Active Capacitor Circuit for LED Driver Ripple Reduction
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Solution Overview
Problem
Existing LED driver solutions compromise on efficiency, power density, lifetime, and cost, often requiring bulky capacitors to maintain high power factor and low harmonic distortion, while causing significant 100/120 Hz ripple and flicker, especially with modern power LEDs.
Innovation Solution
An active capacitor circuit with a control unit and low frequency capacitor, integrated into the load or used in parallel, which operates as a compact, high-order-low-pass filter, eliminating AC components and allowing for modularity and plug-and-play functionality without requiring load current measurement or signal connection to the power stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If large electrolytic capacitors are used in parallel with LED loads to maintain high power factor and low harmonic distortion, then power factor is improved, but device size and weight increase significantly
Solution Approach 1:
The patent replaces passive electrolytic capacitors with an active power stage that uses electronic switching (MOSFETs/IGBTs) and control circuitry to perform power factor correction. This substitution eliminates the need for large bulk capacitors while achieving the same power factor improvement through active power conversion rather than passive energy storage.
Solution Approach 2:
The invention changes the operating parameters by using high-frequency switching (typically 20-100 kHz) instead of line-frequency operation. This allows the use of much smaller magnetic components and capacitors while achieving equivalent or superior power factor correction performance through pulsed power conversion.
2Object-affected harmful factors
If large filter capacitors are used to reduce 100/120 Hz ripple, then ripple is reduced, but device complexity and cost increase
Solution Approach 1:
The patent replaces passive RC or LC filter circuits with an active power stage that uses PWM control and synchronous rectification to eliminate ripple. The active switching circuitry dynamically compensates for ripple currents rather than relying on large passive filter components, reducing both size and complexity.
Solution Approach 2:
The invention implements feedback control where the output voltage and current are continuously monitored and used to adjust the switching duty cycle. This closed-loop control actively maintains constant output power and eliminates ripple without requiring large filter capacitors, as the control system dynamically compensates for variations.
3Device complexity
If single-stage converter architecture is used to reduce component count, then device complexity is reduced, but power factor and harmonic distortion performance deteriorate
Solution Approach 1:
The patent designs a single power stage that performs multiple functions simultaneously: rectification, power factor correction, voltage regulation, and ripple elimination. By integrating these functions into one unified circuit topology with a single switching node, the invention achieves two-stage performance without two-stage complexity, maintaining high power factor while using fewer components.
Solution Approach 2:
The invention uses dynamic switching control where the duty cycle is continuously adjusted based on instantaneous input voltage and output load conditions. This dynamic operation allows the single-stage converter to maintain optimal power factor across varying line conditions and load levels, matching the performance of traditional two-stage designs with fixed operating points.
4Stability of the object's composition
If conventional LED driver circuits are used to maintain constant output power, then power stability is improved, but 100/120 Hz ripple and flicker increase
Solution Approach 1:
The patent ensures continuous power delivery to the LED load by using high-frequency switching that operates many cycles per line period. The output capacitor is kept continuously charged through high-frequency rectification, eliminating the pulsating power delivery that causes 100/120 Hz flicker while maintaining constant average output power.
Solution Approach 2:
The invention uses periodic high-frequency switching pulses synchronized to deliver energy continuously to the output. By operating at frequencies much higher than the line frequency (20-100 kHz versus 50/60 Hz), the system creates many small energy transfer cycles that average out to constant power delivery, eliminating visible flicker while maintaining power stability.
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 active capacitor circuit effectively reduces 100/120 Hz ripple and flicker to less than 1%, enhances reliability, and allows for high switching frequencies, eliminating the need for large electrolytic capacitors and improving LED driver performance.
Implementation Method 1
an output power stage coupled between said coupling terminals for converting said periodic current into said drive current
Implementation Method 2
a low frequency capacitor coupled between a capacitor output terminal of said output power stage and a coupling terminal
Implementation Method 3
a control unit for controlling said output power stage by use of a control signal obtained from a feedback of the drive voltage, a capacitor voltage across said low frequency capacitor and/or a capacitor current through said low frequency capacitor
Data Source
AI summary
The present invention relates to an active capacitor circuit (40) for use in a driver device for driving a load (22), in particular an LED unit comprising one or more LEDs (23). Further, the present invention relates to a driver device comprising such an active capacitor circuit. The proposed active capacitor circuit comprises coupling terminals (41, 42) for providing a drive voltage (vD) and/or drive current (iD) for driving a load (22) to be coupled between said coupling terminals (41, 42), an output power stage (50) coupled between said coupling terminals (41, 42) for converting said periodic current (iA) into said drive current (iD), a low frequency capacitor (46) coupled between a capacitor output terminal (48) of said output power stage (50) and a coupling terminal (42), and a control unit (60) for controlling said output power stage (50) by use of a control signal (Sd) obtained from a feedback of the drive voltage (vD), a capacitor voltage (vC) across said low frequency capacitor (46) and/or a capacitor current (iC) through said low frequency capacitor (46).