MOSFET Protection Circuit for Reverse Polarity Overcurrent Blocking
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Solution Overview
Problem
Existing protection circuits for integrated circuits face challenges in managing excessive current due to reverse polarity supply voltages, particularly in in-vehicle electronic devices where high gate withstand voltages are required to prevent overcurrents.
Innovation Solution
A protection circuit design utilizing p-type field effect transistors (FETs) with gate drives that adjust voltages to ensure parasitic diodes are in an off state, regardless of supply voltage polarity, reducing the gate withstand voltage and preventing overcurrents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protection circuit uses p-type MOSFETs with bulk connected to a higher voltage terminal to keep parasitic diodes off, then overcurrent prevention is improved, but the gate withstand voltage requirement increases
Solution Approach 1:
The protection circuit is divided into multiple p-type MOSFETs (first, second, and third transistors) with distinct functions: the first and second transistors control current paths from supply and ground terminals respectively, while the third transistor acts as a main protection switch. This segmentation allows each transistor to operate within lower voltage stress while collectively providing robust overcurrent protection.
Solution Approach 2:
The patent introduces a new control dimension by connecting the bulk of each transistor to a common node rather than directly to supply or ground terminals. This dimensional change in voltage reference allows the parasitic diodes to remain reverse-biased through a different voltage distribution mechanism, reducing the gate-source voltage stress while maintaining protection functionality.
2Reliability
If the bulk voltage is kept at the higher of supply or ground voltage to reverse bias parasitic diodes, then protection against reverse polarity is improved, but the voltage stress on transistor gates increases
Solution Approach 1:
A common node is introduced as an intermediary voltage reference point to which the bulks of all p-type MOSFETs are connected. This intermediary structure mediates the voltage distribution such that the parasitic diodes remain reverse-biased during reverse polarity conditions without subjecting the gate terminals to excessive voltage stress, as the bulk voltage is decoupled from direct connection to supply or ground terminals.
3Reliability
If high gate withstand voltage transistors are used to handle potential reverse voltage, then protection capability is improved, but device complexity and cost increase
Solution Approach 1:
The patent changes the voltage parameters in the protection circuit by using a common node voltage reference system instead of direct supply/ground connections. This parameter change allows standard p-type MOSFETs with lower gate withstand voltage ratings to be used, as the voltage distribution is optimized to keep gate-source and gate-drain voltages within safe operating limits while maintaining effective reverse polarity protection.
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 effectively prevents overcurrents by ensuring parasitic diodes are in an off state, reducing the gate withstand voltage requirements and enhancing the reliability of the circuit, even under abnormal voltage conditions.
Implementation Method 1
a first transistor (M1) including a gate (G1) and a bulk (NB1), and being a p-type field effect transistor (FET)
Implementation Method 2
a parasitic diode that is formed between the bulk (N well) of each of the transistors M11 to M13 and a P-type region (P well or the like) in contact with the bulk
Data Source
AI summary
A first gate drive outputs a first drive voltage to turn a first transistor on upon occurrence of a condition in which a voltage at a supply terminal is higher than a voltage at a ground terminal, the output first drive voltage being higher than the voltage at the ground terminal. A second gate drive outputs a second drive voltage to turn a second transistor on, upon occurrence of a condition in which the voltage at the supply terminal is lower than the voltage at the ground terminal, the output second drive voltage being higher than the voltage at the supply terminal.