Amplifying Transistor Input Current Limiting Against Excess Power
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Solution Overview
Problem
Conventional semiconductor devices are prone to destruction due to excessive electric power, particularly when used in high-frequency applications, leading to increased size, weight, and cost due to the need for magnetic isolators and large terminating resistors to manage high-frequency voltages and currents.
Innovation Solution
A semiconductor device incorporating a current limiting circuit connected to the input terminal of an amplifying transistor, which limits current to prevent excessive electric power from damaging the transistor, utilizing a protecting transistor and resistors to regulate current flow and prevent destruction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an isolator is connected to the output side of the amplifying transistor to prevent feedback destruction, then the reliability is improved, but the size and weight are increased
Solution Approach 1:
The patent extracts and eliminates the isolator component from the circuit by implementing current limiting directly at the input terminal of the amplifying transistor. This removes the need for the isolator while maintaining protection against excessive power, thereby reducing device size and weight.
Solution Approach 2:
The current limiting circuit is placed at the input terminal to preemptively limit current before it can cause damage. This preliminary action prevents excessive power from reaching the amplifying transistor in the first place, eliminating the need for downstream protective components like isolators.
2Reliability
If an isolator is used to treat large electric power, then the reliability is improved, but the costs are increased
Solution Approach 1:
The patent removes the isolator component and replaces it with a current limiting circuit implemented at the input terminal. This substitution eliminates the need for expensive magnetic components while maintaining protection functionality, thereby reducing manufacturing costs.
Solution Approach 2:
The current limiting circuit uses simple, inexpensive components (resistors and transistors) rather than expensive magnetic isolators. This approach prioritizes cost-effective protection through readily available components.
3Reliability
If the size of terminating resistors is enlarged to improve heat dissipation, then the reliability is improved, but the weight is increased
Solution Approach 1:
The current limiting circuit preemptively restricts current flow before excessive power can generate harmful heat. This preliminary current limitation reduces the thermal load on terminating resistors, allowing them to be smaller while maintaining reliability.
4Device complexity
If conventional resistors are used without current limiting, then the device complexity is reduced, but the reliability is worsened due to destruction from excessive power
Solution Approach 1:
The current limiting circuit is implemented at the input terminal to preemptively control current flow. This early intervention protects downstream components including simple resistors from excessive power, maintaining both simplicity and reliability.
Data Source
AI summary
A current limiting circuit is connected to the gate (input terminal) of an amplifying transistor. The current limiting circuit includes a protecting transistor, a first protecting resistor connecting the drain to the gate of the protecting transistor, and a second protecting resistor connecting the source to the gate of the protecting transistor. The current limiting circuit limits current, so that electric power larger than the maximum electric power allowable for the amplifying transistor does not pass.