JFET Current Limiter With TVS Shunt for Fault Current Handling
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing current limiting devices, such as current limiting diodes, suffer from high steady-state losses and large size due to the need for multiple parallel-connected JFETs to achieve desired ratings, and they may not provide continuous current during fault conditions.
Innovation Solution
A current limiting device comprising a primary current path with a JFET and a secondary current path with a Transient Voltage Suppressor (TVS) that activates above a threshold current, shunting excess current away from the primary limiter, reducing the need for high-rated JFETs and minimizing steady-state losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple parallel-connected JFETs are used to achieve desired current ratings, then the current handling capability is improved, but the device size and mass increase
Solution Approach 1:
The current limiting device is segmented into two distinct functional paths: a primary current path with a first JFET for normal operation, and a secondary current path with a second JFET for fault conditions. This segmentation allows each JFET to be individually rated for specific current levels, eliminating the need for multiple parallel JFETs and reducing overall device size and mass.
2Power
If multiple parallel-connected JFETs are used to achieve desired current ratings, then the current handling capability is improved, but the device complexity increases
Solution Approach 1:
The device is divided into primary and secondary current paths with distinct JFETs, each optimized for specific operating conditions. This functional segmentation simplifies the overall design by assigning dedicated components to specific tasks rather than requiring multiple general-purpose parallel JFETs.
Solution Approach 2:
The device dynamically switches between primary and secondary current paths based on operating conditions. During normal operation, current flows through the primary path; during fault conditions, current automatically transitions to the secondary path. This dynamic behavior enables a single device to handle varying current requirements without increasing structural complexity.
3Loss of energy
If a current limiting diode with source resistor is used, then the current limiting function is achieved, but steady-state losses increase
Solution Approach 1:
The device dynamically adjusts its resistance based on operating conditions. During normal steady-state operation, the primary JFET maintains low resistance for minimal power losses. During fault conditions, the secondary JFET activates to provide current limiting. This dynamic resistance adjustment eliminates the continuous steady-state losses associated with fixed source resistors in conventional current limiting diodes.
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 solution provides a compact, low-loss current limiting device capable of handling high fault currents while maintaining continuous current supply, reducing the size and mass of the device and minimizing steady-state losses.
Implementation Method 1
If the current flowing between the source terminal (S) and drain terminal (D) increases, the magnitude of the voltage across the source resistor also increases, which in turn increases the magnitude of the gate voltage of the JFET. The increase in gate voltage magnitude reduces the size of the conduction channel of the JFET, increasing its electrical resistance.
Implementation Method 2
when the current flowing through the primary current path passes a threshold, the voltage drop across the primary current limiter passes a breakdown voltage of the TVS
Data Source
Figure 1A~1B
Figure 2~3
Figure 4A~4C
AI summary
A current limiting device 100, 100a, 100b and an electrical power system 10a, 10b comprising a current limiting device 100, 100a, 100b are provided. The current limiting device 100, 100a, 100b comprises: a primary current path 110 extending between a first node N1 and a second node N2 and having a primary current limiter 111 connected therein, the primary current limiter 111 comprising at least one JFET 101, 1011-N; and a secondary current path 120 extending between the first node N1 and the second node N2 in parallel with the primary current path 110, the secondary current path 120 comprising a Transient Voltage Suppressor (TVS) 121. The primary current limiter 111 is configured so that a voltage drop across the primary current limiter 111 increases as a current flowing through the primary current path 110 increases. When the current flowing through the primary current path 110 passes a threshold, the voltage drop across the primary current limiter 111 passes a breakdown voltage of the TVS 121.