Parabolic control of the duty cycle of a pulse width modulated signal

• US 20040232869A1
• Filed: 05/19/2003
• Published: 11/25/2004
• Est. Priority Date: 05/19/2003
• Status: Active Grant

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Standard Microsystems Corporation (Microchip Technology Incorporated)
• Inventors: Marando, Eileen M., Schoepflin, Robert W.
• Granted Patent: US 6,933,697 B2
• Time in Patent Office: Days
• US Class Current: 318/599
• CPC Class Codes: G05B 11/28 using pulse-height modulation; using pulse-width modulation

Abstract

A system may include control logic and a PWM generator configured to generate a PWM (Pulse Width Modulated) signal. The PWM generator is configured to generate the duty cycle of the PWM signal dependent on a duty cycle value generated by the control logic. The control logic stores an inverse focal point value and is configured to generate the duty cycle value by processing the inverse focal point value and a temperature value indicating a current temperature according to the equation of a parabola.

Claims

1. A system, comprising:

a PWM generator configured to generate a PWM (Pulse Width Modulated) signal having a duty cycle, wherein the PWM generator is configured to generate the duty cycle of the PWM signal dependent on a duty cycle value; and

control logic coupled to the PWM generator and configured to store an inverse focal point value, wherein the control logic is configured to generate the duty cycle value by processing the inverse focal point value and a temperature value indicating a current temperature according to an equation of a parabola.

2. The system of claim 1, wherein the control logic is configured to store a minimum temperature value, wherein the control logic is configured to generate the duty cycle value dependent on the minimum temperature value.

3. The system of claim 2, wherein the control logic is configured to update the minimum temperature value and the inverse focal point value.

4. The system of claim 1, wherein the control logic is configured to generate the duty cycle value by processing the temperature value according to an equation of a parabola at a coordinate origin and shifting a result of the equation into a range of operable duty cycle values.

5. The system of claim 1, wherein the control logic is configured to generate the duty cycle value by:

generating an uncompensated duty cycle value proportional to a square of a temperature delta value multiplied by the inverse focal point value, wherein the temperature delta value equals the temperature value minus a minimum temperature value; and

generating the duty cycle value by adding a minimum duty cycle value to the uncompensated duty cycle value.

6. The system of claim 1, wherein the control logic is configured to selectively vary the duty cycle of the PWM signal less at higher temperature values if the temperature is stabilizing than if the temperature is increasing.

7. A method, comprising:

powering a fan according to a PWM (pulse width modulated) signal;

storing an inverse focal point value;

processing the inverse focal point value and a temperature value representing a current temperature according to an equation of a parabola to generate a duty cycle value; and

generating a duty cycle of the PWM signal dependent on the duty cycle value.

8. The method of claim 7, further comprising storing a minimum temperature value, wherein said generating a duty cycle value comprises generating the duty cycle value dependent on the values of the minimum temperature value.

9. The method of claim 8, further comprising updating at least one of:

the minimum temperature value and the inverse focal point value.

10. The method of claim 7, wherein said generating a duty cycle value comprises:

processing the temperature value according to an equation of a parabola at a coordinate origin;

generating the duty cycle value by shifting a result of said processing into a range of operable duty cycle values.

11. The method of claim 7, wherein said generating a duty cycle value comprises:

generating an uncompensated duty cycle value proportional to a square of a temperature delta value multiplied by the inverse focal point value, wherein the temperature delta value equals the temperature value minus a minimum temperature value; and

generating the duty cycle value by adding a minimum duty cycle value to the uncompensated duty cycle value.

12. The method of claim 7, further comprising selectively varying the duty cycle of the PWM signal less at higher values of the temperature if the temperature is stabilizing than if the temperature is increasing.

13. A system, comprising:

means for powering a fan according to a PWM (pulse width modulated) signal having a duty cycle dependent on a duty cycle value;

means for generating the duty cycle value, wherein the means for generating store an inverse focal point value and process the inverse focal point value and a temperature value representing a current temperature according to an equation of a parabola to generate the duty cycle value.