Quiet fan speed control

Details Quiet fan speed control Quiet fan speed control

2005-08-02

2005-08-02

Sircus, Brian (Department: 2836)

Electrical transmission or interconnection systems

Switching systems

Condition responsive

Reexamination Certificate

active

06924568

ABSTRACT:
A novel a circuit for driving a fan includes an output terminal for supplying the fan with drive power, a pulse width modulation driver, and a limiter. A first power terminal of the fan is held at a first voltage (e.g., 0V), and a second power terminal of the fan is coupled to the output terminal of the driver circuit. The PWM driver provides a series of fan drive pulses on the output terminal, and the limiter prevents the voltage on the output terminal from falling below a predetermined voltage. The predetermined voltage is greater than the first voltage at which the fan's first power terminal is held, and is sufficient to keep the fan in motion even when the duty cycle of the PWM signal is 0%. In a particular embodiment the limiter includes a voltage clamp. In a more particular embodiment, the voltage clamp is a diode. In another particular embodiment, the limiter includes a switch for combining a PWM signal with a DC voltage at an output.

REFERENCES:
patent: 5929581 (1999-07-01), Van Brocklin et al.
patent: 5990582 (1999-11-01), Henderson et al.
patent: 6182902 (2001-02-01), Shih
patent: 6239991 (2001-05-01), Ajro et al.
patent: 6590356 (2003-07-01), Smith et al.
patent: 6617709 (2003-09-01), Yu

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