LED Lighting Device Dimming Control via Switching Frequency
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Solution Overview
Problem
Conventional lighting devices using solid-state light emitting elements, such as LEDs, face issues with variation in emission color and light output at low dimming levels due to the DC Dimming Method and Burst Dimming Method, leading to increased flicker and color shift.
Innovation Solution
A lighting device with a switching power circuit and controller that adjusts the average output current by varying the ON and OFF times of the switching element at a predetermined frequency, maintaining a constant intermittent period while adjusting the stopped time based on the dimming level, thereby reducing color and light variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the DC Dimming Method is used to adjust current continuously flowing to LED, then the dimming level can be smoothly controlled, but the emission color of the LED changes in response to magnitude of the current
Solution Approach 1:
The patent applies periodic switching action by turning the switching element on and off at a predetermined switching frequency during intermittent periods. This periodic operation allows the LED to be driven in pulse modes rather than continuous DC, enabling dimming control while maintaining stable emission color by keeping the LED operating point consistent during each pulse.
Solution Approach 2:
The patent dynamically adjusts the duty cycle (ratio of applied time to intermittent period) and switching frequency based on the desired dimming level. By making the driving parameters dynamic rather than static, the system achieves smooth dimming control across different brightness levels while maintaining color stability through consistent pulse-shaped current profiles.
2Illumination intensity
If the Burst Dimming Method is used with periodic switching, then the dimming level can be reduced, but the conducting period shortens and increases variation in the number of switching operations, causing increased variation in amount of light
Solution Approach 1:
The patent changes the switching frequency parameter dynamically based on the dimming level. When the dimming level is reduced and the conducting period shortens, the switching frequency is adjusted to ensure that a substantially constant number of switching operations occur during each applied time. This parameter adaptation maintains light output consistency across different dimming levels.
Solution Approach 2:
The controller monitors the actual number of switching operations during each applied time and adjusts the switching frequency accordingly to maintain a substantially constant number of switching operations. This feedback mechanism ensures that light output variation is minimized even when the conducting period changes with different dimming levels.
3Illumination intensity
If the conducting period is shortened at low dimming levels, then the dimming effect is achieved, but the number of switching operations varies more, increasing light variation
Solution Approach 1:
The system dynamically adjusts the switching frequency in response to changes in the conducting period. When the conducting period is shortened at low dimming levels, the switching frequency is increased proportionally to maintain a constant number of switching operations. This dynamic adaptation allows the system to achieve effective dimming while preventing excessive switching variation that would cause light output instability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution allows for stable light modulation at low dimming levels with reduced variation in emission color and light output, minimizing flicker and maintaining consistent performance across different dimming levels.
Implementation Method 1
a lighting device which activates a light source being a solid-state light emitting element
Implementation Method 2
a solid-state light emitting element such as a light-emitting diode or an organic electroluminescence (EL) element
Implementation Method 3
a switching power circuit for stepping down a DC input voltage to a stepped down DC voltage
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
The controller changes an applied time (ON-time) of a DC voltage while keeping an intermittent period in which the DC voltage is supplied intermittently constant, when adjusting an average value of currents to a predetermined reference value or more, and changes a stopped time (OFF-time) of the DC voltage together with the intermittent period while keeping the applied time constant, when adjusting the average value to a value less than the predetermined reference value. Therefore, the lighting device can reduce variation in emission color compared with the conventional lighting device adopting DC Dimming Method, and can reduce variation in amount of light compared with the case where ON-time is changed until the dimming level reaches a lower limit. As a result, the lighting device can modulate light even at a low dimming level while reducing variation in emission color and variation in amount of light.