Rush Current Limiting Circuit for Power Conversion
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Solution Overview
Problem
Conventional rush current limiting circuits experience significant overshoot due to the rapid increase of rush current, requiring transistors with large current ratings, which hinders downsizing and increases noise emissions, especially in applications with steep power source voltage rises.
Innovation Solution
A rush current limiting circuit using a series circuit of an inductor and current detection resistor, where the second semiconductor switch controls the inter-output-terminal voltage to limit the rush current smoothly, allowing for the use of transistors with smaller current ratings and improving EMC performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transistor with a large current rating is used to withstand rush current, then the transistor can handle the rush current, but the product size increases and cost increases
Solution Approach 1:
The patent introduces a current limiting circuit as an intermediary component between the power source and the transistor. This circuit includes a current limiting transistor and a resistor that work together to limit the rush current before it reaches the main transistor, allowing the main transistor to have a smaller current rating while still protecting against rush current damage
Solution Approach 2:
The patent divides the current control function into two separate transistors: the main transistor for normal operation and a dedicated current limiting transistor for rush current protection. This segmentation allows each transistor to be optimized for its specific function, with the current limiting transistor being small and only active during transient conditions
2Reliability
If a rush current limiting circuit is added, then rush current is suppressed, but the circuit complexity increases
Solution Approach 1:
The patent merges the current limiting function with the existing transistor switching circuit by using the emitter of the current limiting transistor to connect to the base of the main transistor. This integration allows the current limiting function to be added without requiring completely separate circuitry, reducing overall complexity
Solution Approach 2:
The patent implements a feedback mechanism where a resistor monitors the current flowing through the current limiting transistor and adjusts its conduction accordingly. When rush current is detected, the feedback signal turns on the current limiting transistor, which automatically limits the current without requiring external control signals
3Measurement precision
If a resistor for detecting rush current is connected between the power source and the first transistor, then rush current can be detected, but a voltage difference is generated that reduces the base bias voltage
Solution Approach 1:
The patent applies local quality by placing the current detecting resistor specifically in the base circuit of the current limiting transistor, rather than in the main power path. This localized placement allows for accurate rush current detection while minimizing the impact on the overall circuit operation and base bias voltage
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 effectively limits rush currents without affecting steady-state current supply, enabling the use of smaller transistors and enhancing EMC performance, while eliminating the need for external power sources for control circuits, thus simplifying and weight-reducing vehicle harnesses.
Implementation Method 1
A rush current limiting circuit using a series circuit of an inductor and current detection resistor
Data Source
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AI summary
The present invention relates to a rush current limiting circuit in which a series circuit consisting of an inductor and a resistor for detecting a current is connected between a power source and a first semiconductor switch, in which there is provided a second semiconductor switch whose inter-output-terminal voltage is controlled by the voltage across the series circuit consisting of the inductor and the resistor for detecting a current, and in which the inter-output-terminal voltage of the second semiconductor switch controls the inter-control-terminal voltage of the first semiconductor switch so as to limit a current to a load; the present invention relates also to an electric power converter including the rush current limiting circuit.