Composite Semiconductor Device Transistor Selection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing composite semiconductor devices with normally on and normally off type transistors connected in series face instability in control due to electric charge leakage during the turned-off state of the second field effect transistor, leading to potential breakdown.
Innovation Solution
The selection of transistors based on specific capacitance ratios and formulas, such as Coss > Cds * Vds / Vbr, ensures that the drain voltage of the second transistor remains below the breakdown voltage, preventing breakdown without the need for additional stabilizing devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Zener diode is connected between the drain and source of the second field effect transistor to limit the drain-source voltage, then the breakdown of the second transistor is prevented, but the control becomes unstable due to electric charge leakage during the turned-off state
Solution Approach 1:
A capacitor is introduced as an intermediary element connected between the gate and source of the second field effect transistor. This capacitor acts as a mediator that stabilizes the gate-source voltage by filtering out voltage fluctuations caused by charge leakage, thereby maintaining control stability while the Zener diode continues to protect against breakdown.
Solution Approach 2:
The capacitor is configured to compensate for electric charge leakage before it can cause significant control instability. By storing electrical energy in advance, the capacitor provides a cushioning effect that maintains stable gate voltage even when charge leakage occurs during the turned-off state of the second transistor.
2Power
If a field effect transistor of normally on type is used in a semiconductor device, then high breakdown voltage and high-speed switching are achieved, but conventional gate drive circuits cannot be used and additional control mechanisms are required
Solution Approach 1:
The invention merges the protective and stabilizing functions into a single integrated structure by connecting the Zener diode and capacitor in a specific configuration. This combined approach allows the normally on transistor to operate with high breakdown voltage while the integrated Zener-capacitor network provides both breakdown protection and control stability without requiring separate complex gate drive circuits.
Solution Approach 2:
The Zener diode and capacitor configuration enables the transistor to self-regulate its operation. The Zener diode automatically clamps the drain-source voltage when breakdown is approached, and the capacitor automatically compensates for charge leakage, eliminating the need for external active gate drive control mechanisms.
Data Source
AI summary
In a composite semiconductor device which is provided with a normally-on-type first transistor and a normally-off-type second transistor which are serially connected, the second transistor is selected so as to satisfy Formula (1):Coss>CdsVdsVbr-Cds-Cgs(1)In this regard: Coss: output capacitance of second transistor Cds: drain to source capacitance of first transistor Cgs: gate to source capacitance of first transistor Vds: power supply voltage Vbr: breakdown voltage of second transistor.