LED PWM Pulse Shaping for Low-Flicker Dimming Control
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Solution Overview
Problem
Existing LED dimming techniques, such as PWM and intensity control, face challenges in providing a wide range of light intensity levels without perceivable flickering and complexity in LED driver design, especially at low light intensity levels.
Innovation Solution
A driver apparatus with a pulse shaping portion that generates a dimming control signal based on a PWM signal with a lower frequency, using a capacitor and a second switch to control charge provision, resulting in an average driving current that is a smaller portion of the maximum current level than indicated by the duty cycle, with softened rising edges to reduce flickering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If PWM dimming is used to control light intensity, then light intensity control is achieved, but perceivable flickering occurs at low duty cycles
Solution Approach 1:
The patent uses PWM (Pulse Width Modulation) technique to control LED light intensity by applying periodic switching signals. The duty cycle of the PWM signal determines the average current and thus the light intensity. This periodic action allows continuous dimming control while keeping the LED driver operating at fixed frequency, avoiding the need for variable frequency operation.
Solution Approach 2:
The patent introduces a pulse shaping circuit that pre-processes the PWM signal before it reaches the LED driver. The pulse shaping circuit generates extended pulses with softened rising edges, which are then fed to the LED driver. This preliminary signal conditioning ensures that the LED current rises smoothly, reducing perceivable flickering at low duty cycles while maintaining accurate dimming control.
2Illumination intensity
If intensity dimming is used to provide low light intensity levels, then accurate light intensity control is achieved, but the LED driver must be able to provide adjustable output current levels
Solution Approach 1:
The patent separates the dimming control function into two independent parts: the PWM signal generation (which can be implemented in any LED driver) and the pulse shaping circuit (which processes the PWM signal). This segmentation allows the LED driver to maintain its fixed-frequency switching operation while the pulse shaping circuit provides the additional dimming control functionality, making the solution compatible with various LED driver types.
Solution Approach 2:
The pulse shaping circuit acts as an intermediary between the PWM controller and the LED driver. It receives the standard PWM signal, processes it by extending pulse widths and softening rising edges, and then provides the modified signal to the LED driver. This intermediary approach enables enhanced dimming performance without requiring modifications to the core LED driver architecture, improving compatibility across different driver designs.
3Object-affected harmful factors
If PWM frequency is increased to reduce perceivable flickering, then flickering is reduced, but the switching losses in the power converter increase
Solution Approach 1:
The pulse shaping circuit performs preliminary signal processing by extending the PWM pulses and softening their rising edges before they reach the power converter. This preprocessing allows the use of lower switching frequencies while still achieving smooth current transitions and reducing perceivable flickering. The extended pulses ensure that the LED current has sufficient time to rise and fall smoothly, maintaining low flicker perception without requiring high switching frequencies that would increase switching losses.
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
This approach enables straightforward control of light intensity with reduced perceivable flickering at low light levels and avoids the complexity of hybrid dimming, while maintaining performance equivalent to hybrid dimming in terms of flicker reduction and intensity adjustment.
Implementation Method 1
The pulse shaping portion comprises a capacitor configured to receive a charging current and a second switch connected in parallel with the capacitor
Implementation Method 2
a switched-mode power converter entity for converting operating power supplied to the apparatus into the driving current
Data Source
Figure 1a~1b
Figure 2~6a
Figure 4~6b
AI summary
An apparatus for providing a driving current for one or more light emitting diodes is provided. The apparatus comprises a power converter portion for converting operating power supplied to the apparatus into the driving current in accordance with a driving signal, a driving portion for controlling provision of the driving current from the power converter portion in accordance with the voltage of a dimming control signal, and a pulse shaping portion for generating the dimming control signal on basis of a PWM signal, the pulse shaping portion comprising a capacitor configured to receive a charging current and a switch connected in parallel with the capacitor, the switch arranged to control provision of the charge from the capacitor as the dimming control signal in accordance with the PWM signal, the pulse shaping portion thereby arranged to derive pulses of the dimming control signal on basis of the PWM signal such that rise time in the pulses of the dimming control signal is longer than that of the pulses of the PWM signal.