Time-Multiplexed LED Backlight Power Supply Circuit
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Solution Overview
Problem
Existing power supply circuits for LED backlighting suffer from significant power losses due to voltage differences across individual LED strings, leading to increased complexity, space requirements, and costs when using dedicated voltage converters for each string.
Innovation Solution
A controlled power supply circuit that activates multiple load strings in a time-multiplexed fashion, using a clocked current source with charge storage and sensors to distribute energy efficiently, allowing for different voltage drops across load strings while minimizing power losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single DC/DC converter supplies power to multiple LED strings in parallel, then device complexity is reduced, but power losses increase due to voltage differences across individual strings
Solution Approach 1:
The patent applies periodic action by sequentially switching between different LED strings using a multiplexer controlled by a ring counter. Each LED string is activated in turn during specific time intervals (e.g., String 1 during interval T1, String 2 during interval T2), allowing the single DC/DC converter to supply current pulses to each string individually. This time-division multiplexing eliminates the voltage mismatch problem that occurs when multiple strings are powered simultaneously, thereby reducing power losses while maintaining a single converter architecture.
Solution Approach 2:
The patent segments the power delivery process by dividing it into distinct time intervals for each LED string. The ring counter generates sequential control signals that isolate each LED string's power supply in time, effectively segmenting the overall power distribution into separate, non-overlapping phases. This segmentation allows the converter to optimize current delivery to each string individually, avoiding the energy losses caused by parallel connection voltage differences.
2Loss of energy
If dedicated voltage converters are provided for each LED string, then power losses are reduced, but device complexity and manufacturing costs increase
Solution Approach 1:
The patent merges the functionality of multiple dedicated converters into a single DC/DC converter by introducing a time-multiplexing control mechanism. The ring counter and multiplexer combine the control functions that would otherwise require separate converters, allowing one converter to perform the roles of multiple converters through sequential operation. This merging approach achieves the power efficiency of dedicated converters while eliminating their individual hardware requirements.
Solution Approach 2:
The single DC/DC converter is designed with universal functionality to serve multiple LED strings through time-division multiplexing. The converter's output is routed to different strings sequentially via the multiplexer, making the single converter capable of performing the power supply function that would traditionally require multiple specialized converters. This multi-functionality is controlled by the ring counter which coordinates the switching between different string connections.
3Illumination intensity
If multiple LED strings are activated simultaneously, then illumination coverage is improved, but power losses increase due to voltage differences
Solution Approach 1:
The patent uses periodic action through fast sequential switching to achieve both illumination coverage and energy efficiency. The ring counter generates time-multiplexed control signals that activate different LED strings in rapid succession (e.g., String 1 during T1, String 2 during T2, String 3 during T3). This periodic switching creates the perception of continuous illumination while actually delivering power to each string individually during its designated time interval, thereby maintaining coverage without the power losses of simultaneous parallel activation.
Solution Approach 2:
The patent maintains continuous useful action by ensuring that the sequential activation of LED strings creates uninterrupted backlighting. The ring counter coordinates the switching timing so that as one string is deactivated, another is activated, maintaining continuous illumination coverage. This continuous action approach allows the system to achieve full-area backlighting without the energy waste of simultaneous activation, as each string receives optimized current during its active interval.
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 enables efficient power distribution to load strings with varying voltage drops, reducing power losses and manufacturing costs by using a single current source and charge storage, while ensuring sufficient voltage and current supply to each string.
Implementation Method 1
The current source comprises an energy storage means such as, for example, a coil that delivers a current to the load strings during the operation. The clocked current source may be designed for filling the energy storage means during a first time period and for delivering the energy stored therein to the load strings arranged in parallel during a second time period.
Data Source
AI summary
A power supply circuit for supplying power to at least two loads which are connected to said power supply circuit comprises a current source which can be operated in a clocked manner and has a control input for adjusting the power. At least two load strings are connected in parallel between a power supply connection, which is coupled to the current source, and a reference connection. Each load string has a load and charge storage means which is connected in parallel with the load. A switch is used to selectively switch the current path of the load string. A sensor having a sensor resistor which is connected in the current path of the load string is used to detect a current flowing through the connected load string. Furthermore, the controlled power supply circuit comprises a control circuit which is coupled to the switch and to the sensor of each load string for the purpose of activating each load string in a time-multiplexed manner.