LED Load Control Circuit With Burst Mode for Smooth Dimming
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Solution Overview
Problem
Traditional dimming techniques for LED light sources result in perceptible changes in light intensity, especially at low intensity levels, making fine-tuning of light output challenging.
Innovation Solution
A load control device with a control circuit that adjusts the operating period of an inverter circuit by varying the on-time and duty cycle of drive signals, employing a burst mode to regulate load current, ensuring smooth intensity transitions by maintaining a minimum on-time and using closed-loop control for precise current regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If traditional dimming techniques (PWM or CCR) are used to reduce LED light intensity, then the light output can be dimmed, but perceptible changes in light intensity occur especially at low intensity levels
Solution Approach 1:
The patent employs pulse-width modulation (PWM) technique where a pulsed signal with varying duty cycle is supplied to the LED light source. The LED is driven in periodic bursts rather than continuous operation, allowing precise control of average current while maintaining minimum on-time to avoid perceptible flicker and achieve smooth intensity transitions especially at low light levels.
Solution Approach 2:
The control circuit adjusts multiple parameters including duty cycle, frequency, and minimum on-time of the pulsed signal to the LED driver. By dynamically changing these parameters based on desired intensity level, the system achieves smooth dimming without perceptible steps or flicker, resolving the contradiction between dimming capability and transition smoothness.
2Illumination intensity
If the on-time of the inverter circuit is reduced to achieve lower average current, then the average load current decreases, but the on-time may become too short to maintain proper operation
Solution Approach 1:
The control circuit dynamically adjusts the on-time parameter to maintain a minimum threshold value regardless of the desired dimming level. This dynamic parameter adjustment ensures that the inverter circuit always operates within its reliable range while still achieving the desired average current reduction through duty cycle control, resolving the contradiction between low current operation and minimum on-time requirements.
3Illumination intensity
If burst mode operation is implemented to fine-tune low-end intensity, then smooth transitions at low intensities are achieved, but the control circuit complexity increases
Solution Approach 1:
The patent implements closed-loop feedback control where the control circuit continuously monitors the actual LED current and adjusts the pulsed signal parameters accordingly. This feedback mechanism enables automatic fine-tuning of low-end intensity levels without requiring complex manual control, achieving smooth transitions while keeping the control circuit design practical and manageable.
Data Source
AI summary
A load control device for an electrical load is configured to operate in a normal mode and a burst mode to adjust the amount of power delivered to the electrical load. The load control device comprises a control circuit that operates in the normal mode to regulate an average magnitude of a load current conducted through the load between a maximum rated current and a minimum rated current. During the normal mode, the control circuit controls the operating period of a load regulation circuit between a high-end operating period and a low-end operating period. The control circuit operates in the burst mode to regulate the average magnitude of the load current below the minimum rated current. During the burst mode, the control circuit adjusts the low-end operating period to be less than or equal to a minimum on time of the load regulation circuit.