Circuit and method for controlling pulse width modulation of a current suply for a load

Patent metadata

Field	Value
Publication number	US-2017071041-A1
Application number	US-201515118984-A
Country	US
Kind code	A1
Filing date	Jan 30, 2015
Priority date	Feb 14, 2014
Publication date	Mar 9, 2017
Grant date	—

Abstract

A circuit comprising a controller ( 2 ) for controlling a pulse width modulated input signal, and a driver ( 4 ) configured to supply current to a load ( 6 ) based on the input signal, wherein over the on time of each pulse width modulation period the driver ( 4 ) supplies current to the load ( 6 ) with a second frequency that is greater than the first frequency. The controller ( 2 ) is configured to control the duty cycle to set the output of the load ( 6 ) to a desired output level, and to dither the duty cycle about a point corresponding to the desired output level.

First claim

1 . A circuit comprising:
A driver; and a controller for controlling a pulse width modulated input signal applied to the driver, the input signal having a period comprising an on time and on off time with said period repeating at a first frequency, and the controller being configured to control a duty cycle of the input signal being a proportion of the on time relative to the period or off time; wherein the driver is configured to supply current to a load based on the input signal, wherein over the off time of each period the driver withholds supply of current from a power supply to the load, and over the on time of each period the driver supplies current from the power supply to the load but with a second frequency that is greater than the first frequency, the load thus generating an output at a level dependent on the duty cycle; wherein the controller is configured to control the duty cycle to set the output of the load to a desired output level, and to dither the duty cycle about a point corresponding to the desired output level; and wherein the circuit further comprises a feedback channel from the driver to the controller for measuring the second frequency, wherein the controller is configured to adapt the dithering of the duty cycle in dependence on the second frequency as measured via said feedback channel.

2 . (canceled)

3 . The circuit of claim 1 , wherein the controller is configured to control the duty cycle to switch the output of the load to a plurality of different output levels, and said dithering comprises dithering the duty cycle about each of a plurality of points corresponding to said different output levels respectively.

4 . The circuit of claim 1 , wherein the load comprises a light source and the output comprises light emitted by the light source.

5 . The circuit of claim 4 , wherein the controller is configured to control the duty cycle to switch the light emitted by the load to a plurality of different light output levels.

6 . The circuit of claim 5 , wherein the controller is configured to code a data signal into said light by using the different output levels to signal symbols of the data signal.

7 . The circuit of claim 5 , wherein the controller is configured to perform said dithering by dithering the duty cycle about each of a plurality of points corresponding to the different light output levels respectively.

8 . The circuit of claim 1 , wherein:
the output of the load varies according to a relationship between the duty cycle and the level of the output; and the first and second frequencies in combination result in a pattern in the relationship between the duty cycle and the level of the output that repeats in regular intervals of the duty cycle.

9 . The circuit of claim 8 , wherein the load comprises a light source and the output comprises light emitted by the light source, said relationship being between the duty cycle and the level of said light.

10 . The circuit of claim 1 , wherein the duty cycle is dithered in a plurality n of discrete steps about said point or about each of said points.

11 . The circuit of claim 10 wherein the duty cycle is dithered about said point or each of said points in n steps of P/n where P is a period of said regular intervals of the duty cycle.

12 . The circuit of claim 10 , wherein the dithering is random with each of the n steps having a 1/n probability of being selected per period.

13 . The circuit of claim 1 , wherein the driver is a buck converter.

14 . The circuit of claim 2 , wherein the feedback channel comprises a voltage divider or a differential circuit.

15 . A computer program product comprising code embodied on a computer-readable storage medium and adapted so as when executed on one or more processors to perform operations of:
causing a pulse width modulated input signal to be provided to a driver which supplies current to a load based on the input signal, wherein the input signal has a period comprising an on time and on off time with said period repeating at a first frequency, and wherein over the off time of each period the driver withholds supply of current from a power supply to a load, and over the on time of each period the driver supplies current from the power supply to the load with a second frequency that is greater than the first frequency; controlling a duty cycle of the input signal being a proportion of the on time relative to said period or off time, in order to set the output of the load to a desired output level; and dithering the duty cycle about a point corresponding to the desired output level.

Assignees

• Philips Lighting Holding Bv

Inventors

• Baggen Constant Paul Marie Jozef
• Nijssen Stephanus Joseph Johannes

Classifications

• H03K7/08 Primary

  Duration or width modulation {; Duty cycle modulation} · CPC title

• H05B45/00 Primary

  Circuit arrangements for operating light-emitting diodes [LED] · CPC title

• H05B45/10

  Controlling the intensity of the light · CPC title

• H05B33/0845 Primary

  Electricity · mapped topic

• H05B33/0815

  Electricity · mapped topic