SSL Driver Circuit PWM Dimming Synchronization
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Solution Overview
Problem
Solid State Lighting (SSL) devices, such as LED-based light bulbs, often exhibit visible flicker, especially at low dimming levels, due to inadequate control of driver circuits over AC mains voltage and dimming levels, which affects the consistency and quality of the light emitted.
Innovation Solution
A driver circuit with a controller that operates a power converter using a combination of continuous and PWM modes to manage energy transfer from AC mains voltage to SSL devices, ensuring flicker-free operation by synchronizing PWM pulses with AC mains voltage and adjusting energy levels based on dimming thresholds, utilizing a power switch and inductor to store and release energy effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If PWM dimming is used to reduce power consumption at low dimming levels, then energy efficiency is improved, but visible flicker occurs due to insufficient energy transfer consistency
Solution Approach 1:
The patent applies periodic action by using PWM (Pulse Width Modulation) to periodically switch the power converter between active energy transfer mode and standby mode. At low dimming levels, the converter operates in discrete PWM cycles rather than continuously, reducing average power consumption while maintaining sufficient energy transfer during active periods to prevent visible flicker. The periodic activation ensures consistent light output during each pulse while minimizing overall energy usage.
Solution Approach 2:
The patent implements dynamics by making the power converter's operating mode adaptive based on dimming level requirements. The controller dynamically switches between continuous operation mode (for high dimming levels where consistent energy transfer is critical) and PWM periodic operation mode (for low dimming levels where energy efficiency is prioritized). This dynamic adaptation allows the system to optimize the balance between energy efficiency and light output consistency according to actual operating conditions.
2Stability of the object's composition
If continuous operation mode is used to maintain stable light output, then illumination consistency is improved, but energy consumption increases at low dimming levels
Solution Approach 1:
The patent applies periodic action by using PWM (Pulse Width Modulation) to periodically switch the power converter between active energy transfer mode and standby mode. At low dimming levels, the converter operates in discrete PWM cycles rather than continuously, reducing average power consumption while maintaining sufficient energy transfer during active periods to prevent visible flicker. The periodic activation ensures consistent light output during each pulse while minimizing overall energy usage.
Solution Approach 2:
The patent implements dynamics by making the power converter's operating mode adaptive based on dimming level requirements. The controller dynamically switches between continuous operation mode (for high dimming levels where consistent energy transfer is critical) and PWM periodic operation mode (for low dimming levels where energy efficiency is prioritized). This dynamic adaptation allows the system to optimize the balance between energy efficiency and light output consistency according to actual operating conditions.
3Use of energy by moving object
If PWM frequency is reduced to improve energy efficiency, then power consumption decreases, but flicker becomes more visible to the human eye
Solution Approach 1:
The patent applies parameter changes by carefully selecting and maintaining the PWM frequency within an optimal range (typically above 100Hz or synchronized with mains frequency) that balances energy efficiency with flicker imperceptibility. The controller adjusts PWM parameters such as duty cycle and timing to ensure that even at reduced frequencies, the light output remains above the human visual detection threshold. This parameter optimization allows the system to reduce power consumption while preventing visible flicker.
Solution Approach 2:
The patent applies continuity of useful action by ensuring that PWM pulses are timed and synchronized to maintain continuous perceptible light output. The controller coordinates PWM switching with the mains voltage cycle and ensures sufficient pulse duration and overlap to maintain steady illumination perception. This continuous action approach ensures that energy efficiency gains from PWM do not result in perceptible interruptions or flicker in the light output.
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
The solution ensures flicker-free operation of SSL devices at both high and low dimming levels by maintaining consistent energy transfer and minimizing visible light fluctuations, providing stable illumination without the perception of flicker to the human eye.
Implementation Method 1
a power converter (305) configured to transfer energy from an input of the driver circuit (300) to the SSL device (309). The power converter (305) may comprise an inductor (307) configured to store energy from the input of the driver circuit (300) and release the stored energy towards the SSL device (309)
Implementation Method 2
a power switch (202) which may be configured to enable an inductor current through the inductor (307), when the power switch (202) is in on-state. The power switch (202) may be put into on-state to store energy within the inductor (307), and the power switch (202) may be put into off-state to release the energy towards the SSL device (309)
Implementation Method 3
The sequence of PWM pulses may be synchronized with the AC mains voltage. By way of example, the position of the sequence of PWM pulses may be maintained unchanged from one half-wave to a next half-wave, or from one full-wave to a next full-wave of the AC mains voltage
Data Source
Figure 1
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Figure 2b
AI summary
The present document relates to driver circuits for solid state lighting (SSL) devices. In particular, the present document relates to driver circuits which are configured to reduce or remove flicker of SSL devices, notably at relatively low dimming levels. A controller (306) for a driver circuit (300) of a solid state lighting (SSL) device (309) is described. The driver circuit (300) comprises a power converter (305) configured to transfer energy from an input of the driver circuit (300) to the SSL device (309). The energy at the input is derived from an AC mains voltage at a mains frequency. The controller (306) is configured to determine a dim level for the SSL device (309). Furthermore, the controller (306) is configured to operate the power converter (305) continuously in a first operation mode for supplying energy to the SSL device (309) at a first energy level, if the dim level is above a pre-determined dim level threshold. In addition, the controller (306) is configured to operate the power converter (305) in the first operation mode at a time duration of PWM pulses (517), and operate the power converter (305) in a second operation mode at a time duration in-between the PWM pulses (517), if the dim level is below the pre-determined dim level threshold. In the second operation mode, the power converter (305) is operated for supplying energy to the SSL device (309) at a second energy level; wherein the second energy level is lower than the first energy level. The PWM pulses (517) are synchronized with the AC mains voltage.