit is responsive to the first signal and the second signal to generate an output signal which is driven active while the detected temperature exceeds the reference temperature and which the output signal is driven into an off state while the detected temperature does not exceed the reference temperature, the integrator circuit including a compensation network which cancels out the system response pole during the steady state local environment temperature condition of the electronic device;
• and
• wherein the compensation network is a RC network occurring along the feedback path of the integrator circuit, the feedback path routing the output signal via the compensation network to an input of the integrator circuit which receives the second signal.

A method for controlling fan speed in proportion to heat generated within an electronic device case internal environment, comprising the steps of:

• generating a first signal which varies as a function of temperature detected at a temperature sensor, wherein the temperature sensor exhibits a response lag before indicating actual detected temperature equal to local environment temperature around the temperature sensor, the temperature sensor being within the electronic device case;
• generating a reference signal corresponding to a reference temperature;
• integrating a difference between the first signal and the reference signal to derive an output signal having a rate of change, the output signal driven active while the first signal exceeds the reference signal;
• during the step of integrating, canceling a control loop pole corresponding to the response lag of the temperature sensor;
• buffering the output signal at a buffer to derive a control signal having a rate of change which drives a motor of a cooling fan having a first speed and a rate of change of fan speed within the electronic device case;
• cooling the electronic device case internal environment with the cooling fan at the first speed to reduce the temperature detected by the temperature sensor;
• reducing the output signal and control signal as the detected temperature approaches the reference temperature, wherein fan speed decreases below the first speed as the control signal is reduced;
• and
• varying the rate of change of the output signal and the rate of change of the control signal proportionally with increases and decreases in detected temperature while the detected temperature exceeds the reference temperature, and correspondingly varying the rate of change of the speed of the fan so as to bias the detected temperature toward a steady state temperature condition in the electronic device internal environment where the detected temperature equals the reference temperature.