AC-Driven LED Boost Circuit for Flicker-Free Operation
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Solution Overview
Problem
Existing solid-state lighting systems using AC-driven LEDs face issues such as visible flickering, reduced power factor, and increased resistive loss due to the requirement of a minimum forward voltage for LEDs, and previous solutions like anti-parallel configurations necessitate twice the number of LEDs for the same luminous flux.
Innovation Solution
A driving circuit comprising a full-wave rectifier, a boost conversion circuit, and a boost control circuit that operates in constant power mode, rectifying AC input voltage to generate a DC output voltage higher than the peak rectified input voltage, maintaining constant power delivery to the LEDs regardless of input voltage variations, and utilizing a current mirror configuration for efficient power distribution between LEDs of different colors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If LEDs are driven using a rectified AC waveform, then the LEDs can be powered from AC input, but the LEDs may turn on for only a part of the rectified AC waveform resulting in visible flickering
Solution Approach 1:
The patent applies continuity of useful action by ensuring LEDs conduct current throughout the entire rectified AC waveform cycle rather than only during portions of the cycle. This is achieved by configuring the LED string to be continuously forward-biased through the full-wave rectifier, eliminating the on/off cycling that causes flicker while maintaining AC input compatibility.
Solution Approach 2:
The patent uses an intermediary approach by introducing a series resistor or current-regulation circuit that acts as a mediator between the rectified AC waveform and the LED string. This intermediary element ensures continuous current flow through the LEDs throughout the entire rectified cycle, preventing flicker while allowing AC operation.
2Ease of operation
If LEDs are driven using a rectified AC waveform, then AC input can be utilized, but the power factor of the system is lowered
Solution Approach 1:
The patent applies parameter changes by modifying the current waveform parameters to match the voltage waveform. By ensuring the LED string conducts throughout the entire rectified cycle and using series resistance to shape the current, the system achieves a power factor close to unity, transforming the poor power factor characteristic of simple rectified AC LED driving into an efficient power delivery system.
3Ease of operation
If LEDs are driven using a rectified AC waveform, then AC power can be supplied, but resistive loss in the system is increased
Solution Approach 1:
The patent reduces resistive loss by optimizing the current waveform parameters. By controlling the LED string to conduct throughout the entire rectified cycle with appropriate current limiting, the system minimizes peak current spikes and maintains smoother current flow, thereby reducing I²R losses in the series resistor and LED string while maintaining AC compatibility.
4Adaptability or versatility
If LEDs are placed in an anti-parallel configuration to be driven on each half-cycle, then AC waveform utilization is improved, but twice as many LEDs are required to produce the same luminous flux
Solution Approach 1:
The patent inverts the conventional approach by instead of using anti-parallel configurations where LEDs are turned on during alternate half-cycles, it configures the LED string to conduct during the entire rectified cycle. This inversion allows a single string of LEDs to produce the required luminous flux without requiring double the number of LEDs, while still fully utilizing the AC waveform through full-wave rectification.
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 maintains a high power factor close to unity, reduces energy loss, and allows for efficient operation with phase-cut dimming, achieving high efficiency and compatibility with existing dimming techniques without additional circuitry, while minimizing the number of LEDs required.
Implementation Method 1
a full wave rectifier configured to rectify an alternating current (AC) input voltage signal to generate a rectified input signal
Implementation Method 2
a boost conversion circuit configured to receive the rectified input signal and deliver power responsively generate a direct current (DC) output voltage signal and to supply the output voltage signal to a solid state light source at a voltage higher than a peak voltage of the rectified input signal
Data Source
AI summary
A driving circuit for a solid state lighting apparatus includes a full wave rectifier configured to rectify an alternating current (AC) input voltage signal to generate a rectified input signal, a boost conversion circuit configured to receive the rectified input signal and responsively generate a direct current (DC) output voltage signal and to supply the output voltage signal to a solid state light source, and a boost control circuit coupled to the boost conversion circuit and configured to cause the boost conversion circuit to operate in a constant power mode.