LED Driver Pin Reduction via Base Voltage Sensing
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Solution Overview
Problem
Conventional liquid crystal displays require three pins for each LED channel to detect shorts and protect against overcurrent, leading to increased costs due to the higher number of pins in the device configuration.
Innovation Solution
A liquid crystal display configuration using transistors with collector electrodes connected to LED cathodes and emitter electrodes connected to monitor resistors, with an LED driver having two pins per channel to supply driving signals and detect shorts by monitoring base electrode voltages, allowing for reduced pin count and overcurrent protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If three pins are used for each LED channel to detect shorts and protect against overcurrent, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent makes the first pin (base electrode pin) perform multiple functions: it supplies driving signals to the transistor base and simultaneously senses voltage changes to detect LED shorts. This multi-functionality eliminates the need for a separate sensing pin, reducing the total pin count from three to two per LED channel while maintaining short detection capability
Solution Approach 2:
The patent combines the driving signal supply function and the short detection sensing function into a single pin (the base electrode pin). By merging these two functions that were previously performed by separate pins, the device achieves the same reliability protection with fewer pins, thereby reducing device complexity
2Reliability
If three pins are used for each LED channel, then short detection capability is improved, but manufacturing cost increases
Solution Approach 1:
The first pin serving dual purposes as both a driving signal output and a sensing input for short detection reduces the total pin count required. This reduction directly lowers manufacturing costs by decreasing the number of pins that need to be manufactured, packaged, and connected in the final device assembly
3Reliability
If base electrode voltage is monitored to detect LED shorts, then overcurrent protection is improved, but device complexity increases
Solution Approach 1:
The system uses the existing base electrode voltage signal to detect LED shorts without requiring additional monitoring circuits or components. The voltage change at the base electrode naturally indicates LED status, and this self-indicating property is exploited for protection, avoiding the need for complex external monitoring mechanisms
Data Source
AI summary
A liquid crystal display comprises: a liquid crystal panel; LED strings connected to an output terminal of a DC power source and providing light to the liquid crystal panel; transistors whose collector electrodes are connected to cathodes of LEDs positioned at the lowermost stages of the LED strings, and whose emitter electrodes are connected to monitor resistors; and an LED driver which has first pins respectively connected to base electrodes of the transistors to supply driving signals and second pins connected between the emitter electrodes of the transistors and monitor resistors, wherein the first pins sense voltages of the base electrodes of the transistors to detect a short in an LED, wherein the LED driver comprises driving signal supply portions for supplying the driving signal and short sensing portions for detecting the presence or absence of a short in the LED.