Electronic Fuse Circuit Narrowing Trip and Limit Current Gap

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Solution Overview

Problem

Existing electronic fuse circuits (e-fuse) have a wide gap between the trip current (Itrip) and limited current (Ilim) thresholds, which can lead to undesirable operation where current delivery is terminated prematurely or not limited sufficiently in response to overcurrent conditions.

Innovation Solution

A circuit design incorporating a MOSFET power transistor, a MOSFET sense transistor, a differential amplifier circuit, a comparator circuit, and a switchable resistance or variable voltage generator to closely regulate the transition between triode and saturation modes of operation, thereby narrowing the gap between Itrip and Ilim.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a traditional fuse circuit is used to protect against overcurrent, then the load is protected from damage, but current delivery is completely terminated

Engineering Contradiction:

Improveload protectionVSAvoidcurrent delivery

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The circuit uses a sense transistor to continuously monitor the output current and feeds this information back to the differential amplifier, which adjusts the gate voltage of the power transistor to maintain current within safe limits while keeping the circuit operational

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The circuit dynamically adjusts the power transistor's conduction state based on real-time current conditions, transitioning between full conduction, current limiting, and shutdown states rather than using a static fuse mechanism

Inventive Principle:

Principle #15Dynamics

2Productivity

If an electronic fuse circuit reduces output current in response to overcurrent detection, then current delivery is maintained, but the gap between trip current and limited current is undesirably wide

Engineering Contradiction:

Improvecurrent deliveryVSAvoidcurrent threshold precision

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The differential amplifier dynamically changes the gate voltage parameter of the power transistor based on the sensed current, allowing precise control of the current limiting threshold and narrowing the gap between trip and limited current levels

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The circuit replaces the mechanical fuse with an electronic control system using transistors and amplifiers, enabling precise electronic adjustment of current thresholds rather than relying on fixed mechanical trip points

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS11467611B2Current limiting electronic fuse circuit

Publication Date: 2022.10.11 STMICROELECTRONICS SRL

AI summary

A power transistor generates an output current and a sense transistor generates a proportional sense current. A differential amplifier generates a gate voltage applied to the power and sense transistors in response to first and second input signals. A comparator circuit compares the gate voltage to a switching reference to detect whether the power and sense transistors are operating in a triode mode of operation or in a saturation mode of operation. At least one of the first and second input signals is modified in response to the detection made by the comparator circuit. In one instance, different reference voltages are applied to an input of the amplifier depending on the detected mode of operation. In another instance, different resistances are used to convert the sense current to a voltage for application to an input of the amplifier in response to the detected mode of operation.