Multi-Level Half-Bridge Power Conversion for LED Drivers
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Solution Overview
Problem
High voltage switches in state-of-the-art offline AC/DC converters face limitations due to high drain-source and gate-source capacitances, restricted switching frequency, and limited availability of low-cost high voltage switches for Very Large Scale Integration (VLSI), hindering efficient power conversion and integration in compact LED drivers.
Innovation Solution
A power conversion system with a segmented PFC boost converter stage and a multi-level half-bridge stage, using a selection module and controller to manage switching nodes and voltage levels, reducing voltage stress on switches and capacitors, and employing a switched capacitor converter with a Dickson ladder topology for efficient power combining.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high voltage switches are used in state-of-the-art offline AC/DC converters, then the blocking voltage capability is improved, but the drain-source and gate-source capacitances increase, limiting the switching frequency
Solution Approach 1:
The patent divides the high voltage blocking task into multiple segments by using a multi-level half-bridge topology where several switches work in series. Each switch only needs to block a fraction of the total voltage (e.g., 400V/4 = 100V per switch), allowing the use of low-voltage switches that operate at higher frequencies with lower capacitances.
Solution Approach 2:
The patent introduces intermediate voltage levels through the multi-level half-bridge structure, which acts as a mediator between the high voltage input and the low voltage output. This intermediary structure enables the use of low-voltage switches while still handling high voltage applications.
2Strength
If high voltage switches are used, then the blocking voltage capability is improved, but the switching losses increase proportionally to the square of the blocking voltage
Solution Approach 1:
By segmenting the voltage blocking across multiple switches in series, each switch experiences lower voltage stress. Since switching losses are proportional to the square of the blocking voltage, reducing the voltage per switch from 400V to 100V reduces switching losses by a factor of 16 (400²/100²), significantly improving efficiency.
3Ease of operation
If conventional Inductive Converters are used, then fine regulation of output power is achieved, but integration in compact structures becomes difficult
Solution Approach 1:
The patent replaces the mechanical/magnetic inductor-based power conversion system with an electronic switched-capacitor system. The multi-level half-bridge circuit uses capacitors and switches instead of large inductors, enabling fine power regulation through electronic switching while achieving compact integration suitable for LED driver applications.
4Device complexity
If Switched Capacitor Converters are used, then high level of integration and large power conversion ratios are achieved, but only plural discrete conversion ratios are provided, preventing fine regulation
Solution Approach 1:
The patent introduces dynamic control capability to the switched-capacitor converter through the multi-level half-bridge topology. By dynamically switching between different capacitor combinations and voltage levels in real-time, the system can continuously adjust the output power, transforming the static discrete conversion ratios into a dynamic fine-regulation system.
Data Source
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Figure 3a~3b
AI summary
A system for supplying a load comprising: an input inductor configured to receive an input voltage, a selection module connected to the inductor via a switching node, and a multi-level half-bridge stage comprising a plurality of half-bridge stages, each half-bridge stage comprising a pair of switches connected between a switching node; a power combining stage coupled to each half-bridge stage using parallel bus voltage lines output from the multi-level half-bridge stage, the power combining stage configured to output a voltage to the load; and a controller configured, based on the input voltage, to selectively control a half-bridge stage to operate in a half-bridge mode to provide a stepped-up voltage on a bus voltage line, wherein the controller is further configured to control the power combining stage to provide a voltage between the bus voltage lines and the sum of these voltages is higher than a peak of the input voltage.