Output Circuit Current Limiting for Ground Short Protection

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Solution Overview

Problem

Existing semiconductor output circuits face challenges in managing short circuits to ground, leading to increased current flow before interruption, which enlarges circuit scale and increases costs due to the need for wider interconnects and more output transistors in parallel, compromising safety and efficiency.

Innovation Solution

An output circuit design that initiates operation in a constant-current drive state, limiting output current to a predetermined value, and shifts to a normal drive state only if a short circuit to ground occurs, using a constant-current limiting circuit and output-voltage comparison circuit to control the output current based on voltage levels, preventing high current flow during short circuits.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional overcurrent protection circuits are used that allow high current flow before interruption, then the circuit can handle short circuits, but the circuit scale enlarges and costs increase due to wider interconnects and more transistors

Engineering Contradiction:

Improveshort circuit protection capabilityVSAvoidcircuit scale

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The circuit performs preliminary action by detecting voltage drops across the output transistor before excessive current can flow. The VDS detection circuit continuously monitors the drain-source voltage and triggers protection before the short circuit current can cause damage, eliminating the need for oversized interconnects and transistors that would be required if the circuit had to withstand high fault currents.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent replaces the mechanical/physical approach of using larger transistors and wider interconnects to handle fault currents with an electrical detection and control system. Instead of relying on physical robustness to withstand short circuit currents, the circuit uses voltage detection and transistor control to prevent excessive current flow, thereby reducing the physical scale of components.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If the output transistor is designed to withstand high short circuit currents, then protection is provided, but the transistor size and interconnect width must increase

Engineering Contradiction:

Improveshort circuit withstanding capabilityVSAvoidinterconnect width

Core Design Contradiction:

ReliabilityVSLength of stationary object

Solution Approach 1:

The patent replaces the mechanical approach of using wider interconnects to handle fault currents with an electrical detection and control system. The VDS detection circuit monitors voltage drops and triggers protection before excessive current can flow, eliminating the need for physically robust interconnects that would be required to withstand high fault currents.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The circuit performs preliminary action by detecting voltage drops across the output transistor before excessive current can flow. The continuous monitoring of VDS allows the protection mechanism to activate before the short circuit current can cause damage, thereby allowing the use of narrower interconnects that would not need to withstand high fault currents.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If more output transistors are used in parallel to handle short circuits, then protection capability is improved, but device complexity and manufacturing cost increase

Engineering Contradiction:

Improveshort circuit protection capabilityVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent replaces the approach of using multiple parallel transistors to handle fault currents with an electrical detection and control system. The VDS detection circuit and transistor control mechanism prevent excessive current flow, allowing the use of fewer, smaller transistors that are less expensive to manufacture while providing equivalent or superior protection capability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The circuit performs preliminary action by detecting voltage drops and triggering protection before excessive current can flow. This prevents the need to design transistors to withstand high fault currents, allowing the use of fewer, smaller, and less expensive transistors that would not need to be rated for high-stress conditions.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9474124B2Output circuit

Publication Date: 2016.10.18 RENESAS ELECTRONICS CORP

AI summary

There is provided an output circuit for supplying an output current to a load coupled to an output terminal in response to an input signal. The output circuit includes an output transistor for supplying the output current to the output terminal, an output-drive circuit for driving the output transistor, a constant-current limiting circuit for generating a current control signal for limiting the output current to a predetermined current value, and a control circuit for implementing a control such that the output current is controlled on the basis of the current control signal if a voltage at the output terminal is at a predetermined voltage, or less after the input signal is supplied while the output transistor is driven by the output-drive circuit if the voltage at the output terminal is in excess of the predetermined voltage.