ADAPTIVE DIMMER DETECTION AND CONTROL FOR LED LAMP

• US 20110012530A1
• Filed: 07/14/2009
• Published: 01/20/2011
• Est. Priority Date: 07/14/2009
• Status: Active Grant

• Current Assignee: Dialog Semiconductor Incorporated (Renesas Electronics Corporation)
• Original Assignee: iWatt, Inc. (Renesas Electronics Corporation)
• Inventors: Chen, Baorong, Myers, Richard M., Zheng, Junjie, Chen, Gordon, Kesterson, John W.
• Granted Patent: US 8,222,832 B2
• Time in Patent Office: Days
• US Class Current: 315/294
• CPC Class Codes: H02M 1/007 Plural converter units in cascade push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826
• CPC Class Codes: H02M 1/4225 using a non-isolated boost converter
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/385 using flyback topology
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

An LED lamp is provided in which the output light intensity of the LEDs in the LED lamp is adjusted based on the input voltage to the LED lamp. A dimmer control unit detects a type of dimmer switch during a configuration process. Using the detected dimmer type, the dimmer control unit generates control signals appropriate for the detected dimmer type to provide regulated current to the LEDs and to achieve the desired dimming effect. The LED lamp can be a direct replacement of conventional incandescent lamps in typical wiring configurations found in residential and commercial building lighting applications that use conventional dimmer switches.

Claims

1. A light-emitting diode (LED) lamp, comprising:

one or more LEDs;

a dimmer control unit configured to determine a type of dimmer switch providing an input voltage, determine a detected dimming amount of the input voltage for the detected type of dimmer switch, and generate one or more control signals to control regulated current through the LEDs such that an output light intensity of the LEDs is proportional to the detected dimming amount; and

a power converter configured to receive the control signals and provide regulated current to the one or more LEDs, the power converter configured to adjust the regulated current to the one or more LEDs as indicated by the control signals to achieve the output light intensity proportional to the detected dimming amount.

2. The LED lamp of claim 1, wherein the dimmer control unit comprises:

a dimmer type detector configured to receive the input voltage and determine the detected type of dimmer switch;

a phase detector configured to receive the input voltage and determine a detected phase angle modulation of the input voltage representative of the detected dimming amount by comparing the input voltage to one or more threshold voltages that are set differently depending on the detected type of dimmer switch; and

a dimming controller configured to generate the control signals using the detected amount of phase angle modulation to control dimming of the LEDs.

3. The LED lamp of claim 2, wherein the one or more dimmer control signals comprise:

a first control signal indicative of a peak current for driving the LEDs, wherein the peak current is a function of the detected amount of phase angle modulation,

wherein the power converter drives the LEDs in a constant current mode that limits current through the converter to the peak current such that the light intensity of the LEDs is proportional to the detected dimming amount.

4. The LED lamp of claim 2, wherein the dimmer control signals comprise:

a second control signal indicative of a duty cycle for driving the LEDs, wherein the duty cycle is a function of the detected amount of phase angle modulation;

wherein the power converter turns the LEDs on during an on-period of the duty cycle and the power converter turns the LEDs off during an off-period of the duty cycle such that an average light intensity of the LEDs is proportional to the detected dimming amount.

5. The LED lamp of claim 2, wherein the phase detector comprises:

a comparator for comparing the input voltage to a leading threshold to determine a start of a detected on-time, and for comparing the input voltage to a trailing threshold to determine an end of the detected on-time,

wherein the amount of phase angle modulation is determined from the detected on-time, and wherein the leading threshold and the trailing threshold are set based on the detected type of dimmer switch.

6. The LED lamp of claim 5, wherein the leading threshold is a function of a maximum voltage of a previous cycle when the dimmer type detector determines that no dimmer switch is present, and wherein the leading threshold is a fixed value when the dimmer type detector determines that a leading edge dimmer or a falling edge dimmer is detected.

7. The LED lamp of claim 2, wherein the phase detector comprises:

a low-pass filter for filtering the input voltage prior to comparing the input voltage to the leading threshold when the detected type of dimmer switch is a trailing edge dimmer or when no dimmer is present, and wherein the low pass filter is bypassed when the detected type of dimmer switch is a leading edge dimmer.

8. The LED lamp of claim 1, further comprising a chopping circuit configured to dissipate power from the input voltage during a detected off-time of the input voltage, and cycle between dissipating power from the input voltage and providing power from the input voltage to the power converter during a detected on-time of the input voltage.

9. The LED lamp of claim 8, wherein the dimmer control unit further comprises:

a chop generator circuit configured to generate a chopping control signal for controlling switching of the chopping circuit such that the chopping circuit provides power from the input voltage to the power converter during a chopping on-time inversely proportional to the input voltage, and dissipates power from the input voltage during a chopping off-time inversely proportional to the input voltage.

10. The LED lamp of claim 8, wherein the chopping circuit comprises:

a chopping switch;

a chopping inductor coupled in series between the input voltage and the chopping switch, the chopping inductor for storing power from the input voltage when the chopping switch turns on and releasing power when the chopping switch turns off;

a chopping diode coupled in series between the chopping inductor and the power converter, the chopping diode for providing power from the chopping inductor to the power converter when the chopping switch turns off; and

a chopping resistor coupled in series with the chopping switch and the chopping inductor, the chopping resistor for dissipating power from the chopping inductor when the chopping switch turns on.

11. The LED lamp of claim 1, wherein the power converter comprises a flyback power converter.

12. The LED lamp of claim 1, wherein the dimmer control unit determines the detected type of dimmer switch during a configuration stage occurring a fixed number of cycles after startup of the LED lamp.

13. A method for dimming an LED lamp, the method comprising:

receiving a lamp input voltage;

performing a first dimmer detection stage to determine a type of dimmer switch outputting the lamp input voltage;

determining a detecting dimming amount of the lamp input voltage for the detected type of dimmer switch;

determining control signals to drive the LED lamp based on the lamp input voltage and the detected dimming amount; and

driving the LED lamp based on the control signals such that output light intensity of the LED lamp is proportional to the detected dimming amount.

14. The method of claim 13, wherein the first detection stage occurs a fixed number of cycles after startup of the LED lamp.

15. The method of claim 13, wherein performing the first dimmer detection stage comprises:

computing a maximum derivative of the lamp input voltage during a previous cycle of the lamp input voltage;

computing a first threshold value;

determining if the maximum derivative exceeds the first threshold value; and

responsive to the maximum derivative exceeding the first threshold value, determining that the lamp input voltage is outputted from a leading edge dimmer switch.

16. The method of claim 15, further comprising:

computing a second threshold value;

determining a time period during which the lamp input voltage remains below the second threshold value; and

responsive to the time period exceeding a predetermined time threshold, determining that the lamp input voltage is outputted from a trailing edge dimmer switch.

17. The method of claim 16, wherein at least one of the first and second threshold values is a function of a maximum value of the lamp input voltage during a previous cycle of the lamp input voltage.

18. The method of claim 13, further comprising:

performing a second dimmer detection stage a first number of cycles after the first dimmer detection stage;

responsive to the determined dimmer type in the first dimmer detection stage not matching the determined dimmer type in the second dimmer detection stage, performing a third dimmer detection stage a second number of cycles after the second dimmer detection stage;

responsive to the determined dimmer type in the second dimmer detection stage matching the determined dimmer type in the third dimmer detection stage using the determined dimmer type in the second or third detection stage as the detected type of dimmer; and

responsive to the determined dimmer type in the second dimmer detection stage not matching the determined dimmer type in the third dimmer detection stage, outputting a signal indicative of an unsupported dimmer type.

19. The method of claim 13, wherein determining the detected dimming amount comprises:

determining a detected phase angle modulation of the input voltage representative of the detected dimming amount by comparing the input voltage to one or more threshold voltages that are set different depending on the detected type of dimmer switch.

20. The method of claim 19, wherein determining the detected phase angle modulation of the lamp input voltage comprises:

determining a leading threshold and a trailing threshold based at least in part on the detected type of dimmer switch;

comparing the lamp input voltage to the leading threshold to determine a start of a detected on-time of the dimmer switch;

comparing the lamp input voltage to a trailing threshold to determine an end of the detected on-time of the dimmer switch;

determining a period of the input voltage by determining a time between two consecutive starts of the detected on-time; and

determining the phase angle modulation of the lamp input voltage as a ratio of the on-time and the period of the dimmer switch.

21. The method of claim 20, further comprising:

applying a low-pass filter to the lamp input voltage prior to comparing the lamp input voltage to the leading threshold responsive to the detected dimmer type being a trailing edge dimmer or responsive to detecting that no dimmer is present; and

bypassing the low-pass filter responsive to the detected dimmer type being a leading edge dimmer.

22. The method of claim 20, wherein determining the leading threshold comprises:

setting the leading threshold to a function of a maximum voltage of a previous cycle when the dimmer type detector determines that no dimmer switch is present; and

setting the leading threshold to a fixed value when the dimmer type detector determines that a leading edge dimmer or a falling edge dimmer is detected.

23. The method of claim 13, wherein the determining the one or more control signals comprises:

determining a peak current as function of the detected dimming amount, wherein the LED lamp operates in a constant current mode that limits current through the LED lamp to the peak current such that the light intensity of the LED lamp is proportional to the detected dimming amount.

24. The method of claim 13, wherein determining the one or more control signals comprises:

determining a duty cycle as a function of the detected dimming amount, wherein the LED lamp turns on during an on-period of the duty cycle and the LED lamp turns off during an off-period of the duty cycle such that an average output light intensity of the LED lamp is proportional to the detected dimming amount.

25. The method of claim 13, further comprising:

dissipating power from the input voltage during a detected off-time of the input voltage, and cycling between dissipating power from the input voltage and providing power from the input voltage to a power converter of the LED lamp during a detected on-time of the input voltage.

26. The LED lamp of claim 25, wherein cycling between dissipating power from the input voltage and providing power from the input voltage to a power converter comprises:

providing power from the input voltage to the power converter during a chopping on-time inversely proportional to the input voltage; and

dissipating power from the input voltage during a chopping off-time inversely proportional to the input voltage.