Current Limiting Circuit Reference Voltage Feedback Control
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Solution Overview
Problem
Current limiting circuits face instability when output pin voltages drop low relative to reference voltages, causing the ratio between main and sense transistors to become skewed, leading to output currents exceeding the programmed current limit.
Innovation Solution
A current limiting apparatus that controls the reference voltage as a function of the output voltage, using a first field effect transistor, a sense transistor, amplifiers, and resistors to maintain a common voltage potential and ensure the current output remains at or below the programmed current limit by adjusting the reference voltage based on output voltage changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the output pin voltage drops low relative to reference voltage, then the circuit operation continues, but the ratio between main and sense transistors becomes skewed causing output current to exceed programmed current limit
Solution Approach 1:
The patent implements a feedback mechanism where the output voltage is continuously monitored and used to dynamically adjust the reference voltage. When output voltage drops, the reference voltage is automatically reduced through a feedback circuit, preventing the transistor ratio skew that would otherwise cause current limit violations. This closed-loop control ensures current accuracy is maintained across varying output conditions.
Solution Approach 2:
The patent dynamically changes the reference voltage parameter based on output voltage conditions. By making the reference voltage variable rather than fixed, the system adapts to different output voltage levels and maintains proper transistor ratios. This parameter adjustment prevents current limit inaccuracies while allowing continuous circuit operation.
2Device complexity
If the reference voltage is kept fixed, then the circuit design is simple, but the current limit accuracy deteriorates when output voltage varies
Solution Approach 1:
A feedback circuit monitors output voltage and automatically adjusts the reference voltage to maintain current limit accuracy. This feedback mechanism adds minimal complexity while significantly improving precision across varying output conditions.
Solution Approach 2:
The reference voltage is transformed from a static fixed value to a dynamic value that automatically adapts to output voltage changes. This dynamic adjustment maintains transistor ratio accuracy without requiring complex external calibration or adjustment mechanisms.
3Stability of the object's composition
If the transistor ratio is maintained fixed, then the circuit structure is stable, but the current limit accuracy worsens when output conditions change
Solution Approach 1:
Rather than changing the physical transistor ratios, the patent changes the electrical parameter (reference voltage) that controls the effective current limit. This maintains the stability of the transistor structure while achieving accurate current limiting under varying output conditions through parameter adaptation.
Data Source
AI summary
An example current limiting apparatus comprises a first transistor to carry a first current; a sense transistor coupled to the first transistor, the sense transistor to carry a sense current that is a function of the first current; a first amplifier coupled to the first transistor and the sense transistor, the amplifier to achieve a common voltage potential on terminals of the first and the sense transistors; a second amplifier coupled to the first amplifier and the sense transistor, the second amplifier to control the first and sense transistors based on the sense current; and a circuit coupled to the first and second amplifiers, the circuit to control an input to the second amplifier based on an input to the first amplifier such that a current limit of the first transistor remains below a programmed current limit of the first transistor.