Protective Feedback Circuit for High Power Amplifier FETs
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Solution Overview
Problem
High-power and high-frequency amplifier circuits, particularly in plasma processing applications, face challenges in protecting field effect transistors (FETs) from destructive breakdowns due to over-voltage and impedance mismatches, leading to FET destruction during arc discharges in plasma chambers.
Innovation Solution
A protective feedback circuit is implemented, connecting the drain of the FET to a gate, utilizing avalanche diodes and capacitance to dissipate over-voltage energy quickly, and a switching diode to control the current path, ensuring the FET operates within safe voltage ranges and reducing the risk of avalanche breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high power FETs are used to withstand overvoltage by converting energy to heat, then the FET can handle higher power levels, but the FET may still be destroyed during arc discharge when reflected and incident voltage waves constructively superpose
Solution Approach 1:
The protective feedback circuit is activated before the FET can be destroyed by overvoltage. When the voltage between gate and drain exceeds a feedback threshold voltage, the circuit quickly reduces over-voltage energy at the drain within a few high-frequency periods, preventing the constructive superposition of reflected and incident voltage waves from destroying the FET.
Solution Approach 2:
The protective feedback circuit continuously monitors the voltage between gate and drain of the FET. When this voltage exceeds a predetermined feedback threshold voltage, the circuit automatically activates to reduce the over-voltage energy at the drain, creating a closed-loop protection mechanism that responds dynamically to overvoltage conditions.
2Strength
If FETs of higher drain voltage rating are used to withstand overvoltage, then the FET can handle higher voltages, but the solution is costly and place consuming
Solution Approach 1:
The protective feedback circuit acts as an intermediary between the FET and the overvoltage condition. Rather than relying solely on the FET's intrinsic voltage rating, the circuit intervenes to detect when voltage exceeds the feedback threshold and actively reduces over-voltage energy, protecting the FET from conditions that would otherwise require a higher voltage-rated device.
Solution Approach 2:
The protective feedback circuit dynamically changes the operating parameters of the FET by monitoring the gate-drain voltage and, when necessary, reducing the over-voltage energy at the drain. This allows the FET to operate safely at lower voltage ratings while still withstanding peak overvoltage conditions that would otherwise require higher-rated devices.
3Power
If more amplifiers with lower output power are combined to handle high power, then the voltage stress on each FET is reduced, but the device becomes more complex and occupies more space
Solution Approach 1:
The protective feedback circuit provides a universal protection mechanism that can be applied to single FET amplifiers of any power level. Rather than requiring multiple amplifiers to share the power load, the feedback circuit enables a single FET to safely handle high power by actively protecting it from overvoltage conditions, eliminating the need for complex multi-amplifier configurations.
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 protective feedback circuit effectively reduces over-voltage energy at the drain within a few high-frequency periods, preventing FET destruction and maintaining normal amplifier operation, even during impedance mismatches and arc discharges, thereby enhancing the robustness and reliability of the amplifier circuit.
Implementation Method 1
A protective feedback circuit is implemented, connecting the drain of the FET to a gate, utilizing avalanche diodes and capacitance to dissipate over-voltage energy quickly
Implementation Method 2
A protective feedback circuit is implemented, connecting the drain of the FET to a gate, utilizing avalanche diodes and capacitance to dissipate over-voltage energy quickly
Data Source
Figure 1
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AI summary
The invention describes an amplifier circuit for providing an output of at least 100 W, preferably of at least 200 W and most preferably of at least 250 W comprising a field effect transistor (111, 113). A drain of the field effect transistor (111, 113) is connected with a protective feedback circuit (400). The protective feedback circuit (400) is arranged to reduce an over-voltage energy at the drain of the field effect transistor (111, 113) if the voltage between the gate and a drain of the field effect transistor (111, 113) exceeds a feedback threshold voltage (355). The invention further describes a radio frequency amplifier comprising an amplifier circuit, an electrical radio frequency generator comprising the radio frequency amplifier and a plasma processing system comprising an electrical radio frequency generator. The invention finally describes a method of protecting a field effect transistor (111, 113) in an amplifier circuit.