LED String Circuit with Dual Current Sources for Efficiency
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Solution Overview
Problem
Existing LED driving circuits face efficiency challenges due to narrow operating ranges and high costs, particularly when accommodating voltage changes caused by aging or temperature fluctuations, and often require complex and expensive solutions such as multiple shunt transistors or switching power supplies.
Innovation Solution
A circuit arrangement featuring two current sources connected to a series of LEDs, with switching means to adjust between them based on sensed voltage drops, allowing for optimal efficiency across a wide operating range by selectively bypassing LEDs and adjusting current levels, and incorporating a microcontroller for simplified and cost-effective control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a linear power supply is used to provide constant current to LED string, then the LED string can be operated with constant current, but the efficiency can only be maintained at a very narrow operating point and cannot accommodate voltage changes due to ageing or temperature
Solution Approach 1:
The patent applies dynamics by making the circuit configuration adaptable through switching between different states. The operating point is dynamically adjusted by switching between Series mode (full LED string active) and Parallel mode (bypass transistor active) based on detected voltage conditions, allowing the system to maintain optimal efficiency across a wide operating range rather than being fixed at a narrow operating point
Solution Approach 2:
The patent changes the operational parameters of the circuit by detecting voltage drops across the LED string and current source, and switching between different circuit configurations based on these parameter changes. When voltage changes due to ageing or temperature occur, the system detects these parameter changes and transitions between operating modes to maintain efficiency
2Reliability
If the operating point is set close to regular operation conditions to counteract voltage changes, then voltage changes can be accommodated within a narrow range, but efficiency is reduced
Solution Approach 1:
Rather than statically setting the operating point to accommodate voltage changes at the cost of efficiency, the patent dynamically switches between two operating modes: Series mode for normal operation with high efficiency, and Parallel mode when voltage changes occur. This dynamic approach maintains high efficiency while accommodating voltage variations through timely mode transitions
3Loss of energy
If switching power supplies are used to achieve high efficiency and wide operating range, then efficiency and adaptability are improved, but the cost increases significantly
Solution Approach 1:
The patent segments the LED string into two controllable groups: the main LED string and a bypass LED substring. By controlling current distribution between these segments through switching, the system achieves adaptive operation without requiring a complex switching power supply. The bypass segment can be activated to adjust the operating point when voltage changes occur
Solution Approach 2:
The patent achieves parameter adaptation through simple switching between predefined circuit states rather than complex continuous regulation. The system monitors voltage parameters and switches between Series and Parallel configurations, providing wide operating range and high efficiency without the complexity of switching power supply circuits
4Reliability
If individual LEDs are shunted using field effect transistors to return to operating range, then the operating point can be maintained, but the device complexity and cost increase as each LED requires a shunt transistor
Solution Approach 1:
Instead of segmenting each individual LED with its own shunt transistor, the patent segments the LED string at a higher level into the main string and a bypass substring. A single bypass transistor controls the entire bypass substring, dramatically reducing component count while maintaining the ability to adjust operating characteristics when voltage changes occur
Solution Approach 2:
The patent merges the control function for multiple LEDs into a single bypass transistor that controls a substring of LEDs. This consolidation maintains operating point stability through voltage-dependent switching while reducing device complexity by combining what would otherwise require multiple individual control elements
Data Source
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AI summary
A Circuit arrangement (1) for an LED module (53) comprising a plurality of serially connected LEDs (11-25), comprises a first current source (35) and a second current source (36). The first current source (35) is serially connected to all the LEDs (11 - 25) of the LED module (53). The second current source (36) is serially connected to a first sub-set (33) of LEDs (11 - 24) of the LED module (53). The LEDs (11 - 24) of the first sub-set (33) are serially connected. The first sub-set (33) comprises at least one LED (25) less than the LED module (53).