Current-Limiting Circuit Parallel Path Transistor Protection
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Solution Overview
Problem
Current-limiting circuits experience high power losses and transistor overloading during short circuits, leading to potential destruction and undesirable sparking or heating in explosion-prone environments, with existing solutions either increasing costs or introducing time delays and complexity.
Innovation Solution
An additional high-ohmic current path is introduced in parallel to the transistor, utilizing a component with a diode characteristic and an auxiliary measuring resistor, which bypasses the transistor and increases the voltage drop seen by the shunt regulator during overcurrent events, reducing the transistor's current flow to prevent overloading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the transistor is dimensioned to handle maximum current during short circuits, then reliability is improved, but power loss increases and the transistor becomes overloaded during normal operation
Solution Approach 1:
The current path is segmented into two parallel paths: one through the transistor for normal operation and another through the auxiliary current path with the second shunt regulator for overcurrent protection. This segmentation allows the transistor to be optimized for normal operation without bearing the full burden of maximum short-circuit current, reducing power loss while maintaining reliability.
Solution Approach 2:
The auxiliary current path with the second shunt regulator acts as an intermediary that activates during overcurrent conditions. When the voltage across the measuring resistor exceeds the second reference voltage, the second shunt regulator conducts, creating an additional current path that limits the current through the transistor, thereby protecting it from overload without affecting normal operation.
2Reliability
If a thermocontroller is used to protect the transistor from overheating, then reliability is improved, but time delay is introduced and complexity increases
Solution Approach 1:
The auxiliary current path with the second shunt regulator is pre-configured in the circuit but remains inactive during normal operation. When overcurrent conditions occur, this pre-configured protection path automatically activates without requiring thermal sensing or control logic, providing immediate protection without time delay or increased complexity.
Solution Approach 2:
The mechanical thermocontroller that responds to thermal conditions is replaced by an electrical solution using the second shunt regulator that responds to voltage conditions. This substitution eliminates the time delay inherent in thermal response and removes the need for mechanical moving parts, simplifying the overall system while maintaining protection functionality.
3Productivity
If the transistor conducts maximum current during short circuits, then current limiting function is achieved, but the transistor becomes destroyed due to continuous overloading
Solution Approach 1:
The circuit dynamically adjusts the current path based on operating conditions. During normal operation, the transistor handles the full load current. During short-circuit conditions, when the voltage across the measuring resistor exceeds the second reference voltage, the second shunt regulator activates and dynamically shares the current burden, limiting the transistor current to safe levels while maintaining overall current limiting capability.
Solution Approach 2:
The auxiliary current path serves as a pre-prepared protective mechanism that cushions the transistor from destructive overcurrent conditions. The second shunt regulator and associated components are positioned and configured in advance to automatically engage when needed, absorbing the excess current and protecting the transistor without requiring any protective action during the actual overcurrent event.
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
This solution effectively reduces transistor power consumption during short circuits, preventing damage and allowing immediate return to normal operation without the need for maintenance, while maintaining safety and reducing overall power losses.
Implementation Method 1
a component connected reverse-biased and having a diode characteristic
Implementation Method 2
detects a voltage between its anode and its reference input and delivers a current correlated with the applied voltage to its cathode
Data Source
AI summary
A current-limiting circuit (100), which limits an electrical current from a voltage source to a consumer to a predetermined maximum current. A measuring resistor (110) is coupled into a current lead (103) between a circuit input (102) and a circuit output (104). A transistor (106) of the circuit is coupled into the current lead (103) with its collector-emitter path in series with the measuring resistor (110), and its base is connected to the current lead (103) through a series resistor (108). A shunt regulator (116) of the circuit has an anode, a reference input and a cathode, wherein the cathode is connected to the base of the transistor (106), and the anode and the reference input form a voltage tap across the measuring resistor (110). An additional, high-ohmic current path extends in parallel to the transistor (106) and includes a component connected reverse-biased having a diode characteristic and an auxiliary measuring resistor (120b), wherein the auxiliary measuring resistor (120b) is integrated in the voltage tap.