Primary Side LED Current Control via Resonant Converter
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Solution Overview
Problem
Existing LED converters using LLC resonant converters often require secondary side measurements and control circuits, leading to increased costs and complexity due to the need for galvanic barrier feedback, and the peak control principle results in inaccurate LED current control due to changing relations between resonant converter current and LED current.
Innovation Solution
An LED converter that operates by measuring and controlling the primary side resonant converter current using integral parameters such as root mean square (RMS), averaged full-wave rectified, or averaged half-wave rectified values, eliminating the need for secondary side measurements and feedback across the galvanic barrier, and employing a primary side control circuit to adjust the switching frequency based on low-pass filtered signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If secondary side measurements and control circuits are used, then LED current control accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the measurement function from the secondary side to the primary side by measuring the resonant converter current Iprim through the inductivity Lm. This eliminates the need for secondary side measurement circuits and feedback paths across the galvanic barrier, reducing device complexity while maintaining control capability through primary side integral parameter measurement
Solution Approach 2:
The patent uses the primary side resonant converter current Iprim as an intermediary parameter to control the LED current ILED. By measuring Iprim and its integral parameters (RMS, averaged rectified values) on the primary side, the system indirectly controls the secondary side LED current without direct secondary side measurement, simplifying the overall control architecture
2Measurement precision
If secondary side feedback is implemented, then LED current control precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent removes the feedback path across the galvanic barrier by extracting the measurement function to the primary side. This eliminates the need for optocouplers and secondary side control circuits, reducing component count and manufacturing cost while maintaining control precision through primary side integral parameter measurement
Solution Approach 2:
The patent creates a control loop on the primary side that copies the essential control function without requiring physical feedback from the secondary side. By measuring integral parameters of the primary current and using them for frequency control, the system achieves the same control objective with fewer components
3Ease of operation
If peak control principle is used, then control simplicity is improved, but measurement precision deteriorates
Solution Approach 1:
The patent changes the control parameter from peak current to integral parameters (RMS, averaged full-wave rectified, or averaged half-wave rectified values) of the resonant converter current. This parameter transformation provides a more accurate correlation with LED current while maintaining the simplicity of frequency-based control through the low-pass filtered signal
4Device complexity
If primary side control is implemented, then device complexity is reduced, but measurement precision may deteriorate
Solution Approach 1:
The patent transforms the primary side current measurement into integral parameters (RMS, averaged rectified values) that have a more accurate correlation with the secondary side LED current. This parameter transformation compensates for the lack of direct secondary side measurement, maintaining precision while simplifying the control circuit to primary side only
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
This approach simplifies the design, reduces costs by eliminating secondary side components, and provides more accurate control of the LED current by correlating primary side electric parameters with LED current and voltage, while maintaining safety through the absence of secondary side feedback, thus improving the efficiency and reliability of the LED converter.
Implementation Method 1
A LLC converter is a resonant half-bridge converter that uses two inductors (LL) and a capacitor (C), known as an LLC configuration
Implementation Method 2
A transformer connected to or being part of the resonant converter then transfers power over a galvanic barrier
Data Source
Figure 1~2
Figure 3~4
AI summary
In a first aspect the invention provides an LED converter for providing power to a LED string comprising at least one LED, comprising a resonant converter with a switching regulator, preferably a clocked half-bride converter, a galvanic barrier, the primary side of which being supplied by the switching regulator and the secondary side of which being arranged for providing directly or indirectly power to the LED string, a control circuit on the primary side of the galvanic barrier and which is adapted to sense an averaged value of an primary side electric parameter indicative, of a current supplied to the LED string on the secondary side of the galvanic barrier and wherein the control circuit is adapted to control a switching frequency of switching regulator switches, in particular switches of the clocked half-bridge, based on the sensed averaged value of the primary side electric parameter to control the current supplied to the LED string, wherein the control circuit preferably receives no feedback signal from the secondary side of the galvanic barrier.