Floating Buck-Boost Regulator for Low Ripple LED Drivers
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Solution Overview
Problem
Existing DC/DC switch mode power supply converters for driving LED strings require additional switches, leading to increased cost, size, and electromagnetic interference (EMI) due to the transition between buck and boost modes, and fail to smoothly regulate both input and output ripples.
Innovation Solution
A novel configuration using an off-the-shelf buck controller IC with two switching transistors or a diode, coupled with two inductors for input and output ripple smoothing, allowing for efficient voltage regulation across a floating LED string with minimal EMI by controlling peak current through the high side MOSFET and smoothing switching noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a buck-boost converter with four switches is used to achieve voltage regulation for floating LED strings, then the voltage can be boosted or bucked as needed, but the additional switches increase cost, size, and EMI
Solution Approach 1:
The patent divides the conversion process into two separate stages: a boost stage followed by a buck stage. Each stage uses its own inductor and switching transistor, allowing independent optimization of each conversion phase. This segmentation enables the use of simpler, fewer components overall compared to a single four-switch buck-boost converter, while maintaining the ability to handle both boosting and bucking scenarios.
Solution Approach 2:
The patent employs dynamic control of the switching transistors to adapt the converter operation between boost and buck modes. By dynamically adjusting the duty cycles of the boost and buck stages, the system can accommodate varying LED string requirements without needing additional hardware switches, reducing device complexity while maintaining versatility.
2Device complexity
If a conventional boost or buck converter is used, then the circuit is simple with fewer components, but it cannot simultaneously achieve low input voltage ripple and low output voltage ripple
Solution Approach 1:
The patent segments the ripple filtering function into two separate inductors: one dedicated to input ripple smoothing and another dedicated to output ripple smoothing. This segmentation allows each inductor to be optimized for its specific filtering task, achieving low EMI at both input and output while maintaining a relatively simple circuit architecture.
Solution Approach 2:
The patent introduces an intermediate capacitor between the boost and buck stages that serves as a mediator for voltage stabilization. This intermediate element helps decouple the input and output ripple characteristics, allowing each stage to operate independently with minimal interference, thereby achieving low EMI without significantly increasing circuit complexity.
3Adaptability or versatility
If four switches are used in a buck-boost converter to achieve voltage conversion, then both buck and boost functions are available, but the transition between modes creates noise and increases EMI
Solution Approach 1:
The patent segments the voltage conversion function into distinct boost and buck stages, each with its own switching transistor. This segmentation eliminates the need for mode transitions between buck and boost operations, as each stage operates continuously in its designated mode. The boost stage handles voltage elevation while the buck stage handles voltage reduction, preventing the noise and EMI associated with mode switching in conventional buck-boost converters.
Solution Approach 2:
The patent performs preliminary voltage boosting before the buck conversion stage. By pre-adjusting the voltage to an appropriate level in the boost stage, the subsequent buck stage operates under optimized conditions, avoiding the need for dynamic mode transitions that generate noise. This preliminary action stabilizes the operating conditions and reduces harmful emissions.
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 configuration reduces EMI and cost by using only two switches or one diode, effectively regulating current through the LED string with low input and output ripples, achieving efficient and cost-effective LED lighting.
Implementation Method 1
where a first inductor smoothes input current or input voltage ripple
Implementation Method 2
where a second inductor smoothes output current or output voltage ripple
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
A converter generates an output voltage differential across a floating load, such as a string of LEDs. The converter receives an input voltage Vin from a power supply, and the floating output voltage differential may be greater than or less than Vin. The converter uses a first switch and first inductor in a boost mode type configuration, and uses a second switch and second inductor in a buck mode type configuration. The inductors have a common node. The first inductor has another end coupled to ground, and the other end of the second inductor is coupled to the load. Both inductors charge and discharge together depending on the conductivities of the switches. One end of the load will be approximately zero volts, while the other end will be at a negative voltage VEE. The two inductors smooth input current/voltage ripple and output current/voltage ripple, resulting in low EMI.