Class D Amplifier Bi-Directional GaN Switches
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Solution Overview
Problem
Traditional half-bridge circuits require additional diodes for bi-directional current flow, which can lead to short circuits and increased component damage when the DC bus voltage goes negative, and they are inefficient due to the need for separate PFC converters to achieve high power factor and low THD.
Innovation Solution
A Class D amplifier circuit utilizing bi-directional HEMT/GaN switches eliminates the need for diodes by using high electron mobility transistors (HEMTs) in a totem pole configuration, allowing direct connection to an AC line voltage and enabling bi-directional current flow without diodes, and incorporating a zero-voltage crossing circuit for precise switch control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional MOSFETs with body diodes are used in half-bridge circuit, then current can flow in one direction, but additional diodes are required for bi-directional current flow which increases component count and risk of short circuits
Solution Approach 1:
The patent removes the body diodes from the MOSFET structure and replaces them with independent bi-directional switches (S1, S2) in the half-bridge circuit. This extraction of the diode function allows for bi-directional current flow while reducing the risk of short circuits that occur with traditional diode configurations when DC bus voltage goes negative.
Solution Approach 2:
The patent changes the switching parameters by introducing zero-voltage crossing detection and control. The bi-directional switches are controlled to turn on only when the voltage across them is zero, which prevents shoot-through currents and enables safe bi-directional operation. This parameter change in switching timing enables versatility without increasing complexity.
2Reliability
If separate PFC converter is used to achieve high power factor and low THD, then power quality is improved, but device complexity and component count increase
Solution Approach 1:
The patent merges the PFC (Power Factor Correction) function with the main power conversion stage by using bi-directional switches that can operate in both rectification and inversion modes. This single-stage configuration achieves high power factor and low THD without requiring a separate PFC converter, thereby improving reliability while reducing device complexity.
Solution Approach 2:
The bi-directional switches (S1, S2) are designed to perform multiple functions: they act as rectifier switches during the rectification phase and as inverter switches during the power delivery phase. This multi-functionality eliminates the need for separate PFC and inverter stages, achieving high power quality with a single integrated circuit stage.
3Stability of the object's composition
If diodes are used for current path during dead time, then continuous current is maintained, but component count and potential failure points increase
Solution Approach 1:
The bi-directional switches (S1, S2) are designed to automatically provide the current path during dead time without requiring external diodes. The switches can conduct current in both directions and can maintain continuous current flow through the load during the dead time period, making the system self-sufficient and eliminating additional components.
Data Source
AI summary
A Class D amplifier circuit in accordance with an embodiment of the present application includes a converter stage operable to provide a desired AC voltage and a Class D amplifier stage, connected to the converter stage. The Class D amplifier stage includes a first bi-directional switch connected to the converter stage, a second bi-directional switch, connected in series with the first bi-directional switch, wherein the first and second bi-directional switches are connected across the desired AC voltage provided by the converter stage and a controller operable to turn the first and second bi-directional switches ON and OFF such that a desired voltage is provided at a midpoint node positioned between the first bi-directional switch and the second bi-directional switch.