LED Current Regulation via Dynamic Sense Resistance
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Solution Overview
Problem
Existing LED driving circuits face challenges in maintaining high current accuracy over a wide range of current changes while keeping a low voltage drop, particularly in applications with limited voltage headroom, such as 1-cell Li-ion powered devices, where the predominant solutions result in significant inaccuracy at low currents due to constant offset voltage errors.
Innovation Solution
The proposed circuit adjusts the current sense resistance using a non-inverting operational amplifier and field effect transistors to regulate LED current, maintaining a constant voltage level at the input terminal while varying the current sense resistance with digital signals, thereby reducing the impact of offset voltage errors across a wide range of currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant current control circuit is used to regulate LED current, then current regulation capability is improved, but voltage drop increases
Solution Approach 1:
The patent implements dynamic current sense resistance adjustment by switching between multiple resistance values based on LED current magnitude. The circuit transitions from a fixed resistance approach to a dynamic one where the sense resistance changes with operating conditions, optimizing both regulation accuracy and voltage drop across different current ranges
Solution Approach 2:
The patent changes the resistance parameter of the current sense resistor from a fixed value to a variable value that adapts to different LED current levels. By switching between different resistance values (e.g., higher resistance for low current, lower resistance for high current), the system maintains accurate regulation while minimizing voltage drop across the sense resistor
2Measurement precision
If offset voltage compensation is increased to improve low current accuracy, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent employs dynamic switching of current sense resistance values based on the magnitude of LED current. By detecting the current range and selecting appropriate resistance values, the system achieves high measurement precision at low currents without requiring complex offset voltage compensation circuits, thereby maintaining relative simplicity
Solution Approach 2:
The patent segments the current regulation range into multiple zones, each with its own optimized sense resistance value. This segmentation allows the circuit to handle different current ranges with appropriate resistance values, improving low current accuracy while keeping the overall circuit design modular and manageable
3Use of energy by moving object
If voltage headroom is reduced to meet battery voltage constraints, then power consumption is improved, but current accuracy deteriorates
Solution Approach 1:
The patent changes the resistance parameter dynamically based on operating conditions. By using higher sense resistance values when LED current is low and lower values when current is high, the system maintains accurate current regulation even with limited voltage headroom, thereby preserving measurement precision while meeting power constraints
Solution Approach 2:
The patent implements a dynamic adaptation mechanism where the current sense resistance automatically adjusts to operating conditions. This dynamic behavior allows the circuit to maintain high current accuracy across different operating points without requiring excessive voltage headroom, thus resolving the conflict between power consumption and accuracy
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 ensures high accuracy and low voltage drop across a wide range of LED currents, reducing percentage errors from 80% at low currents to 8%, thereby overcoming the limitations of prior art circuits.
Implementation Method 1
The non-inverting input voltage of the NOA remains constant while the electrical current passing through the LED is regulated by regulating the current sense resistance means
Implementation Method 2
Each of the driving units comprises a noninverting operational amplifier (NOA) with its input terminal electrically coupled to the third node, a first field effect transistor (FET) with its gate terminal coupled to the NOA's output terminal
Data Source
AI summary
The invention teaches a semiconductor circuit for driving an LED in which the current passing through the LED is regulated by adjusting the NMOS Rdson using a series of digital signals. The circuit maintains a high current accuracy over wide range of current changes while keeping a low voltage drop.