CCFL Driving Apparatus Abnormality Detection Circuit
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Solution Overview
Problem
Existing fluorescent lamp driving circuits face difficulties in accurately detecting circuit abnormalities, especially when high-voltage probes are used, as the feedback voltage fluctuations make it challenging to determine whether the fluctuations are due to a failure or the probe itself.
Innovation Solution
A fluorescent lamp driving apparatus that includes two inverters outputting AC voltages of reversed phases to a U-shaped CCFL, with current-voltage converting circuits generating detection voltages and an abnormality detection circuit that determines circuit abnormalities based on the potential difference between these voltages, allowing for accurate detection regardless of the high-voltage probe's presence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-voltage probe is used to test voltage across the CCFL, then voltage measurement is enabled, but the feedback voltage fluctuates making abnormality detection difficult
Solution Approach 1:
The patent segments the abnormality detection function into two independent detection methods: (1) feedback voltage-based detection for normal operation, and (2) detection voltage difference-based detection for probe-connected states. This segmentation allows each method to operate independently based on system state, resolving the contradiction between measurement capability and detection accuracy.
Solution Approach 2:
The patent changes the detection parameter based on system state: when no probe is connected, it uses feedback voltage magnitude; when a probe is connected, it switches to comparing the voltage difference between two detection voltages. This parameter change allows accurate abnormality detection regardless of probe connection status.
2Reliability
If feedback voltage is monitored for abnormality detection, then circuit protection is enabled, but the detection becomes unreliable when high-voltage probe is connected
Solution Approach 1:
The patent introduces an intermediary detection mechanism using two current-voltage converting circuits that convert transformer secondary currents to detection voltages. By comparing the difference between these intermediary detection voltages rather than directly monitoring feedback voltage, the system achieves reliable abnormality detection even when high-voltage probes are connected, as the probe's capacitive effect does not significantly impact this differential measurement.
3Adaptability or versatility
If two inverters are used to drive U-shaped CCFL, then reversed phase AC voltages are achieved, but the detection circuit complexity increases
Solution Approach 1:
The patent merges the detection functions of both inverters into a unified abnormality detection system. By comparing the voltage difference between the two current-voltage converting circuits, the system simultaneously monitors both inverter outputs using a single detection circuit architecture, reducing overall complexity while maintaining full monitoring capability for U-shaped CCFL operation.
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
Enables reliable detection of circuit abnormalities, including open or low voltage conditions, even when a high-voltage probe is used, ensuring proper operation and protection of the CCFL.
Implementation Method 1
a first current-voltage converting circuit which converts a secondary current of a transformer in the first inverter to a voltage and outputs the voltage as a first detection voltage
Data Source
AI summary
In an apparatus for driving a CCFL, a first inverter outputs a first alternating current (AC) voltage to one end of the CCFL. A second inverter outputs a second AC voltage having a reversed phase to the first AC voltage to the other end of the CCFL. A first current-voltage converting circuit converts a secondary current of a first transformer in the first inverter to a voltage and outputs the voltage as a first detection voltage. A second current-voltage converting circuit converts a secondary current of a second transformer in the second inverter to a voltage and outputs the voltage as a second detection voltage. A first abnormality detection circuit determines a circuit abnormality when the potential difference between the first and second detection voltages exceeds a predetermined first threshold voltage.