Adaptive PWM Frequency Control for LED Health and Reliability
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Solution Overview
Problem
Current PWM-controlled LED drivers face limitations in increasing PWM pulse instantaneous frequency due to parasitic capacitances and non-ideal edge shapes, leading to non-linear light intensity distortion and difficulty in diagnosis at low luminous intensities, with existing methods reducing PWM resolution or requiring high clock frequencies.
Innovation Solution
Implementing an adaptive PWM pulse instantaneous frequency method that adjusts PWM period and duty cycle based on light intensity, allowing for higher PWM frequencies at high intensities and lower frequencies at low intensities to minimize edge influence and facilitate diagnosis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If PWM pulse instantaneous frequency is increased above 100 Hz to avoid flickering, then flickering is reduced, but health risks according to IEEE 1789-2015 increase and the minimum current source active time becomes too short (nanosecond range) for proper LED driving due to parasitic capacitances
Solution Approach 1:
The patent applies dynamics by making the PWM frequency adaptive rather than fixed. The control device adjusts the PWM pulse instantaneous frequency dynamically based on the desired light intensity: using lower frequencies (100-2000 Hz) for higher intensities where health risks are more critical, and higher frequencies for lower intensities where flicker is less noticeable. This dynamic adaptation resolves the contradiction between avoiding flicker and minimizing health risks.
Solution Approach 2:
The patent changes the parameter of PWM frequency based on operating conditions. Instead of using a single high frequency that causes health issues, the system varies the frequency parameter according to the duty cycle requirements, selecting appropriate frequency ranges to balance flicker avoidance with health safety guidelines from IEEE 1789-2015.
2Measurement precision
If PWM pulse duration is shortened to achieve higher PWM frequencies, then PWM resolution is improved, but diagnostic capability deteriorates due to insufficient time for stable current and voltage measurements
Solution Approach 1:
The system dynamically adjusts PWM pulse duration based on operational mode. During normal operation, shorter pulses provide sufficient resolution. During diagnostic modes, the control device extends PWM pulse duration to allow stable current and voltage measurements, thereby maintaining both resolution and diagnostic capability through dynamic adaptation.
Solution Approach 2:
The patent incorporates periodic diagnostic intervals where PWM operation is temporarily modified. During these periodic diagnostic phases, the system uses extended pulse durations to enable accurate measurements, while maintaining high-resolution PWM control during normal lighting operation, thus resolving the contradiction between resolution and diagnostics.
3Object-affected harmful factors
If PWM pulse instantaneous frequency is increased to 2000 Hz or above as recommended by IEEE 1789-2015, then health risks are minimized, but the PWM period becomes too short allowing insufficient time for stable current source activation and proper LED driving
Solution Approach 1:
The control device dynamically selects PWM frequency based on reliability requirements. For applications requiring high reliability and stable LED operation, the system uses lower frequencies (100-2000 Hz) that provide sufficient pulse duration for proper current source activation and LED driving. This dynamic selection ensures reliable operation while still considering health guidelines.
4Speed
If fixed high PWM frequency is used to minimize flicker, then flicker is avoided, but light intensity distortion increases due to non-ideal edge shapes and parasitic capacitances at low luminous intensities
Solution Approach 1:
The system dynamically adjusts PWM frequency based on the desired light intensity level. For low luminous intensities where edge effects and parasitic capacitances cause significant distortion, the control device uses lower frequencies that provide longer pulse durations, reducing the relative impact of edge effects. For higher intensities, higher frequencies can be used where the distortion becomes less significant, thus maintaining light intensity accuracy across different brightness levels.
Data Source
AI summary
A control signal for controlling a light emitting device is PWM modulated in time, the PWM modulation comprising PWM pulses and PWM periods. The PWM pulse instantaneous frequency of a PWM pulse is the reciprocal of the instantaneous PWM period of the PWM pulse. The PWM pulse instantaneous frequency depends on the PWM duty cycle of the PWM pulses of the control signal. The PWM pulse instantaneous frequency of the PWM pulses is a first PWM pulse instantaneous frequency at a first PWM duty cycle of the control signal, and is a second PWM pulse instantaneous frequency at a second PWM duty cycle of the control signal. In an operating condition, the first PWM duty cycle is less than the second PWM duty cycle and the first PWM pulse instantaneous frequency is less than the second PWM pulse instantaneous frequency.