MOSFET Switch Circuit for Bidirectional Current Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing switch circuits with current sensing functionality suffer from conduction loss, increased component area and cost, and complexity due to parallel resistor configurations, particularly in high-power applications, and are limited to sensing unidirectional currents.
Innovation Solution
A switch circuit design incorporating a first and second switch with a current sensing circuit that includes a third switch and error amplifier circuits to generate a sensing voltage proportional to the switch current, capable of sensing both positive and negative currents without parallel resistors, using MOSFETs and current mirrors to achieve bidirectional current sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sensing resistor is used for current sensing, then current magnitude can be measured, but conduction loss increases and system efficiency decreases
Solution Approach 1:
The patent creates a copy of the main switch (third switch Q3) with identical gate-source voltage characteristics. This copy switch generates a proportional current (third switch current) that mirrors the main switch current without bearing the full burden of current conduction, thereby enabling accurate sensing with minimal power loss.
Solution Approach 2:
The error amplifier circuit acts as an intermediary that compares the drain voltages of the first and third switches and generates a feedback signal to control the third switch's current. This intermediary mechanism enables indirect current measurement without requiring the sensing path to carry the full main current, reducing conduction losses.
2Measurement precision
If parallel resistors are used for high-current sensing, then current measurement capability increases, but component area and cost increase
Solution Approach 1:
The patent changes the sensing approach from direct resistive sensing to transistor-based current mirroring. By utilizing the third switch's current characteristics and the error amplifier's voltage control, the system achieves high-current sensing capability through parameter transformation rather than scaling up resistor values or using parallel resistor configurations.
3Measurement precision
If parallel resistors are used for high-current sensing, then current measurement capability increases, but circuit complexity increases
Solution Approach 1:
The patent merges the current sensing function with the existing switch control circuitry. The third switch Q3 is integrated into the same gate control network as the first switch, and the error amplifier utilizes the existing drain voltage nodes. This merging eliminates the need for separate sensing resistors and their associated complex parallel configurations, simplifying the overall circuit while maintaining high-current sensing capability.
4Device complexity
If unidirectional sensing is implemented, then circuit design is simplified, but bidirectional current control capability is lost
Solution Approach 1:
The error amplifier circuit serves multiple functions: it controls the third switch current to track the main switch current, generates the sensing output voltage, and inherently supports bidirectional operation. The feedback mechanism automatically adapts to current direction changes, providing universal current sensing capability for both positive and negative current flows without requiring separate sensing paths.
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
Reduces conduction loss, component area, and cost while improving system efficiency by accurately sensing both positive and negative currents, thus simplifying circuit design and enhancing performance in high-power applications.
Implementation Method 1
a first error amplifier circuit, configured to control a drain voltage of the third switch to track a drain voltage of the first switch through feedback control, such that the third switch current is positively correlated with the first switch current
Implementation Method 2
a current-to-voltage conversion circuit, configured to generate a sensing voltage based on the third switch current, wherein the sensing voltage is positively correlated with the first switch current
Data Source
AI summary
A switch circuit with current sensing functionality includes: a first and second switch, coupled between a first and second terminal of the switch circuit, and configured to control a conductive state between the first and second terminal according to a control signal; and a current sensing circuit configured to sense a first switch current flowing through the first switch. The current sensing circuit includes: a third switch, a gate and a source of the third switch being coupled in parallel with the first switch to generate a third switch current; a first error amplifier circuit configured to control a drain voltage of the third switch to track a drain voltage of the first switch through feedback, thereby making the third switch current positively correlated to the first switch current; and a current-to-voltage conversion circuit configured to generate a sensing voltage based on the third switch current.