LED Driver Circuit with Voltage-Dependent Switching
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Solution Overview
Problem
Existing LED driver circuits face inefficiencies due to variability in forward voltage of LEDs, leading to significant losses and increased costs when driving multiple LED strings, as they require individual current control and often result in high RMS currents and complex transformer designs.
Innovation Solution
A switch mode converter with a resonant transformer and a switching control circuit that operates output circuit switches in an order dependent on the forward voltage of each LED, maintaining a set current through each load without a voltage drop, and using pulse width modulation for power control without changing the driving current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a two stage approach with a current source is used to control multiple LED strings, then current control is achieved, but significant voltage drops occur leading to energy losses
Solution Approach 1:
The patent applies dynamics by making the switching control circuit operate output circuit switches in an order dependent on forward voltage of each LED string. The switching sequence is dynamically adjusted based on measured forward voltages, allowing the system to adapt to varying LED characteristics and eliminate the need for a dissipative current source while maintaining proper current control.
Solution Approach 2:
The patent changes the operating parameters by switching output circuit switches in a specific sequence based on forward voltage measurements. By controlling the switching timing and sequence rather than using a fixed voltage drop approach, the system achieves current control without the energy losses associated with traditional current sources.
2Loss of energy
If individual switched mode power stages are used for each LED string, then losses are reduced, but circuit board area and cost increase considerably
Solution Approach 1:
The patent merges multiple LED string control functions into a single switch mode converter with a unified control circuit. Instead of having separate power stages for each LED string, the invention combines them into one converter that drives multiple strings through shared components (transformer, control circuit), thereby reducing circuit board area and component count while maintaining efficiency.
Solution Approach 2:
The switch mode converter is designed with multi-functionality to drive multiple LED strings simultaneously. The single converter unit can control multiple output circuits, each connected to different LED strings, making the system more compact and cost-effective compared to individual dedicated power stages for each string.
3Device complexity
If parallel connection is used to drive multiple LED strings, then circuit complexity is reduced, but forward driving voltage varies causing unequal power distribution
Solution Approach 1:
The patent implements feedback by measuring the forward voltage of each LED string and using this information to control the switching sequence of output circuit switches. The switching control circuit adjusts its operation based on the measured forward voltages, ensuring that each LED string receives the appropriate power despite variations in forward voltage characteristics.
Solution Approach 2:
The patent applies preliminary action by measuring the forward voltage of each LED string before switching and using this pre-acquired information to determine the optimal switching sequence. This preliminary measurement allows the control circuit to anticipate and compensate for voltage variations, ensuring equal power distribution across all LED strings.
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 approach reduces RMS currents and eliminates voltage drops, enhancing efficiency and allowing for independent control of multiple LED strings with reduced complexity and cost, while maintaining stable current delivery across varying LED voltages.
Implementation Method 1
a switch mode converter being a resonant converter and comprising a transformer with primary and secondary windings
Implementation Method 2
a switch mode converter being a resonant converter
Data Source
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AI summary
The disclosure relates to circuits for driving a plurality of electrical loads and to methods for operating such circuits, where each electrical load is driven according to a desired current. Exemplary embodiments include a circuit (100) comprising a switch mode converter (101) comprising a transformer (102) with primary and secondary windings, the primary winding (103) connected to a voltage supply (104) via one or more input control switches (105a, 105b); a plurality of output circuits (106a-c), each output circuit comprising a switch (107a-c) connecting one of the plurality of electrical loads (108a-c) to an output (109a-c) of the secondary winding (110), each electrical load (108a-c) connected in series with a respective switch (107a-c) and in parallel with a capacitor (112a-c); and a switching control circuit (113) connected for control of each of the output circuit switches (107a-c) and for sensing of a current through each of the electrical loads (108a-c), wherein the switching control circuit (113) is configured to operate the output circuit switches (107a-c) to maintain a set current through each of the electrical loads (108a-c), the switching control circuit (113) configured in successive output cycles of the switch mode converter (101) to operate each of the output circuit switches (107a-c) in an order dependent on a forward voltage of each of the respective electrical loads (108a-c).