Overcurrent Detection Circuit Early Effect Cancellation
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Solution Overview
Problem
Conventional overcurrent detection circuits suffer from reduced accuracy due to the early effect in current mirror circuits, which affects the correct detection of overcurrent conditions in MOS transistors connected in series with electrical loads, and are prone to instability and incorrect operation when the load current is high or when there are potential differences between ground connections.
Innovation Solution
An overcurrent detection circuit with an early effect cancel circuit that includes a pair of transistors interposed between the current mirror circuit and a resistor, ensuring that the current flowing through the resistor is equal to the current flowing through the detection transistor, thereby maintaining accurate overcurrent detection even when the early effect occurs, and utilizing level shift diodes and reverse current protection diodes to stabilize the circuit operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional current mirror circuit is used for overcurrent detection, then the circuit structure is simple, but the detection accuracy is reduced due to the early effect
Solution Approach 1:
An early effect cancel circuit is introduced as an intermediary component between the current mirror circuit and the detection transistor. This circuit includes a pair of transistors configured to cancel the early effect, thereby improving detection accuracy without significantly complicating the overall circuit structure
Solution Approach 2:
The invention changes the electrical parameters of the circuit by introducing transistors with specific characteristics that compensate for the early effect. By adjusting the transistor sizing and configuration in the early effect cancel circuit, the detection accuracy is improved while maintaining circuit simplicity
2Reliability
If the load current is high or ground potential differences exist, then the circuit may operate incorrectly, but adding protection circuits increases complexity
Solution Approach 1:
The circuit incorporates protection mechanisms that are activated beforehand to prevent incorrect operation. Reverse current protection diodes and level shift diodes are positioned to preemptively protect against high load currents and ground potential differences, ensuring reliable operation without requiring complex real-time protection circuits
Solution Approach 2:
The invention converts potentially harmful effects (early effect, ground potential differences) into manageable parameters. By designing the early effect cancel circuit to specifically counteract the early effect, and using diodes to manage ground potential differences, the circuit transforms these adverse factors into controlled conditions that enhance overall reliability
Data Source
AI summary
An overcurrent detection circuit for detecting an overcurrent condition in an output transistor connected in series with an electrical load includes a pair of transistors having input terminals connected together. The pair of transistors is interposed between a current mirror circuit and a resistor and between the current mirror circuit and a detection transistor capable of being turned on at the same time as the output transistor. When a voltage is applied to the input terminals of the pair of the transistors, output terminals of the current mirror circuit are fixed at the same potential. Thus, even when an early effect occurs in the current mirror circuit, an electric current flowing through the resistor becomes equal to that flowing through the detection transistor. The overcurrent detection circuit can accurately detect the overcurrent condition based on a voltage drop across the resistor.