LED Backlight Driver Circuit with Continuous Current Detection
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Solution Overview
Problem
Conventional LED driving circuits for LCD panel backlights struggle with precise detection of driving current, leading to irregular current flow and difficulty in maintaining a constant current value due to detection blanks and unstable PWM control.
Innovation Solution
An improved LED driving circuit design that includes a switch, rectifying diode, smoothing capacitor, and PWM controlling part with a comparator and controller, which determines the duty ratio of switching pulses based on detected voltage to ensure continuous and stable current detection and control, eliminating detection blanks and maintaining constant current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional PWM boost type DC-DC converter is used for LED driving, then the circuit can provide basic voltage conversion and LED illumination, but the driving current detection is imprecise and detection blanks occur leading to unstable current control
Solution Approach 1:
The patent introduces a dedicated current detection circuit as an intermediary component between the LED array and the control system. This separate detection path, using a detection resistor and operational amplifier, provides accurate current measurement without interfering with the main power conversion function, thereby resolving the contradiction between basic voltage conversion and precise current detection
Solution Approach 2:
The patent implements a closed-loop feedback mechanism where the detected current signal is continuously fed back to the PWM controller. The controller adjusts the switching duty cycle based on the feedback signal to maintain constant current, eliminating detection blanks and ensuring stable current control while maintaining the basic voltage conversion function
2Ease of operation
If the switching pulse duty ratio is adjusted based on detection voltage magnitude, then PWM control can regulate current flow, but detection blanks and irregular current flow occur preventing constant current maintenance
Solution Approach 1:
The patent ensures continuous current detection by maintaining the detection circuit operation throughout the entire switching cycle. The detection resistor and operational amplifier continuously monitor the current flow, eliminating detection blanks and ensuring the PWM controller receives uninterrupted feedback for consistent current regulation
Solution Approach 2:
The patent employs dynamic PWM control where the duty ratio is continuously adjusted based on real-time detection voltage feedback. The control system dynamically responds to current variations, maintaining ease of operation through adjustable duty cycle while ensuring current flow consistency through continuous feedback regulation
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
The improved circuit achieves precise and continuous detection of driving current, enabling stable PWM control and maintaining constant current flow through the LED array, reducing offset between color channels and ensuring consistent brightness and color reproducibility.
Implementation Method 1
a voltage detecting resistor Rd connected between the other terminal of the smoothing capacitor and to the other end of the LED array connected to the ground to detect voltage from the current flowing to the ground
Implementation Method 2
a rectifying diode connected between a connecting node and one terminal of the LED array to rectify driving voltage supplied according to switching operation of the switch
Implementation Method 3
a smoothing capacitor having one terminal connected to a cathode of the rectifying diode and the other terminal connected to a ground
Data Source
AI summary
An LED driving circuit of a backlight unit includes a switch connected between an input of direct voltage and a ground to switch the direct voltage according to a switching pulse; a rectifying diode connected between a connecting node and one terminal of the LED array to rectify driving voltage supplied according to switching operation of the switch; a smoothing capacitor having one terminal connected to a cathode of the rectifying diode and the other terminal connected to a ground; a voltage detecting resistor connected between the other terminal of the LED array connected to the ground and the other end of the smoothing capacitor to detect voltage from the current flowing to the ground; and a PWM controlling part for controlling on/off status of the switching according to the switching pulse, wherein the switching pulse has a duty ratio determined according to a preset internal reference voltage and the voltage detected by the voltage detecting resistor. The driving current of can be controlled at a constant current and thus be stabilized.