Back-to-Back MOSFET Current Sensing Without Isolation Interfaces
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Solution Overview
Problem
Current sensing in back-to-back MOSFET configurations is challenging due to increased circuit complexity and cost, and the need for isolation interfaces, which can affect accuracy, response time, and bandwidth.
Innovation Solution
The proposed apparatus includes a first and second MOSFET in a back-to-back configuration, a gate driver circuit, a shunt resistor between the source terminals of the MOSFETs, and return resistors with higher resistance than the shunt resistor, allowing effective current sensing without increasing circuit complexity or cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current sensing is implemented in back-to-back MOSFET configuration using conventional methods, then current sensing capability is achieved, but circuit complexity and cost increase
Solution Approach 1:
A shunt resistor is introduced as an intermediary component connected to the common source terminal of the back-to-back MOSFETs. This shunt resistor provides a dedicated current sensing path that allows accurate measurement of the current flowing through both MOSFETs without requiring complex sensing circuits or isolation interfaces, thereby maintaining low circuit complexity while achieving precise current sensing.
2Measurement precision
If isolation interfaces are added for current sensing, then sensing accuracy is improved, but response time and bandwidth are degraded
Solution Approach 1:
The patent extracts the current sensing function from the main power circuit by using a separate shunt resistor connected to the common source terminal. This extraction allows the sensing circuit to operate independently without requiring isolation interfaces between the high-voltage power path and the low-voltage sensing path, thereby maintaining both high sensing accuracy and fast response time without the bandwidth limitations imposed by isolation components.
3Measurement precision
If shunt resistor is placed between drain and high voltage source, then current sensing is achieved, but circuit complexity and cost increase
Solution Approach 1:
The shunt resistor is strategically placed at the common source terminal where it serves multiple functions: it senses the current flowing through both back-to-back MOSFETs, provides a reference point for the sensing circuit, and does not require additional isolation or protection components. This multi-functional placement reduces the overall component count and circuit complexity compared to placing the shunt resistor in the high-voltage drain path, thereby reducing manufacturing cost while maintaining sensing capability.
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 enables accurate and efficient current sensing in back-to-back MOSFET configurations, maintaining low circuit complexity and cost while preserving bandwidth and response time.
Implementation Method 1
an operational amplifier coupled to the shunt resistor to detect a voltage drop across the shunt resistor so as to detect current through the shunt resistor
Implementation Method 2
a first MOSFET return resistor coupled between the source terminal of the first MOSFET and the return terminal of the gate driver circuit. The resistance of the first MOSFET return resistor may be greater than the resistance of the shunt resistor
Data Source
AI summary
An apparatus for sensing current in a back-to-back MOSFET configuration is provided. The apparatus may include a first MOSFET having a gate terminal, a drain terminal, and a source terminal, a second MOSFET having a source terminal coupled to the source terminal of the first MOSFET, a gate terminal, and a drain terminal, a gate driver circuit including at least one gate drive output terminal to output a gate drive signal to the gate terminals of the first and second MOSFETs, and a return terminal coupled to the source terminals of the first and second MOSFETs, a shunt resistor coupled between the source terminals of the first and second MOSFETs, and a first MOSFET return resistor coupled between the source terminal of the first MOSFET and the return terminal of the gate driver circuit. The first MOSFET return resistor resistance may be greater than a resistance of the shunt resistor.