Boost converter with a pulse frequency modulation mode for operating above an audible frequency

Patent metadata

Field	Value
Publication number	US-9345083-B2
Application number	US-201414503037-A
Country	US
Kind code	B2
Filing date	Sep 30, 2014
Priority date	Oct 30, 2013
Publication date	May 17, 2016
Grant date	May 17, 2016

Abstract

The embodiments discussed herein relate to systems, methods, and apparatus for executing a pulse frequency modulation (PFM) mode of a boost converter in order to ensure that a switching frequency of the boost converter is a above an audible frequency threshold. In this way, a user operating a display device that is controlled by the boost converter will not be disturbed by audible noises generated at the display device. The PFM mode enforces an audible frequency threshold by using control circuitry designed to increase or decrease the frequency of a pulse signal depending on how the frequency of the pulse signal changes over time. The control circuitry can apply an additional load to the boost converter in order to increase the frequency of the pulse signal when the frequency is approaching the audible frequency threshold.

First claim

What is claimed is:

1. A control circuit for a display device, the control circuit comprising:
a boost circuit configured to output a switching signal to a subsystem of the display device based on a minimum frequency threshold; and
a timing circuit configured to detect pulses in the switching signal, wherein, when the timing circuit does not detect a pulse in the switching signal before a cycle period of the timing circuit expires, the cycle period restarts and timing circuit causes the boost circuit to output a supplemental pulse to ensure that a frequency of the switching signal stays above the minimum frequency threshold.

2. The control circuit of claim 1 , wherein the timing circuit is configured to restart the cycle period when the timing circuit detects the pulse before the cycle period expires.

3. The control circuit of claim 2 , wherein the cycle period corresponds to a frequency that is at least 20 kilohertz.

4. The control circuit of claim 1 , wherein the timing circuit is configured to turn on a current sink of the boost circuit when the frequency of the switching signal is approaching or below the minimum frequency threshold.

5. The control circuit of claim 4 , wherein the timing circuit is configured to turn off the current sink of the boost circuit when the timing circuit detects the pulse in the switching signal before the cycle period expires.

6. The control circuit of claim 1 , further comprising:
a voltage detector electrically coupled to a capacitor of the subsystem, wherein the voltage detector is configured to detect a capacitor voltage and enable a current sink in order to discharge the capacitor when the capacitor voltage reaches or exceeds a capacitor voltage threshold.

7. The control circuit of claim 6 , wherein the voltage detector is further configured to discharge the capacitor to a nominal charge level for supplementing a charge signal provided to a series of light emitting diodes (LEDs) of the display device.

8. A machine-readable non-transitory storage medium storing instructions that, when executed by a processor included in a computing device, cause the computing device to carry out steps that include:
generating a switching signal for a subsystem of a display device based on a minimum frequency threshold; and
generating a supplemental pulse when a pulse is not detected in the switching signal during a cycle period, wherein the cycle period is reset when the pulse is generated and the cycle period corresponds to a frequency that is equal to or greater than the minimum frequency threshold.

9. The machine-readable non-transitory storage medium of claim 8 , wherein the steps further include:
restarting the cycle period upon detecting the pulse before the cycle period expires.

10. The machine-readable non-transitory storage medium of claim 9 , wherein the minimum frequency threshold corresponds to a frequency that is at least 20 kilohertz.

11. The machine-readable non-transitory storage medium of claim 8 , wherein the steps further include:
turning on a current sink when a frequency of the switching signal is approaching or below the minimum frequency threshold.

12. The machine-readable non-transitory storage medium of claim 8 , wherein the steps further include:
turning off a current sink when the pulse is detected in the switching signal before the cycle period expires.

13. The machine-readable non-transitory storage medium of claim 8 , wherein the steps further include:
detecting a capacitor voltage and enabling a current sink in order to discharge a capacitor when the capacitor voltage reaches or exceeds a capacitor voltage threshold.

14. The machine-readable non-transitory storage medium of claim 13 , wherein the steps further include:
enabling the current sink in order to discharge the capacitor to a nominal voltage level for supplementing a charge signal provided to a series of light emitting diodes (LEDs) of the display device.

15. A computing device, comprising:
a processor; and
a display device, comprising:
a boost circuit configured to output a switching signal to a subsystem of the display device based on a minimum frequency threshold; and
a timing circuit configured to detect pulses in the switching signal during a cycle period, wherein, when the timing circuit does not detect a pulse in the switching signal before the cycle period expires, the cycle period restarts and the timing circuit causes the boost circuit to output a supplemental pulse into with the switching signal.

16. The computing device of claim 15 , wherein the timing circuit is configured to restart the cycle period when the timing circuit detects the pulse before the cycle period expires.

17. The computing device of claim 16 , wherein the cycle period corresponds to a frequency that is at least 20 kilohertz.

18. The computing device of claim 15 , wherein the timing circuit is configured to turn on a current sink of the boost circuit when the timing circuit does not detect the pulse in the switching signal before the cycle period expires.

19. The computing device of claim 15 , wherein the timing circuit is configured to turn off a current sink of the boost circuit when the timing circuit detects the pulse in the switching signal before the cycle period expires.

20. The computing device of claim 15 , further comprising:
a voltage detector electrically coupled to a capacitor of the subsystem, wherein the voltage detector is configured to detect a capacitor voltage and enable a current sink in order to discharge the capacitor when the capacitor voltage reaches or exceeds a capacitor voltage threshold.

Assignees

• Apple Inc

Inventors

• Hussain Asif
• Mohtashemi Behzad
• Navabi-Shirazi Mohammad J
• Chen Jingdong
• Pandya Manisha P

Classifications

• G09G3/342 Primary

  using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines · CPC title

• G09G2320/064

  by time modulation of the brightness of the illumination source · CPC title

• G09G3/3406

  Control of illumination source (illumination devices structurally associated with liquid crystal cells G02F1/1336) · CPC title

• G09G2310/08

  Details of timing specific for flat panels, other than clock recovery · CPC title

• G09G2320/0233

  Improving the luminance or brightness uniformity across the screen · CPC title