Selectable Current Limiter Circuit for Amplifiers
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current current limiting circuits in amplifiers are susceptible to performance variations due to temperature and process changes, leading to inaccurate current limitation and potential operational breakdowns, especially in high voltage or current applications.
Innovation Solution
The implementation of a set resistor and reference resistors configured to track each other, with limiter circuits that compare a voltage reference to the output voltage across a limiting resistor to maintain current within set limits, using operational amplifiers and differential transistor pairs to sink or source current as needed, ensuring constant voltage drops across reference resistors and accurate current limiting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Vbe-based current limiting circuits are used, then current limiting function is achieved, but performance varies widely over temperature and process changes
Solution Approach 1:
The patent changes the reference parameter from Vbe voltage (which has negative temperature coefficient) to a bandgap voltage reference that maintains constant voltage across temperature variations. This parameter change eliminates the temperature dependency issue inherent in Vbe-based circuits while preserving the current limiting function.
Solution Approach 2:
The patent uses matched transistor pairs (Q1-Q2 and Q3-Q4) that are geometrically identical and positioned close together to ensure they experience the same process variations. This copying approach causes the process-induced mismatches to cancel out, improving both accuracy and stability over temperature and process changes.
2Adaptability or versatility
If selectable current limits are required, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent segments the current limiting function into multiple independent branches, each with its own current setting resistor (R1-R4) and transistor pair. This segmentation allows each branch to be independently configured for different current limits while sharing common circuitry, achieving adaptability without proportionally increasing overall complexity.
Solution Approach 2:
The patent creates a universal current limiting circuit structure where the same basic topology (voltage reference, current mirror, sensing transistor) serves multiple current limiting functions simultaneously. By making the circuit multi-functional, selectable current limits are achieved without requiring separate dedicated circuits for each limit level.
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 provides accurate and stable current limiting across temperature and process variations, preventing operational breakdowns and maintaining current within specified limits, while minimizing power wastage and resource usage.
Implementation Method 1
The first and second reference resistors are configured to substantially track the set resistor, such that each of the voltage drops across the first and second reference resistors is substantially constant
Implementation Method 2
limiter circuits that compare a voltage reference to the output voltage across a limiting resistor to maintain current within set limits
Implementation Method 3
using operational amplifiers and differential transistor pairs to sink or source current as needed, ensuring constant voltage drops across reference resistors and accurate current limiting
Data Source
AI summary
A selectable current limiter circuit to limit the current an amplifier with a load. The limiter circuit limits the current of an amplifier by comparing a voltage reference that follows the output swing of the amplifier to voltage drop across a current limiting resistor coupled to the output of the amplifier. The limiter circuits are operatively coupled to buffer and switch circuits that delay the current limiting until the limiter circuits are activated.