LED Backlight Device Using Series Transformers for Constant Current
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Solution Overview
Problem
Conventional LED backlight devices for liquid crystal display devices face issues with power loss and heat generation due to varying forward voltages across LED strings, which complicates the control system and requires feedback circuits for current or terminal voltage detection, making it difficult to adjust circuit parameters and minimize heat.
Innovation Solution
The proposed LED backlight device employs an inverter that outputs AC current, with transformers and full-wave rectification circuits configured to provide constant current to LED strings, eliminating the need for current driving circuits and bottom detecting circuits, and includes a DC converter to compensate for voltage differences between LED strings, simplifying the circuit structure and reducing heat loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current driving circuits with feedback loops are used to control LED strings, then current control precision is improved, but device complexity and heat generation increase
Solution Approach 1:
The patent extracts and removes the feedback control components (error amplifiers, bottom detecting circuits) from the LED driving system. Instead of using complex feedback loops to detect and adjust current, the invention uses a simple series connection of transformers where the primary winding current directly controls the secondary output current through magnetic coupling, eliminating the need for active feedback control while maintaining precise current control.
Solution Approach 2:
The patent replaces the electronic feedback control system with a magnetic field-based control mechanism. The current control is achieved through electromagnetic induction in transformers, where the magnetic coupling between primary and secondary windings provides inherent current control without requiring electronic feedback loops, sensors, or active adjustment circuits.
2Adaptability or versatility
If DC converters with bottom detecting circuits are used to adjust voltages for LED strings, then voltage matching is improved, but power loss and heat generation increase
Solution Approach 1:
The patent removes the DC converter and bottom detecting circuit from the system. Instead of actively converting and adjusting DC voltages to match LED string requirements, the invention allows each LED string to operate with its natural forward voltage characteristics while maintaining uniform current through the transformer series connection, eliminating the energy-lossy voltage conversion process.
Solution Approach 2:
Each LED string naturally operates at its own forward voltage without requiring external voltage adjustment. The system self-regulates by allowing different voltage drops across different LED strings while the series-connected transformers ensure uniform current distribution, eliminating the need for active voltage matching circuits.
3Measurement precision
If multiple current driving circuits are used for each LED string, then current control accuracy is improved, but ease of manufacture and circuit simplicity deteriorate
Solution Approach 1:
The patent merges multiple independent current driving circuits into a single unified system. By connecting transformer primary windings in series, the system uses one common current path to control all LED strings simultaneously, eliminating the need for multiple separate driving circuits and their associated feedback loops, thereby simplifying assembly while maintaining control accuracy.
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
This solution simplifies the circuit structure, reduces heat loss, and maintains constant current flow across LED strings, eliminating the need for complex feedback circuits and allowing for easier grounding, thereby minimizing power consumption and heat generation.
Implementation Method 1
an inverter having an input connected to a DC power supply and configured to output an AC current
Implementation Method 2
a plurality of transformers each configured to drop the AC current input from the inverter
Implementation Method 3
a plurality of full-wave rectification circuits respectively connected to the output sides of the transformers, and configured to full-wave rectify the dropped AC currents
Implementation Method 4
a plurality of smoothing circuits respectively connected to outputs of the plurality of full-wave rectification circuits, and configured to smooth the full-wave rectified currents to output DC currents
Data Source
AI summary
An LED backlight device includes an inverter having an input connected to a DC power supply to provide an output AC current. A plurality of transformers are each configured to drop AC current input from the inverter. Input sides of the transformers are connected in series to an output of the inverter and output sides of the transformers are disposed in parallel. A plurality of full-wave rectification circuits are respectively connected to the output sides of the transformers and full-wave rectify the dropped AC currents, respectively. A plurality of smoothing circuits are respectively connected to outputs of the full-wave rectification circuits, and are configured to smooth the full-wave rectified currents to output DC currents, respectively. A plurality of LED strings are respectively connected to the outputs of the smoothing circuits and each of the LED strings have a plurality of LEDs.