Cascode Power Transistor Circuit for High Breakdown Voltage
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Solution Overview
Problem
The on-resistance of unipolar semiconductor power devices scales proportionally to the square of the rated voltage, leading to inefficiencies and potential device malfunction at high breakdown voltages.
Innovation Solution
A cascode configuration is employed, combining a first power transistor and a second power transistor with a voltage divider circuit that indirectly couples the gate terminal of the first transistor to the source terminal of the second transistor, using diodes and capacitors to limit the gate-source voltage of the first transistor below its maximum rating, allowing for higher breakdown voltages and reduced on-resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the breakdown voltage of a unipolar semiconductor power device is increased, then the device can withstand higher voltages, but the on-resistance increases proportionally to the square of the rated voltage
Solution Approach 1:
The patent divides the single high-voltage transistor into two separate transistors connected in cascode configuration. The first transistor handles the high voltage stress while the second transistor provides low on-resistance current conduction. This segmentation allows each transistor to be optimized for its specific function, resolving the contradiction between high breakdown voltage and low on-resistance that plagues single-transistor designs.
Solution Approach 2:
The voltage divider circuit acts as an intermediary between the gate of the first transistor and the source of the second transistor. It indirectly couples these terminals while limiting the gate-source voltage of the first transistor to remain below its maximum rating even when the drain-source voltage exceeds the breakdown voltage. This intermediary structure enables high voltage operation without compromising device integrity.
2Strength
If a single transistor is designed for high breakdown voltage, then voltage withstand capability is improved, but the device complexity and manufacturing difficulty increase due to the square-law scaling of on-resistance
Solution Approach 1:
Instead of creating a single complex high-voltage transistor with inherently high on-resistance, the patent segments the function across two simpler transistors. The first transistor is optimized for voltage blocking with lower on-resistance requirements, while the second transistor is optimized for current conduction. This segmentation reduces the complexity of individual device structures compared to a single transistor designed to handle both high voltage and low resistance requirements.
Solution Approach 2:
The cascode configuration provides multi-functionality: the first transistor serves as the primary voltage-blocking element while the second transistor handles current conduction. The voltage divider circuit adds another layer of functionality by providing both gate voltage control and overvoltage protection. This multi-functional architecture achieves high breakdown voltage without requiring any single component to be overly complex.
3Strength
If the gate-source voltage of the first transistor is allowed to exceed its maximum rating during high voltage operation, then higher breakdown voltage is achieved, but the transistor may malfunction or be destroyed
Solution Approach 1:
The voltage divider circuit serves as an intermediary that indirectly couples the gate of the first transistor to the source of the second transistor. This indirect coupling allows the drain-source voltage to exceed the breakdown voltage while the voltage divider limits the gate-source voltage to remain below the maximum rating, preventing transistor malfunction or destruction during high voltage operation.
Solution Approach 2:
The voltage divider circuit provides beforehand cushioning by pre-establishing a voltage limitation mechanism that protects the first transistor's gate-source junction from exceeding its maximum rating. This protective structure is in place before any overvoltage event occurs, ensuring device integrity even when transient voltage spikes exceed the breakdown voltage.
Data Source
AI summary
A semiconductor power device may include a first power transistor configured to generate an output voltage. A semiconductor power device may include a second power transistor configured to receive an input voltage. The second power transistor is connected to the first power transistor in a cascode configuration. A semiconductor power device may include a voltage divider circuit connected to a gate terminal of the first power transistor and a source terminal of the second power transistor.