Cold Cathode Tube Lighting Current Control Circuit
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Solution Overview
Problem
Conventional cold cathode tube lighting systems face challenges in maintaining constant tube current and luminance when using the both-side high-voltage driving method, particularly in long or small-diameter tubes, due to high impedance issues and the inability to detect current accurately with existing current detecting circuits.
Innovation Solution
A cold cathode tube lighting device that uses ballast elements with separately-excited or self-excited inverters to apply driving pulses with different phases to both sides of the tubes, incorporating a tube current controlling unit to detect and adjust the current flowing through each tube to a specified value, ensuring constant luminance, and includes temperature and voltage monitoring for accuracy and safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a both-side high-voltage driving method is used to prevent luminance gradient in long cold cathode tubes, then luminance uniformity is improved, but current detection becomes impossible with conventional resistor circuits due to high voltage
Solution Approach 1:
The patent introduces a current detection circuit that operates at low voltage level by detecting current through the ballast element rather than directly at the high-voltage tube terminals. The detection circuit uses the ballast element as an intermediary to measure current indirectly, avoiding the need for high-voltage resistant components while maintaining accurate current measurement capability
Solution Approach 2:
The patent replaces the conventional direct electrical measurement method (using resistors at high voltage) with an indirect measurement approach that substitutes the measurement location to a safe, low-voltage point in the circuit, thereby eliminating the need for specialized high-voltage measurement components
2Illumination intensity
If driving pulses are applied to both sides of the cold cathode tube with different phases, then luminance gradient is prevented, but control of tube current becomes complex
Solution Approach 1:
The patent implements a feedback control mechanism where the detected tube current is fed back to the driving circuit to adjust the driving pulses. This automatic feedback loop simplifies the control complexity by allowing the system to self-regulate the tube current based on actual measurements, eliminating the need for complex manual control mechanisms
Solution Approach 2:
The system performs self-regulation of tube current through the feedback mechanism, where the control circuit automatically adjusts driving parameters based on detected current values, reducing the need for external intervention or complex control algorithms
3Device complexity
If conventional current detecting circuits are used in both-side high-voltage driving, then circuit simplicity is maintained, but accurate current detection and luminance control become impossible
Solution Approach 1:
The patent uses the ballast element as an intermediary component that enables current detection at low voltage levels. By measuring current through the ballast element rather than directly at the high-voltage tube terminals, the system maintains circuit simplicity while achieving accurate current detection capability
Solution Approach 2:
The patent substitutes the measurement location from the high-voltage region to the low-voltage region, replacing the need for complex high-voltage measurement systems with simple low-voltage detection circuits that can accurately measure tube current through the ballast element
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 effectively maintains constant luminance across multiple cold cathode tubes by accurately controlling tube current through each ballast element, reducing the need for high-voltage components and preventing excessive voltage issues, thereby enhancing the efficiency and reliability of the lighting system.
Implementation Method 1
voltage-reducing coils and temperature detection for precise control
Implementation Method 2
ballast elements with separately-excited or self-excited inverters to apply driving pulses
Data Source
AI summary
A cold cathode tube lighting device is provided which is capable of achieving stable luminance when driven by applying driving pulses to input terminals on both sides of each of two or more cold cathode tubes. Each of currents flowing through coils in each of coil units on both sides of each of two or more cold cathode tubes is detected by voltage detecting sections and a tube current flowing through each of the cold cathode tubes based on a value obtained by adding each of the currents using an adder and a duty ratio of each of driving pulses is controlled so that the tube current becomes a specified current value to keep the luminance of the cold cathode tubes constant.