Transistor Driver Circuit With Floating Power Supply Bias
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Solution Overview
Problem
Existing systems for driving switching transistors, particularly normally-on devices like GaN HEMT and JFET, face challenges in reliably turning off these transistors due to their negative threshold voltage, which can lead to conductive states at zero bias conditions, requiring additional voltage generation and complex driver circuits to manage threshold variations over temperature and operational changes.
Innovation Solution
A circuit with a floating power supply and a common-mode bias circuit that provides time-dependent voltages, using a replica transistor to approximate the threshold voltage of the switching transistor, allowing for efficient turning on and off by alternating between positive and negative voltages, and incorporating a floating power supply with a center-tapped transformer for improved voltage regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a negative voltage is generated to turn off normally-on transistors, then the transistor can be turned off reliably, but the driver circuit complexity increases
Solution Approach 1:
A common-mode control terminal is introduced as an intermediary between the power supply and the gate drive circuit. This terminal receives a common-mode voltage that adjusts the threshold voltage of the transistor, enabling reliable turn-off without requiring complex negative voltage generation circuits in the driver itself
Solution Approach 2:
The threshold voltage of the transistor is dynamically changed by applying a time-dependent voltage to the common-mode control terminal. This parameter change allows the transistor to be turned off reliably while simplifying the driver circuit, as the threshold adjustment is achieved through external voltage control rather than internal circuit complexity
2Reliability
If provisions are made to ensure normally-on devices can be turned off, then switching reliability improves, but additional voltage generation is required
Solution Approach 1:
The common-mode control terminal serves multiple functions: it adjusts the threshold voltage, enables reliable turn-off, and simplifies the overall voltage generation requirements. By making this single terminal multi-functional, the patent avoids the need for separate negative voltage generation circuits while maintaining switching reliability
3Reliability
If threshold voltage variations over temperature are managed, then switching performance is maintained, but driver circuit complexity increases
Solution Approach 1:
The common-mode control terminal provides a feedback mechanism where the threshold voltage is continuously adjusted based on temperature-dependent voltage applications. This feedback loop maintains consistent switching performance across temperature variations without requiring complex temperature sensing and compensation circuits within the driver
Data Source
AI summary
In accordance with an embodiment, a circuit for driving a control terminal of a switching transistor includes a driver having an output configured to be coupled to the control terminal of the switching transistor, a first power supply terminal configured to be coupled to a first terminal of a floating power supply, a second power supply terminal configured to be coupled to a second terminal of the floating power supply, and a switching input terminal configured to receive a switching signal. The circuit further includes a bias circuit having an output terminal configured to be coupled to a common-mode control terminal of the floating power supply, wherein the bias circuit is configured to provide a time dependent voltage.