GaN Boost Converter Soft Start With Synchronous Rectification
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Solution Overview
Problem
Existing boost converters face challenges such as high inrush currents during startup, power loss due to reverse recovery of silicon MOS switches and diodes, and limited operating frequency due to these losses, leading to inefficiencies and EMI issues.
Innovation Solution
A boost converter design utilizing a GaN-based solution with a pre-charging switch and a third GaN switch for synchronous output rectification, allowing for soft start-up, reduced power loss, and high-frequency operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large electrolytic capacitor is used to filter low frequency ripple, then the filtering performance is improved, but the inrush current during start-up increases significantly
Solution Approach 1:
The patent introduces a pre-charging switch and pre-charging resistor that are activated before the main circuit operation. The pre-charging resistor limits the inrush current during capacitor charging, and the pre-charging switch is turned off after the capacitor is charged to a predetermined voltage level. This preliminary action prevents the harmful inrush current while maintaining the necessary filtering performance of the large electrolytic capacitor.
2Device complexity
If silicon MOS switches and silicon diodes are used, then the device complexity is reduced, but power loss due to reverse recovery increases
Solution Approach 1:
The patent changes the material parameter of the switching devices from silicon to gallium nitride (GaN). GaN switches and diodes have fundamentally different electrical characteristics, particularly in reverse recovery behavior. The GaN body diode exhibits soft recovery characteristics with minimal reverse recovery current, thereby eliminating the reverse recovery power loss issue while maintaining device simplicity and reducing overall circuit complexity.
Solution Approach 2:
The patent employs a composite switching structure where both the main switch and the body diode are implemented using GaN technology. This composite approach combines the advantages of GaN material properties - high electron mobility, wide bandgap, and excellent reverse recovery characteristics - to simultaneously achieve low power loss and high efficiency in both switching and rectification functions.
3Ease of manufacture
If silicon switches and diodes are used, then the manufacturing cost is reduced, but the operating frequency is limited due to reverse recovery losses
Solution Approach 1:
The patent changes the material parameter from silicon to gallium nitride (GaN), which enables operation at much higher frequencies. The GaN body diode's soft recovery characteristic allows the circuit to operate at frequencies where silicon devices would suffer from excessive reverse recovery losses. This parameter change in material composition directly enables higher operating speeds while maintaining manufacturing feasibility through established GaN fabrication processes.
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
The design achieves a soft start-up to minimize inrush currents, reduces power loss by eliminating reverse recovery losses, and enables high-frequency operation, thereby improving efficiency and power density while reducing EMI.
Implementation Method 1
an output capacitor; a pre-charging switch connected between the node and the output capacitor, adapted to be conductive to charge the output capacitor from the node in a pre-charge phase
Implementation Method 2
the body diode of the third GaN switch can have small or nearly zero voltage drop in forward direction, and thus has very small power loss when the pre-charging switch conducts current from the input to the output capacitor. The third GaN switch can block the reverse current from the output capacitor to the input.
Implementation Method 3
A boost converter design utilizing a GaN-based solution with a pre-charging switch and a third GaN switch for synchronous output rectification, allowing for soft start-up, reduced power loss, and high-frequency operation
Data Source
AI summary
A boost converter has a main energy storage inductor and a main GaN boost switch with a node between them. A pre-charging switch is connected at the output side of the main boost switch and the inductor, between the node and an output capacitor. The pre-charging switch comprises a body diode in the forward direction from the output capacitor to the node. The output capacitor is charged by the pre-charging switch in a pre-charge phase and this provides a soft start-up to avoid large inrush currents. A third switch, which is also a GaN switch, is in series with the pre-charging switch to provide synchronous output rectification. The third switch has a body diode in a forward direction from the node to the output capacitor. In the pre-charge phase, both the boost switch and third switch are turned off whereas in a subsequent boost phase, the pre-charging switch is turned constantly on, and alternately the boost switch and the third switch are turned on and off to implement the boost conversion.