GaN Startup Circuit for Low-Standby SMPS Power-Up
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Solution Overview
Problem
Existing switched-mode power supply (SMPS) systems face challenges in providing initial startup power to control and switching circuits before the SMPS is fully operational, as they rely on the SMPS itself to generate the necessary DC power supply voltage.
Innovation Solution
A GaN-based startup circuit is used to provide the initial DC power supply voltage to the control and switching circuits by utilizing a normally-on GaN transistor integrated on the same semiconductor substrate as a normally-off GaN transistor, allowing for efficient startup with minimal standby current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a traditional silicon-based transistor is used in SMPS, then the device can operate, but switching losses are high
Solution Approach 1:
The patent changes the material parameter from silicon to gallium nitride (GaN), which fundamentally alters the electrical characteristics including lower parasitic capacitance and lower on-resistance. This material substitution directly reduces switching losses and improves power conversion efficiency while maintaining the transistor's switching function.
2Loss of energy
If a normally-on GaN transistor is used for startup, then startup efficiency is improved with minimal standby current, but the transistor remains conductive when gate voltage is removed
Solution Approach 1:
The normally-on GaN transistor is used specifically for the preliminary startup phase before the main control circuit becomes operational. During this initial phase, the transistor provides power to the control circuit without requiring active control. Once the control circuit is powered, it takes over and can properly control the main switching transistor, thus the preliminary action of the normally-on transistor does not compromise overall system reliability.
3Productivity
If GaN power devices are used to reduce switching losses, then power conversion efficiency is improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent merges the startup transistor and main switching transistor onto the same GaN semiconductor substrate, integrating multiple functions into a single device structure. This integration reduces the overall system complexity compared to using separate silicon devices, simplifies the bill of materials, and leverages the manufacturing advantages of GaN technology to offset the inherent complexity of wide-bandgap material processing.
Data Source
Figure 1A~1D
Figure 2~3
Figure 4A
AI summary
In accordance with an embodiment, a circuit includes a first gallium nitride (GaN) transistor comprising a drain coupled to a drain node, a source coupled to a source node, and a gate coupled to a gate node; and a second GaN transistor comprising a drain coupled to the drain node, a source coupled to a first power source node configured to be coupled to a first capacitor.