GaN Power Switch Voltage Clamp for Unclamped Inductive Switching
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Solution Overview
Problem
Lateral Gallium nitride (GaN) power devices lack avalanche handling capability, leading to device destruction during unclamped inductive switching events, limiting their use in applications requiring both unclamped and static switch conditions.
Innovation Solution
Incorporating a voltage clamp circuit in parallel with the main power switch, featuring a pulldown switch, series-connected diodes, and a voltage clamp device, which absorbs energy before breakdown, providing a clamp voltage less than the breakdown voltage of the main power switch to prevent avalanche breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If lateral GaN power devices are used for their high breakdown voltage and low on-state resistance, then power efficiency is improved, but avalanche handling capability is lost leading to device destruction during unclamped inductive switching
Solution Approach 1:
The patent introduces a voltage clamp circuit as an intermediary protective mechanism between the inductive load and the GaN power device. This circuit includes a clamp switch, clamp diode, and energy storage capacitor that activate during unclamped inductive switching events to limit voltage across the main power device, preventing avalanche breakdown while allowing the GaN device to maintain its inherent high efficiency characteristics
Solution Approach 2:
The voltage clamp circuit provides beforehand cushioning by pre-positioning energy absorption capabilities through the clamp capacitor and diode. When unclamped inductive switching occurs, this pre-configured protection mechanism immediately activates to absorb the voltage spike, cushioning the GaN power device from destructive avalanche conditions before damage can occur
2Reliability
If a voltage clamp circuit is added to provide avalanche protection, then reliability is improved, but device complexity increases
Solution Approach 1:
The voltage clamp function is extracted as a separate, dedicated circuit module rather than attempting to integrate avalanche protection directly into the GaN power device structure. This extraction allows the main power device to remain simple while the protective function is handled by the external clamp circuit, which can be designed as a modular add-on
Solution Approach 2:
The voltage clamp circuit uses relatively simple, low-cost components (diodes, capacitors, and a clamp switch) that can be easily replaced if needed, providing robust protection without significantly increasing system complexity or cost. The clamp diode and capacitor are passive components with no active control requirements
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 voltage clamp circuit effectively absorbs inductive energy during unclamped inductive switching, preventing destructive avalanche breakdown and enhancing the operational reliability of GaN power devices, while also being adaptable for use in other semiconductor technologies like Si and SiC.
Implementation Method 1
Avalanche breakdown occurs in semiconductor devices when the electric field is strong enough such that mobile electrons or holes are accelerated to high enough speeds to knock other bound carriers free, creating more free charge carriers and thereby increasing the current and creating an avalanche during which large portions of a normally insulating crystal begin to conduct.
Data Source
AI summary
A power semiconductor device includes: a main power switch having a drain, source, and gate; and a voltage clamp circuit in parallel with the main power switch and having a clamp voltage less than a breakdown voltage of the main power switch. The voltage clamp circuit includes: a pulldown switch having a normally-on gate electrically connected to the source of the main power switch; a plurality of series-connected diodes electrically connected between the drain of the main power switch and a drain of the pulldown switch; a voltage clamp device electrically connected between a source of the pulldown switch and the source of the main power switch; and a second power switch having a normally-off gate electrically connected to the drain of the pulldown switch, a drain electrically connected to the drain of the main power switch, and a source electrically connected to the source of the pulldown switch.