Primary-Side Resonant LED Converter With Zero-Crossing Extrapolation
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Solution Overview
Problem
Existing resonant converters for LED loads face challenges in achieving accurate output current control while maintaining cost-efficiency due to the need for expensive components like current measuring coils and complex phase relation determination.
Innovation Solution
A primary side switched resonant converter with a control circuit that modulates HF switching operations using LF PWM pulses with variable duty cycle, detects falling zero crossings using a shunt resistor, and calculates rising zero crossings through extrapolation, ensuring accurate output current control and reduced complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current measuring coil is used for zero crossing detection, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses a shunt resistor to create an electrical copy of the current waveform instead of directly measuring with a current measuring coil. The voltage across the shunt resistor replicates the current information, allowing zero crossing detection without the complexity and cost of specialized current sensing components.
Solution Approach 2:
The patent replaces the mechanical/electromagnetic current measuring coil with an electrical substitution method using a shunt resistor and voltage measurement. This substitution eliminates the need for complex magnetic coupling and current transformation mechanisms while achieving the same detection function.
2Manufacturing precision
If phase relation determination is implemented, then output current control precision is improved, but device complexity increases
Solution Approach 1:
The control circuit determines phase relation autonomously by comparing the PWM signal phase with the resonant current phase detected through the shunt resistor. This self-determination mechanism eliminates the need for external phase measurement devices or complex synchronization circuits, achieving precise control while maintaining simplicity.
3Loss of energy
If resonant frequency operation is used, then energy efficiency is improved, but output current control flexibility deteriorates
Solution Approach 1:
The patent implements feedback control where the control circuit continuously monitors the resonant current phase and adjusts the PWM duty cycle accordingly. This feedback mechanism allows the converter to maintain resonant operation for efficiency while dynamically adapting the output current level to match dimming requirements, resolving the conflict between energy efficiency and control flexibility.
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 provides high cost-efficiency and accurate output current control by simplifying the detection and calculation of zero crossings, reducing complexity and costs.
Implementation Method 1
Resonant converters are preferably operated with a frequency close to their resonant frequency
Implementation Method 2
power transmission between the primary converter side and the secondary converter side
Implementation Method 3
A change of output current or voltage is performed by modulating high frequency pulses of the resonant converter with a low frequency pulse width modulation PWM signal
Data Source
Figure 1
Figure 2
AI summary
An isolated, primary side switched resonant converter (100) for supplying an LED load (34) is provided. Said converter (100) comprises an isolation barrier defining a primary side (61) and a secondary side (62), a control circuit arranged for varying the power transmitted by the converter (100) by modulating HF switching operations, preferably with constant frequencies, of at least primary side switch (11, 12) of the converter (100) with LF PWM pulses with variable duty cycle, and means for detecting (24) the falling zero crossing of a current through a primary side resonance circuit of the converter (100). In this context, the converter (100) is void of means for detecting the rising zero crossings of the current through the primary side resonance circuit of the converter (100). In addition to this, the control circuit is arranged to control the trailing high/low transition of each PWM pulse to be during one of the rising/falling zero crossings.