Backlight Control Circuit Using Two Transistors for Multi-Backlight Protection
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Solution Overview
Problem
The existing backlight control circuits for LCDs are costly due to the high number of transistors required to protect multiple backlights, especially when the number of backlights is large, as each additional backlight necessitates additional transistors to function properly.
Innovation Solution
A backlight control circuit design that uses only two transistors to protect multiple backlights by incorporating a switching circuit and an input circuit with diodes, resistors, and capacitors, which reduces the overall cost and complexity by eliminating the need for additional transistors with increasing numbers of backlights.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional transistors are used to protect each backlight, then the reliability of backlight protection is improved, but the device complexity and cost increase
Solution Approach 1:
The patent merges the protection functions for multiple backlights into a single transistor circuit. Instead of using separate transistors for each backlight, the invention combines all protection functions into one transistor that monitors the collective status of all backlights through their inspecting circuits, thereby reducing the number of transistors from multiple to just one while maintaining protection reliability.
Solution Approach 2:
The single transistor in the invention serves a universal protection function for all backlights simultaneously. The transistor is designed to respond to any fault condition (open circuit or short circuit) in any backlight through the inspecting circuits, making it a multi-functional protection element that replaces multiple dedicated transistors.
2Reliability
If additional transistors are used for each backlight, then the backlight protection capability is improved, but the manufacturing cost increases
Solution Approach 1:
The invention combines multiple protection functions into a single transistor, directly reducing the bill of materials and assembly complexity. This merging approach reduces manufacturing cost by eliminating the need to source, test, and assemble multiple transistors while maintaining the same protection capability across all backlights.
Solution Approach 2:
The universal transistor design provides cost-effective protection by using a single component to perform what previously required multiple components. This multi-functional approach reduces both component cost and assembly cost, making the backlight system more economical to manufacture while maintaining full protection capability.
3Device complexity
If a simple circuit design is used, then the device complexity is reduced, but the ability to protect multiple backlights is compromised
Solution Approach 1:
The invention achieves multi-backlight protection with a simple circuit by designing the single transistor and its inspecting circuits to universally monitor all backlights. The circuit topology allows any backlight fault to be detected through the common inspecting circuit, providing versatile protection without increasing circuit complexity.
Solution Approach 2:
The inspecting circuits automatically detect backlight faults and trigger the protection transistor without requiring complex control logic. The circuit uses the inherent electrical characteristics of the backlights (current flow patterns) to self-diagnose faults, eliminating the need for complex monitoring systems while maintaining multi-backlight protection capability.
Data Source
AI summary
An exemplary backlight control circuit (20) includes: at least two load circuits (210), a pulse width modulation integrated circuit (PWM IC) (250) having a current sampling pin (251), a switching circuit (270), and an input circuit (230). Each load circuit includes a backlight and a backlight inspecting circuit having an output end. The switching circuit includes a first transistor which includes a source electrode connected to ground, a drain electrode connected to the current sampling pin, a gate electrode connected to a power supply. The input circuit includes at least two first diodes, at least two input resistor, a second transistor, and a pink-to-pink detector circuit. The pink-to-pink detector circuit includes a second diode, a second bias resistor, and a second filter capacitor. Each output end of the load circuits is connected to the gate electrode of the second transistor via the input resistor, the first and second diode.