Method and apparatus for determining a target light intensity from a phase-control signal

• US 10,070,507 B2
• Filed: 10/13/2017
• Issued: 09/04/2018
• Est. Priority Date: 05/10/2011
• Status: Active Grant

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Lutron Electronics Company Incorporated (Lutron Electronics)
• Inventors: Hausman, Jr., Donald F.
• Primary Examiner(s): Laxton, Gary L
• Application Number:
  US15/783,604
• Publication Number:
  US 20180042093A1
• Time in Patent Office: 326 Days
• CPC Class Codes: H02M 1/08 Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
• CPC Class Codes: H05B 41/2828 using control circuits for the switching elements H05B41/2827 takes precedence
• CPC Class Codes: H05B 41/295 with semiconductor devices and specially adapted for lamps with preheating electrodes, e.g. for fluorescent lamps
• CPC Class Codes: H05B 41/3924 by phase control, e.g. using a triac H05B41/3922 takes precedence
• CPC Class Codes: H05B 41/3925 by frequency variation H05B41/3922 takes precedence
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/39 Circuits containing inverter bridges
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A dimmable ballast circuit for a compact fluorescent lamp controls the intensity of a lamp tube in response to a phase-control voltage received from a dimmer switch. The ballast circuit comprises a phase-control-to-DC converter circuit that receives the phase-control voltage, which is characterized by a duty cycle defining a target intensity of the lamp tube, and generates a DC voltage representative of the duty cycle of the phase-control voltage. Changes in the duty cycle of the phase-control voltage that are below a threshold amount are filtered out by the converter circuit, while intentional changes in the duty cycle of the phase-control voltage are reflected in changes in the target intensity level and thereby the intensity level of the lamp tube.

Claims

1. An apparatus for controlling an intensity level of a lighting load, the apparatus configured to receive a phase-control voltage characterized by a duty cycle, the apparatus comprising:

a load regulation circuit configured to receive a drive control signal and to control the intensity level of the lighting load in response to the drive control signal; and

a control circuit configured to receive a signal representative of the intensity level of the lighting load, and to generate the drive control signal to cause the load regulation circuit to adjust the intensity level of the lighting load towards a target level;

wherein the control circuit is configured to determine the target level for the lighting load in response to the duty cycle of the phase-control voltage, the control circuit configured to adjust the target level for the lighting load using a first time constant in response to changes in the duty cycle of the phase-control voltage that are less than a threshold amount, and to adjust the target level for the lighting load using a second time constant in response to changes in the duty cycle of the phase-control voltage that are greater than the threshold amount, where the second time constant is less than the first time constant.

2. The apparatus of claim 1, wherein the control circuit comprises a processing device configured to use a digital low-pass filter to determine the target level for the lighting load in response to the phase-control voltage.

3. The apparatus of claim 2, wherein the processing device is configured to receive a scaled version of the phase-control voltage, and measure a duty cycle of the scaled version of the phase-control voltage, the processing device further configured to determine a requested level in response to the duty cycle of the scaled version of the phase-control voltage, and process the requested level using the digital low-pass filter to determine the target level.

4. The apparatus of claim 3, wherein the processing device is configured to determine a change in the duty cycle of the scaled version of the phase-control voltage by calculating a difference between the requested level and the target level.

5. The apparatus of claim 4, wherein the processing device is configured to adjust a pole of the digital low-pass filter to set a passband frequency of the digital low-pass filter to a first frequency when the change in the duty cycle of the scaled version of the phase-control voltage is less than a change threshold.

6. The apparatus of claim 5, wherein the processing device is configured to adjust a pole of the digital low-pass filter to set a passband frequency of the digital low-pass filter to a second frequency when the change in the duty cycle of the scaled version of the phase-control voltage is greater than the change threshold.

7. The apparatus of claim 6, wherein the change threshold is dependent upon the target level for the lighting load.

8. The apparatus of claim 2, wherein the processing device is configured to sample the signal representative of the intensity level of the lighting load and determine an actual level of the lighting load from the sampled signal representative of the intensity level of the lighting load, the processing device configured to calculate an error between the actual level and the target level.

9. The apparatus of claim 8, wherein the processing device is configured to control the drive control signal in response to the error to adjust the intensity level of the lighting load towards the target level.

10. The apparatus of claim 2, wherein the processing device comprises a microprocessor.

11. The apparatus of claim 1, wherein the control circuit is configured to convert the phase-control voltage into a target signal that is representative of the target level of the lighting load, the control circuit configured to produce the drive control signal by comparing a magnitude of the target signal and a magnitude of the signal representative of the intensity level of the lighting load.

12. The apparatus of claim 11, wherein the control circuit comprises a first filter circuit configured to generate a filtered voltage in response to the phase-control voltage, the control circuit configured to adjust the magnitude of the target signal in response to changes in the duty cycle of the phase-control voltage that cause a magnitude of the filtered voltage to change by an amount in excess of a threshold voltage.

13. The apparatus of claim 12, wherein the control circuit comprises a second filter circuit configured to filter the filtered voltage to generate the target signal, the second filter circuit configured to have the first time constant when the filtered voltage increases or decreases by an amount less than the threshold voltage, and have the second time constant when the filtered voltage increases or decreases by an amount greater than the threshold voltage.

14. The apparatus of claim 1, wherein the lighting load comprises a LED light source and the load regulation circuit comprises an LED driver circuit.

15. A method of controlling an intensity level of a lighting load, the method comprising:

receiving a phase-control voltage, the phase-control voltage characterized by a duty cycle;

determine a target level for the lighting load in response to the duty cycle of the phase-control voltage;

receiving a signal representative of the intensity level of the lighting load;

generating a drive signal to adjust the intensity level of the lighting load towards the target level;

adjusting the target level of the lighting load using a first time constant in response to changes in the duty cycle of the phase-control voltage that are less than a threshold amount; and

adjusting the target level of the lighting load using a second time constant in response to changes in the duty cycle of the phase-control voltage that are greater than the threshold amount;

wherein the second time constant is less than the first time constant.

16. The method of claim 15, further comprising:

receiving a scaled version of the phase-control voltage;

measuring a duty cycle of the scaled version of the phase-control voltage;

determining a requested level in response to the duty cycle of the scaled version of the phase-control voltage; and

processing the requested level using a digital low-pass filter to determine the target level.

17. The method of claim 16, further comprising:

determine a change in the duty cycle of the scaled version of the phase-control voltage by calculating a difference between the requested level and the target level;

comparing the change in the duty cycle of the scaled version of the phase-control voltage to a change threshold; and

adjusting a pole of the digital low-pass filter to set a passband frequency of the digital low-pass filter in response to the comparison between the change in the duty cycle and the change threshold;

wherein the passband frequency of the digital low-pass filter is set to a first frequency when the change in the duty cycle of the scaled version of the phase-control voltage is less than the change threshold, and to a second frequency when the change in the duty cycle of the scaled version of the phase-control voltage is greater than the change threshold.

18. The method of claim 17, further comprising:

determining the change threshold based upon the target level for the lighting load.

19. The method of claim 15, further comprising:

sampling the signal representative of the intensity level of the lighting load;

determining an actual level of the lighting load from the sampled signal representative of the intensity level of the lighting load;

calculating an error between the actual level and the target level; and

controlling the drive control signal in response to the error to adjust the intensity level of the lighting load towards the target level.

20. The method of claim 15, further comprising:

filtering out changes in the duty cycle of the phase-control voltage that are below the threshold amount.