LED Backlight Driving Circuit PWM Dimming Protection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing PWM dimming method for LED backlight driving circuits in LCDs can damage the constant current driving chip due to high voltage output when the dimming signal is low, leading to reliability and lifespan issues.
Innovation Solution
Incorporating a controllable switch unit in series with the power supply and constant current driving chip, which turns off before the adjusting dimming unit to prevent high voltage exposure, ensuring the constant current driving chip is not damaged by the large voltage output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a typical PWM dimming method is used to control LED backlight brightness, then the brightness can be adjusted by changing duty cycle, but the constant current driving chip may be damaged by high voltage output when the dimming signal is low
Solution Approach 1:
The controllable switch unit is configured to turn off before the adjusting dimming unit when receiving a low-level PWM signal. This preliminary action prevents the high voltage from reaching the constant current driving chip before the dimming unit actually dims the LED, thereby protecting the chip from voltage damage while maintaining the brightness control function
Solution Approach 2:
The controllable switch unit acts as an intermediary between the power supply and the constant current driving chip. When the PWM signal is low, this intermediary switch opens the circuit, blocking the high voltage from reaching the chip. The switch synchronizes its operation with the dimming unit to ensure smooth brightness transition without exposing the chip to damaging voltages
Data Source
AI summary
A light emitting diode (LED) backlight driving circuit includes a power supply, an LED lightbar coupled to the power supply, and a constant current driving chip coupled to a control end of the power supply and coupled to a cathode of the LED lightbar. The constant current driving chip includes an adjusting dimming unit coupled to the cathode of the LED lightbar, and the adjusting dimming unit adjusts an external pulse-width modulation (PWM) dimming signal. A controllable switch unit is connected in series between an output end of the power supply and the constant current driving chip, and logical operation of the controllable switch unit is relative to logical operation of the adjusting dimming unit. The controllable switch unit turns off when the adjusting dimming unit turns off or before the adjusting dimming unit turns off, and the controllable switch unit turns on when the adjusting dimming unit turns on or after the adjusting dimming unit turns on.