LED Backlight Control Circuit for Accurate Open-Short Detection
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Solution Overview
Problem
Existing LED backlight systems face difficulties in accurately detecting and distinguishing between open-circuit and short-circuit conditions in LED strings due to voltage changes, which can trigger false protection mechanisms and are not applicable to directly powered systems, and small sensing resistor values can lead to incorrect determinations, especially at low currents.
Innovation Solution
An LED control circuit with N switching circuits and N abnormality detecting circuits that detect voltage or current at the first end of each LED string, determining abnormal states by measuring impedance when the voltage or current is below a threshold, allowing for precise identification of open-circuit or short-circuit conditions without relying on load changes in the system voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the system voltage is raised by adjusting the on time of the switch in the boost unit, then the abnormal conditions can be detected, but the cross-voltage between two ends of the LED strings becomes larger which may accidentally trigger other protection mechanisms
Solution Approach 1:
The patent introduces a sensing resistor as an intermediary component to detect the voltage across the switch. By measuring the voltage drop across this intermediary resistor, the system can detect abnormal conditions without directly raising the system voltage, thus avoiding false triggers of protection mechanisms while maintaining accurate detection capability
Solution Approach 2:
The patent changes the detection parameter from system voltage level to switch voltage level (across the sensing resistor). This parameter change allows detection of abnormal conditions through current variations reflected in the switch voltage, avoiding the need to raise system voltage and preventing false triggers while maintaining detection accuracy
2Device complexity
If a sensing resistor with small resistance value is used, then the hardware complexity is reduced, but it causes a failure to correctly determine that the LED strings are short-circuited to the ground terminal
Solution Approach 1:
The patent employs feedback by continuously monitoring the voltage across the sensing resistor and comparing it against reference values. This feedback mechanism allows the system to correctly identify short-circuit conditions even with small resistance values, as the feedback loop can detect the characteristic voltage patterns that indicate short-circuits without requiring large resistance values
Solution Approach 2:
The patent substitutes the traditional mechanical/current-based detection method with an electrical voltage measurement approach across the sensing resistor. By measuring voltage instead of directly measuring current or using mechanical switches, the system achieves accurate short-circuit detection with minimal hardware complexity
3Use of energy by moving object
If the current of the LED strings is set to be a low current, then the power consumption is reduced, but the LED strings are lightly loaded for the boost unit so that it is difficult to distinguish the abnormal conditions according to whether the load of the boost unit becomes light or not
Solution Approach 1:
The sensing resistor serves as an intermediary that amplifies the detection signal. Even at low currents, the voltage drop across the sensing resistor provides sufficient signal level for accurate detection of abnormal conditions, allowing the system to maintain low power consumption while preserving the ability to distinguish between different abnormal states
Solution Approach 2:
The patent changes the detection parameter from boost unit load level to switch voltage level. This parameter change enables accurate detection of abnormal conditions at low currents, as the switch voltage reflects the LED string status directly without requiring high load levels that would increase power consumption
Data Source
AI summary
An LED backlight system and an LED control circuit are provided. The LED backlight system includes an LED string and the LED control circuit. The LED control circuit includes an LED driver, a switching circuit and an abnormality detecting circuit. The LED driver is configured to generate a control signal. The switching circuit controls a current flowing through the LED string in response to the control signal. The abnormality detecting circuit is configured to detect a voltage or the current of a first end of the LED string. When the voltage or the current of the first end of the LED string is less than or equal to a threshold value, the abnormality detecting circuit turns off the switching circuit, and the abnormality detecting circuit detects an impedance of the first end of the LED string to determine an abnormal state of the LED string.