Lighting Driver Shunt Control for Stable Low Dimming
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Solution Overview
Problem
Existing solid state lighting drivers for tubular LED lamps face challenges in maintaining stable control signals at low dimming levels, particularly when connected to fluorescent ballasts, as the detection signal can intermittently disappear, leading to unstable closed-loop control.
Innovation Solution
A lighting driver system that generates a detection signal through two mechanisms: analyzing the voltage at the driver input and autonomously correcting for time delays when the input voltage is not detected, ensuring continuous synchronization and preventing asynchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the shunt device is operated for a large portion of the cycle to achieve low dimming levels, then the light output is reduced to the desired low level, but the detection signal disappears intermittently causing unstable closed-loop control
Solution Approach 1:
The correction circuit generates a detection signal in advance based on the shunt control signal timing, before the actual voltage detection can occur. This preliminary generation of the detection signal ensures that the control loop receives the necessary synchronization signal even when the voltage detection fails due to large shunt operation duration.
Solution Approach 2:
The correction circuit acts as an intermediary that bridges the gap between the shunt control signal and the detection signal. When the voltage detection circuit fails to generate a detection signal, the correction circuit intervenes by generating a corrected detection signal based on the known timing relationship between the shunt control signal and the expected detection signal.
2Device complexity
If the detection signal is generated solely by analyzing voltage at the driver input, then the system is simple, but the detection signal disappears when the input voltage is not detected due to large shunt duration
Solution Approach 1:
The correction circuit generates the detection signal in advance based on the shunt control signal timing, before the actual voltage detection can occur. This preliminary generation ensures continuous detection signal availability even when voltage detection fails.
Solution Approach 2:
The correction circuit uses feedback from the shunt control signal to generate the detection signal. The timing relationship between the shunt control signal and the detection signal is maintained through this feedback mechanism, ensuring synchronization even when direct voltage detection fails.
3Reliability
If hysteresis control is used to maintain stable operation, then the control loop is stable, but audible noise is generated at certain frequencies
Solution Approach 1:
The system adjusts the hysteresis control parameters dynamically to change the operating frequency away from audible noise frequencies. By modifying the hysteresis width or switching frequency parameters, the system maintains stability while moving the operational frequency to regions that are either inaudible or less perceptible.
Data Source
AI summary
A lighting driver is for receiving an alternating current power supply from a fluorescent lighting ballast. A shunt device is provided for selectively shunting the power supply to implement dimming control. A detector is provided for generating a detection signal and for providing the detection signal to the control circuit to operate the shunt device. The detector has a detection circuit for analyzing a voltage at the driver input and generating 5 the detection signal accordingly, when the voltage is detected. In addition, for situations where the voltage detection does not correctly generate the detection signal, a correction circuit generates the detection signal for a time delay from the end of operating the shunt device. This prevents control stability problems at low dimming levels.