Output Driver Circuit Overcurrent Protection via Current Mirror
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Solution Overview
Problem
Conventional output driver circuits with overcurrent protection functions require a comparator and reference voltage circuit, leading to a large circuit scale and deterioration of drive capability due to the need for a sense resistor connected to the output driver's source.
Innovation Solution
An output driver circuit with an open-drain configuration, utilizing a constant-current circuit, a constant-current mirror MOS transistor, and a selector circuit to control the current of an output MOS transistor, eliminating the need for a sense resistor and comparator, thereby simplifying the circuit configuration and maintaining drive capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a comparator and reference voltage circuit are used for overcurrent protection, then overcurrent protection function is achieved, but circuit scale increases
Solution Approach 1:
The patent extracts the overcurrent protection function from the complex comparator-based control system and implements it through a simple current mirror circuit mechanism. The current mirror inherently limits output current without requiring external comparison logic, thus achieving protection while minimizing circuit scale.
Solution Approach 2:
The current mirror circuit automatically regulates the output current through its inherent feedback mechanism. When the output current exceeds the mirror current, the output transistor naturally enters saturation, self-limiting the current without external intervention from comparators or control logic.
2Reliability
If a sense resistor is connected to the source of the output driver, then overcurrent protection is achieved, but drive capability deteriorates
Solution Approach 1:
The patent removes the sense resistor from the source path of the output driver and instead uses the current mirror circuit to establish the current limit. This extraction eliminates the resistive degradation of drive capability while preserving the overcurrent protection function through the mirror's inherent current regulation.
Solution Approach 2:
The current mirror acts as an intermediary mechanism that indirectly controls the output current without inserting a sense resistor in the signal path. The mirror current serves as the reference that automatically limits the output driver current, avoiding the power loss and drive capability deterioration associated with source resistors.
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 provides effective overcurrent protection with a simple circuit configuration that does not degrade the output driver's performance, ensuring reliable operation without the need for additional components like sense resistors or reference voltage circuits.
Implementation Method 1
a constant-current circuit which supplies a constant current; a constant-current mirror MOS transistor which generates a voltage based on the constant current
Implementation Method 2
an output MOS transistor with a gate thereof connected to an output terminal of the selector circuit, a drain thereof connected to an output terminal of the output driver circuit and a source thereof connected to the first supply terminal, wherein a current flowing between the source and the drain of the output MOS transistor is limited by a voltage based on the constant current
Data Source
AI summary
An output driver circuit provides an overcurrent protection function by a simple circuit configuration. The output driver circuit has a constant-current circuit, a constant-current mirror MOS transistor, and a selector circuit. The constant-current mirror MOS transistor and the output MOS transistor constitute a current mirror circuit. The gate of the output MOS transistor is controlled by a voltage based on a constant current generated by the constant-current mirror MOS transistor, thereby limiting the current flowing between the source and the drain of the output MOS transistor.