SSL Driver Controller Synchronizes Mains Frequency to Eliminate Flicker
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Solution Overview
Problem
Solid state lighting (SSL) devices like LEDs and OLEDs experience visible flicker due to the sinusoidal AC mains voltage, which falls below the required minimum voltage, causing the devices to switch off at frequencies of 100/120 Hz, resulting in an annoying flicker effect.
Innovation Solution
A controller for the driver circuit of SSL devices synchronizes with the mains frequency to determine pulse intervals at a frequency greater than the perceptual frequency of light intensity variations, ensuring the input voltage within these intervals is above a pre-determined minimum, thereby generating a drive voltage that maintains the SSL device's on-voltage and reduces flicker by operating the device in a pulsed mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the SSL device is driven directly from AC mains voltage, then the device can operate continuously, but the device experiences visible flicker at 100/120 Hz due to the sinusoidal waveform falling below the minimum on-voltage
Solution Approach 1:
The patent applies periodic pulsed action by driving the SSL device with pulses having a frequency greater than the perceptual frequency (e.g., >400 Hz). This transforms the continuous driving approach into periodic pulsed driving, which eliminates visible flicker while maintaining effective illumination through the persistence of vision effect.
Solution Approach 2:
The patent changes the frequency parameter of the driving signal from the mains frequency (50/60 Hz) to a higher frequency (>400 Hz) that exceeds the human eye's perceptual frequency. This parameter change transforms the harmful low-frequency flicker into imperceptible high-frequency pulsing.
2Reliability
If the power converter operates at maximum voltage step-up conversion ratio, then the device can operate during low input voltage periods, but the duty cycle increases leading to higher power loss
Solution Approach 1:
The patent dynamically adjusts the operating parameters of the power converter by synchronizing pulse generation with the instantaneous input voltage waveform. The controller activates pulses only when the instantaneous input voltage exceeds the threshold, creating a dynamic on/off pattern that adapts to voltage variations and avoids continuous high-duty-cycle operation.
Solution Approach 2:
The patent uses preliminary voltage threshold detection to determine when to activate pulse driving. By detecting when the instantaneous input voltage exceeds the threshold (Von/n), the system prepares and triggers pulses at optimal moments, ensuring reliable SSL device operation during favorable voltage conditions while minimizing unnecessary operation during low voltage periods.
3Object-affected harmful factors
If the controller uses pulse intervals above perceptual frequency, then the flicker becomes imperceptible, but the control complexity increases due to synchronization requirements
Solution Approach 1:
The patent implements feedback by continuously monitoring the instantaneous input voltage and using this information to control pulse generation. The controller detects the voltage waveform and synchronizes pulse activation with voltage peaks, creating a closed-loop control system that automatically adapts to voltage variations without requiring complex external synchronization circuits.
Data Source
AI summary
This disclosure relates to illumination systems. In particular it relates to a method and system for avoiding flicker (in particular 100 Hz or 120 Hz flicker) in solid state lighting devices such as LED or OLED assemblies. A controller for a driver circuit of a solid state lighting device (SSL) is described. The driver circuit comprises a power converter to convert a varying input voltage into a drive voltage for the SSL device. The input voltage is derived from a rectified AC mains voltage and frequency. The power converter is used with a maximum voltage step-up conversion ratio. The controller synchronizes to the mains frequency and determines a plurality of pulse intervals repeated at a pulse frequency where the pulse frequency is greater than a perceptual frequency of light intensity variations perceivable by a human eye.