LED Driver Current Sensing via Switching Transistor
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Solution Overview
Problem
Existing LED systems require expensive high-side current sense amplifiers or transformers and optical couplers to measure current in high voltage DC or AC applications, which increases costs and complexity, especially in isolated topologies.
Innovation Solution
The system senses current through a switching transistor and uses a relationship between the switching transistor current and LED current to derive the LED current, eliminating the need for high-side current sense components and optical couplers by measuring on the low-current side, applicable to both isolated and non-isolated topologies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-side current sense amplifiers or transformers are used to measure LED current in high voltage applications, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent introduces an intermediary switching transistor through which a scaled-down version of the LED current flows. This transistor acts as a mediator that allows indirect measurement of the high current LED string by measuring the lower current through the switch, eliminating the need for expensive high-side current sense amplifiers or transformers while maintaining measurement accuracy through the known current relationship.
Solution Approach 2:
The patent creates a simplified copy of the current measurement path by routing a portion of the LED current through the switching transistor. Instead of directly measuring the full LED current with complex high-voltage components, the system measures a scaled copy of the current signal that contains the same regulatory information but can be measured with simple, low-cost components.
2Reliability
If optical couplers are used in isolated topologies to transfer LED current information, then reliability is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the current measurement function from the high-voltage isolated side and relocates it to the low-voltage switching side. By measuring the current through the switching transistor on the primary side, the system eliminates the need for optical couplers or other isolation barriers to transfer current information, thereby reducing complexity while maintaining reliability through direct measurement.
3Measurement precision
If expensive high current sensing components are employed, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive, delicate high-current sensing components with inexpensive switching transistors that are already necessary for the power conversion function. The switching transistor serves dual purposes: power switching and current sensing, eliminating the need for separate expensive sensing components and significantly reducing manufacturing cost while maintaining adequate measurement precision for current regulation.
Data Source
AI summary
Embodiments of the present invention provide a system and method for determining a magnitude of current driving LEDs by sensing a current through a switching transistor and extracting the information of the LED current based on a relationship between the current through the switching transistor and the current driving the LEDs.