LED Converter Primary-Side Current Sensing
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Solution Overview
Problem
Existing LED converter systems require a potential separation across a galvanic isolation barrier for current feedback, which complicates the control of LED current and increases costs due to the need for components like optocouplers.
Innovation Solution
The LED current is determined by relating the LED voltage, electrical power, and power losses in the circuitry, using differential current sensing on the primary side of the isolated switched resonant stage, allowing for indirect detection of the LED current via the current on the primary side of the transformer, eliminating the need for secondary-side detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If secondary-side detection of LED current is used to provide accurate feedback, then measurement precision is improved, but device complexity increases due to potential separation requirements and optocouplers
Solution Approach 1:
The patent uses the transformer as an intermediary element to transfer current information from the secondary side to the primary side without direct electrical connection. By sensing the current through the transformer winding and using it as a mediator to derive LED current information on the primary side, the system achieves accurate measurement without requiring complex secondary-side feedback circuits with optocouplers
Solution Approach 2:
Instead of measuring LED current directly on the secondary side and feeding it back to the primary side control circuit, the patent inverts the approach by measuring the current on the primary side and deriving the LED current information from it. This inversion eliminates the need for secondary-side detection and potential separation, reducing device complexity while maintaining measurement accuracy
2Device complexity
If indirect current detection via primary side is used, then device complexity is reduced, but measurement precision deteriorates due to power losses in circuitry
Solution Approach 1:
The patent implements a feedback mechanism where the sensed primary current is continuously monitored and used to regulate the LED current. By establishing a relationship between primary current and LED current through the transformer turns ratio and power balance equations, the system compensates for power losses and maintains precise LED current control through feedback regulation
Solution Approach 2:
The patent changes the measurement parameter from direct LED current on the secondary side to primary current on the primary side. By transforming the measurement location and using parameter relationships (current ratio based on transformer turns ratio, power balance considering losses), the system achieves accurate indirect measurement that accounts for circuit power losses
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 and cost-reduces the current sensing for LED converters by eliminating the need for secondary-side detection, enabling efficient and cost-effective control of the LED current through frequency modulation and duty cycle control.
Implementation Method 1
an isolated resonant, e.g. LLC, LCC etc., converter is responsible for transferring power over a galvanic barrier from a primary side to a secondary side
Implementation Method 2
switched resonant circuit, such as an isolated LLC converter
Data Source
Figure 1
Figure 2
Figure 2a
AI summary
The invention relates to a LED converter (100), comprising: - an isolated switched resonant stage (LLC) supplying terminals for driving an LED load (106), wherein an LED current iLED is feedback-controlled based on feedback- control signals preferably all sensed at a primary side stage (102) of an isolation stage of the isolated switched resonant stage; - a control unit (108) controlling at least one switch (S1, S2) of the switched resonant stage on the basis of the feedback-control signals supplied to the control unit (108), wherein said feedback-control signals comprise: a.) a signal representing the voltage across the LED load VLED; b) a signal indicating a DC supply voltage of the primary side VBUS; and c.) at least one signal representing the current sensed at the primary side and representing the current flowing on the primary side of the isolation stage of isolated switched resonant stage.