Cascode GaN Transistor Drive Circuit for Stable Gate-Source Bias
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Solution Overview
Problem
Conventional drive circuits for normally-ON transistors, particularly those using gallium nitride (GaN) materials, face challenges in maintaining reliable ON and OFF switching characteristics due to fluctuations in threshold voltage, leading to deterioration in performance when the gate-source voltage becomes positive.
Innovation Solution
A drive circuit and method that incorporates a cascode connection between a normally-ON GaN transistor and a normally-OFF silicon (Si) transistor, utilizing a buffer circuit with adjustable bias voltages to control the gate-source voltage of the normally-ON transistor, preventing positive voltage states and ensuring reliable switching without characteristic deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the gate-source voltage is raised to reduce ON resistance, then driving capacity is improved, but threshold voltage fluctuates causing characteristic deterioration
Solution Approach 1:
A buffer circuit is introduced as an intermediary between the control signal source and the normally-ON transistor gate. This buffer circuit includes a normally-OFF transistor that mediates the voltage transmission, ensuring the gate-source voltage remains within the safe range (≤0V) while still enabling effective control of the normally-ON transistor for high driving capacity.
Solution Approach 2:
The invention changes the operational parameters by using a normally-OFF transistor in the buffer circuit instead of a conventional voltage divider or direct connection. This allows dynamic control of the gate voltage based on the normally-OFF transistor's switching state, adapting the voltage parameters to prevent threshold fluctuation while maintaining driving capacity.
2Device complexity
If a conventional drive circuit is used, then the structure is simple, but positive gate-source voltage causes threshold fluctuation and characteristic deterioration
Solution Approach 1:
The buffer circuit with normally-OFF transistor serves as an intermediary that adds minimal complexity while providing critical protection against positive gate-source voltage. The normally-OFF transistor acts as a voltage gatekeeper, blocking positive voltages from reaching the normally-ON transistor gate, thus protecting against threshold fluctuation.
Solution Approach 2:
The drive circuit employs a composite structure combining normally-ON GaN transistor and normally-OFF transistor in a cascode configuration. This composite approach leverages the high-frequency characteristics of GaN while using the normally-OFF transistor's voltage blocking capability to protect against threshold fluctuation, achieving both performance and reliability.
3Reliability
If the gate-source voltage is controlled to prevent positive values, then characteristic stability is maintained, but driving capacity may be reduced
Solution Approach 1:
The buffer circuit dynamically adjusts the gate voltage based on the switching state of the normally-OFF transistor. During normal operation, the normally-OFF transistor conducts and allows appropriate negative gate voltages to achieve low ON resistance and high driving capacity. During protection mode, it blocks positive voltages, thus dynamically adapting to maintain both stability and performance.
Solution Approach 2:
The invention changes the voltage parameter control strategy by using the normally-OFF transistor's on/off states to modulate the gate voltage. When the normally-OFF transistor is ON, the gate can achieve sufficient negative voltage for low resistance. When it turns OFF, positive voltage is blocked, preventing threshold fluctuation. This parameter modulation maintains both stability and driving capacity.
Data Source
AI summary
According to one aspect of embodiments, a drive circuit of a normally-ON transistor includes: a normally-OFF transistor that includes a main current path connected in serial to a main current path of the normally-ON transistor; and a buffer circuit that supplies, to a gate of the normally-ON transistor, a control signal for controlling turning ON and OFF of the normally-ON transistor, whose high-voltage side and low-voltage side are biased by a bias voltage supplied from a power source unit.