LED Driving Circuit Current Regulation via Magnetic Coupling
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Solution Overview
Problem
Conventional circuits for driving light sources, such as LED strings, face challenges in accurately controlling the average current due to variations in inductance, input voltage, and voltage across the LED, leading to inconsistent power delivery.
Innovation Solution
A driving circuit with a current sensor and controller that monitors and adjusts the current through an inductor, using a second magnetically coupled inductor for reference and error amplification to maintain a target current level, and incorporates pulse-width modulation and reset signals to control the switch, ensuring accurate current regulation regardless of switch state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional buck converter with current sensing resistor is used, then the circuit structure is simple, but the average current control precision deteriorates due to variations in inductance, input voltage, and LED voltage
Solution Approach 1:
The patent implements a feedback mechanism where the controller continuously monitors the current through the inductor and adjusts the switch timing accordingly. The controller receives feedback signals from the current sensing resistor and modifies the switch on-time to maintain the desired average current level, thereby resolving the contradiction between simple circuit structure and precise current control.
Solution Approach 2:
The patent employs dynamic adjustment of the switch on-time based on real-time current conditions. The controller dynamically modifies the switch operation parameters in response to varying inductance, input voltage, and LED voltage conditions, enabling precise average current control despite changes in circuit components and operating conditions.
2Reliability
If the switch is controlled based on peak current level, then the instantaneous current is regulated, but the average current control precision deteriorates due to variations in inductance and voltage
Solution Approach 1:
The controller uses feedback from the current sensing resistor to continuously monitor and adjust the average current. By incorporating feedback that accounts for variations in inductance and voltage conditions, the system maintains both instantaneous current regulation and precise average current control, resolving the contradiction between these two requirements.
Solution Approach 2:
The patent changes the control parameter from fixed peak current level to dynamically adjusted average current based on real-time monitoring. The controller modifies the switch on-time parameter in response to actual current conditions, enabling precise control of average current while maintaining reliable instantaneous regulation.
3Measurement precision
If a current sensor and error amplifier are added to improve current control precision, then the average current control precision improves, but the device complexity increases
Solution Approach 1:
The controller integrates multiple functions including current sensing, error amplification, PWM generation, and switch control into a single integrated circuit. This multi-functionality approach allows the system to achieve precise average current control through the error amplifier and current sensor while minimizing the increase in overall device complexity by consolidating control functions.
Solution Approach 2:
The error amplifier acts as an intermediary component that processes the feedback signal from the current sensor and generates the appropriate control signal for the PWM generator. This intermediary function enables precise current control by bridging the gap between simple current sensing and complex control requirements, improving precision while managing circuit complexity.
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
The solution enables precise control of the average current flowing through the LED string, maintaining it at a target level with reduced ripple, suitable for high-voltage power sources and improving reliability compared to conventional circuits.
Implementation Method 1
A second inductor magnetically coupled to the first inductor is also electrically coupled to the first inductor via a common node between the switch and the first inductor for providing a reference ground for the controller
Data Source
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AI summary
A driving circuit includes a first inductor coupled in series with a light source for providing power to the light source. A controller coupled to the first inductor can control a switch coupled to the first inductor, thereby controlling a current flowing through the first inductor. A current sensor coupled to the first inductor can provide a first signal indicative of the current flowing through the first inductor, regardless of whether the switch is on or off. The switch is controlled according to the first signal. A second inductor magnetically coupled to the first inductor is also electrically coupled to the first inductor via a common node between the switch and the first inductor for providing a reference ground for the controller. The reference ground is different from the ground of the driving circuit.