Switchable Bypass Capacitors for Deep-Dimming LED Drivers
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Solution Overview
Problem
Existing LED lighting systems experience significant color shift and flicker during deep dimming due to the use of amplitude modulation, which is undesirable for applications requiring stable color temperature and low flicker.
Innovation Solution
A lighting unit with parallel capacitors and switches that dynamically control current flow through LED loads, transitioning between modes to minimize color shift and flicker by disconnecting capacitors during deep dimming and operating switches in a linear mode to maintain stable current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If amplitude modulation is used to reduce LED current for deep dimming, then light output is reduced, but color temperature shifts significantly
Solution Approach 1:
The patent applies dynamics by making the capacitor connection state changeable based on operating conditions. The switch dynamically connects or disconnects the capacitor from the LED string depending on whether the system is in dimming mode or full brightness mode, allowing the circuit topology to adapt to different operating requirements and resolve the contradiction between dimming capability and color stability.
2Stability of the object's composition
If PWM modulation is used at deep dimming levels to maintain color stability, then color temperature remains stable, but flicker increases
Solution Approach 1:
The capacitor acts as an intermediary energy storage element that smooths the PWM current pulses. By storing energy during conducting phases and releasing it during non-conducting phases, the capacitor filters the PWM ripple and reduces flicker, allowing PWM dimming to be used at deep dimming levels without the harmful flicker effect while maintaining color stability.
3Object-generated harmful factors
If a capacitor is connected in parallel with LED load to smooth current, then flicker is reduced, but modulation depth of PWM current decreases
Solution Approach 1:
The switch dynamically controls the capacitor connection to the LED load based on the dimming level. At deep dimming levels where PWM is used, the capacitor is connected to provide current smoothing and reduce flicker. At full brightness or intermediate levels where amplitude modulation is used, the capacitor is disconnected to avoid reducing the modulation depth. This dynamic switching resolves the contradiction between flicker reduction and PWM effectiveness.
Data Source
AI summary
The invention relates to a lighting unit comprising a power converter for providing a regulated power to a first LED load where the first LED load comprises at least one LED, wherein the first LED load is coupled to the power converter, a series combination of a first capacitor and a first switch coupled in series with each other, wherein the series combination is coupled in parallel with the LED load, wherein the power converter is arranged to operate in a first mode, provide a first amount of the regulated power to the first LED load, and wherein the first switch is closed, and in a second mode, provide a second amount of the regulated power to the first LED load, wherein the second amount of the regulated power to the first LED load is lower than the first amount of the regulated power to the first LED load, and wherein the first switch is opened.