LED Light Source Phase Cut Dimmer Compatibility
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Solution Overview
Problem
Existing LED light sources are incompatible with phase cut dimmers, limiting their use in homes and office buildings, as they are either non-dimmable or only dimmable over a limited range with specific dimmer types.
Innovation Solution
A compact LED light source design that includes a rectifier, control means, a switchable bleeder current source, a latch, a unidirectional element, and a clamp circuit, allowing it to be compatible with phase cut dimmers by controlling current flow independently of the dimmer's phase angle and preventing current zero-crossing issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If LED light sources are designed to be compact and directly connectable to AC supply, then device simplicity and compactness are improved, but compatibility with phase cut dimmers deteriorates
Solution Approach 1:
The patent introduces a bleeder current source as an intermediary component that mediates between the simple AC-connected LED circuit and the phase cut dimmer. This bleeder current source provides a continuous current path through the dimmer, enabling compatibility without requiring complex circuitry in the LED light source itself. The intermediary handles the dimmer interaction requirements separately from the LED driving circuitry.
2Device complexity
If LED loads are controlled by periodical DC voltage amplitude variations, then compact design is achieved, but dimming control precision deteriorates
Solution Approach 1:
The patent segments the control function by separating the LED current control from the dimmer phase angle control. The control means divides the AC period into distinct phases: utilizing the bleeder current source during the dimmer's off-phase and transitioning to direct LED current control during the on-phase. This segmentation allows independent optimization of each control aspect.
Solution Approach 2:
The patent implements dynamic switching between different current sources based on the dimmer's phase angle. The control means dynamically transitions between using the bleeder current source and directly controlling LED current, adapting the control strategy to the instantaneous dimmer state. This dynamic approach enables precise dimming control across the full range.
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
Enables the LED light source to be dimmed with a wide range of phase cut dimmers, including both leading edge and trailing edge types, achieving high power factor in undimmed operation and low dim levels in dimmed operation without the need for additional circuitry in each light source.
Implementation Method 1
a rectifier equipped with a first input terminal and a second input terminal for coupling to output terminals of the phase cut dimmer, supplying an AC supply voltage
Implementation Method 2
a series arrangement comprising N LED loads
Implementation Method 3
LED loads comprising series arrangements and possibly parallel arrangements of individual LEDs
Data Source
AI summary
A LED light source comprises—a full bridge rectifier equipped with a first input terminal and a second input terminal for coupling to output terminals of the phase cut dimmer, —a series arrangement comprising N LED loads, a first and second end of said series arrangement being coupled to a first output terminal and a second output terminal of the full bridge rectifier respectively, —control means for during a period of the rectified AC supply voltage subsequently making the LED loads comprised in the first series arrangement carry a current, one by one and in dependency of the momentary amplitude of the rectified AC supply voltage when the momentary amplitude increases and for subsequently making the LED loads stop carrying a current, one by one, and in dependency of the momentary amplitude of the rectified AC supply voltage when the momentary amplitude decreases, said control means controlling the current through the LED loads at zero when the output voltage of the phase cut dimmer equals zero and controlling the current through the LED loads at a value that is independent from the phase angle of the phase cut dimmer when the output voltage of the phase cut dimmer differs from zero Volt. In order to make the LED light source compatible with a phase cut dimmer, the LED light source is further equipped with—a switchable bleeder current source coupled between the first and second output terminal of the full bridge rectifier, —a latch coupled between the first and second output terminals of the full rectifier bridge and comprising a series arrangement of a resistor and a capacitor to prevent the current through the dimmer from crossing zero after a leading edge generated by the phase cut dimmer, in case the phase cut dimmer is a leading edge phase cut dimmer, —a unidirectional element arranged in series with the capacitor for preventing discharging of the capacitor via the LED loads or the adjustable bleeder current source, and—a clamp circuit coupled to the capacitor and comprising a current source for discharging the capacitor and providing a low ohmic path for the dimmer current when the dimmer is off.