Primary-Side LED Current Detection Circuit
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Solution Overview
Problem
Existing driver circuits for LED lighting systems require detection circuits on the secondary side and bridging elements to detect current, leading to high costs and complex circuit arrangements, and are prone to detection errors due to 'reverse current' issues, especially at high temperatures.
Innovation Solution
A driver circuit with a potential-separated converter on the primary side, featuring a detection circuit with a transformer and an active detection rectifier, allowing current detection on the primary side and minimizing errors by using an active rectifier and RC circuit to handle AC voltage and parasitic reverse currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a detection circuit is provided on the secondary side with a bridging element to detect current, then current detection is achieved, but circuit costs and complexity increase
Solution Approach 1:
The patent inverts the conventional approach by moving the detection circuit from the secondary side to the primary side of the converter. The current through the light source is detected indirectly by measuring parameters on the primary side and calculating the secondary current based on the known transformer ratio, eliminating the need for secondary-side detection components and bridging elements.
Solution Approach 2:
The patent introduces an intermediary calculation approach where the primary current measurement serves as a mediator to determine the secondary current. By measuring the primary current and using the transformer turns ratio as an intermediary factor, the system derives the secondary current without direct measurement on the secondary side.
2Loss of information
If a bridging element is used to bridge the barrier for current detection, then current information can be transmitted across the barrier, but circuit costs increase
Solution Approach 1:
The patent extracts the bridging element from the circuit by performing all current measurements on the primary side. The galvanic barrier is maintained without requiring any bridging components, as the primary current measurement and subsequent calculations provide all necessary information without crossing the barrier.
3Device complexity
If passive detection rectifier is used, then circuit simplicity is maintained, but detection errors occur due to reverse current at high temperatures
Solution Approach 1:
The patent inverts the problematic configuration by placing the detection circuit on the primary side where reverse current issues do not occur. The active rectifier is used on the primary side to ensure accurate detection without the temperature-dependent reverse current problems that plague passive rectifiers on the secondary side.
Solution Approach 2:
The patent converts the potential harm of using active rectifiers (which are more complex than passive ones) into a benefit by eliminating reverse current errors. The additional complexity of the active rectifier is justified by the significant improvement in detection accuracy, especially at high temperatures where passive rectifiers fail.
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
Enables accurate detection of LED current on the primary side, reducing detection errors and circuit complexity while maintaining reliability across temperature variations.
Implementation Method 1
A sensing circuit for indirectly sensing the current on the secondary side of the converter comprises a transformer with at least one primary-side winding on the secondary side of the converter
Implementation Method 2
detection circuit with a transformer and an active detection rectifier, allowing current detection on the primary side
Data Source
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AI summary
The invention relates to a drive circuit for operating an illuminant, preferably at least one LED, comprising an isolated converter which is clocked on the primary side by a control unit by means of at least one controlled switch unit, said converter supplying a rectifier starting from which the illuminant can be fed, a measurement circuit for indirectly measuring the current on the secondary side of the converter having a transformer with at least one winding on the primary side.