LED Driver Circuit With Switched Capacitor Flicker Suppression
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Solution Overview
Problem
Conventional LED driver circuits face challenges in eliminating flicker caused by low-frequency ripple in mains power, leading to poor reliability and high costs due to the need for high-capacity constant-current loops and large input capacitors, which also result in degraded power factor and harmonic rejection performance.
Innovation Solution
A novel LED driver circuit design that uses a rectifier bridge set, a capacitive branch with an input capacitor, and a load branch with a constant-current controller, where the input capacitor supplies power only when the mains voltage is below a turn-on threshold, and the rectified mains power supplies directly when voltage exceeds this threshold, allowing for power source switching and reducing ripple and harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the capacitance of the input capacitor is increased to suppress low-frequency ripple and eliminate flicker, then flicker is reduced, but current distortion at the input terminal increases, degrading power factor and failing to meet sub-harmonic requirements
Solution Approach 1:
The patent applies dynamics by making the input capacitor's connection state variable - it is dynamically connected and disconnected based on voltage comparison. The control circuit continuously monitors the voltage across the input capacitor and compares it with the rectified mains voltage, switching the capacitor's connection state accordingly. This dynamic operation allows the capacitor to suppress ripple during appropriate periods while avoiding continuous connection that would cause current distortion and poor power factor.
2Object-generated harmful factors
If a constant-current loop is added to control charging current for the input capacitor to reduce current distortion, then sub-harmonic performance is enhanced, but the current capacity requirement increases, making the design costly and complex
Solution Approach 1:
The patent uses the rectified mains voltage as an intermediary control signal. Instead of implementing a complex constant-current loop, the control circuit simply compares the voltage across the input capacitor with the rectified mains voltage and uses this comparison to control the switching of the capacitor's connection. This intermediary voltage comparison approach achieves current distortion reduction without requiring high current capacity or complex control circuits.
3Object-generated harmful factors
If the input capacitor is not directly connected to the input terminal to reduce current distortion, then sub-harmonic requirements are met, but the design has high input impedance and cannot absorb high voltage after rectifying mains power, reducing reliability
Solution Approach 1:
The patent applies preliminary anti-action by proactively controlling the input capacitor's connection state before voltage spikes or surges can damage the circuit. The control circuit continuously monitors voltages and disconnects the input capacitor from the rectified mains power output when voltage levels become dangerous, preventing voltage spikes from reaching and damaging downstream components. This preliminary protective action enhances reliability while maintaining the benefit of reduced current distortion.
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 design effectively eliminates flicker, improves input current harmonic rejection, reduces the need for high-capacity components, and enhances reliability while meeting environmental standards, resulting in a simpler, cost-effective, and more reliable LED driver circuit.
Implementation Method 1
a rectifier bridge set configured to receive and rectify the mains power and to output the rectified mains power
Implementation Method 2
a capacitive branch connected between one set of output terminals of the rectifier bridge set, wherein the capacitive branch at least comprises an input capacitor
Data Source
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AI summary
An LED driver circuit is used to drive an LED load and to mitigate flicker caused by ripple from mains power. The driver circuit includes: a rectifier bridge set for rectifying the mains power and having at least one set of output terminals; a load branch being capable to be coupled into two different current paths, the load branch including an LED load and LED constant-current controller; and a capacitive branch at least including an input capacitor. With a turn-on voltage of the load branch being taken as a threshold, one of the rectified mains power and the input capacitor is selected as a power source for the load branch. This LED driver circuit is simple in structure, highly reliable and capable of flicker elimination, and has optimized input current harmonic rejection performance that can meet the requirements of various relevant standards.