Inrush Current Limiting Circuit Shutoff Failure Detection

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Solution Overview

Problem

Existing inrush current limiting circuits face challenges in detecting shutoff failures of subsidiary power switches without affecting the inrush current limiting characteristic, as the inrush current limiting resistor affects both the charging time constant and leak current measurement, making it difficult to monitor leak currents effectively.

Innovation Solution

Incorporating a diode connected in series with the subsidiary power switch to monitor the current flowing through it when both main and subsidiary switches are off, allowing for the detection of shutoff failures without interfering with the inrush current control characteristic, and using a monitoring circuit with an outputting section and detection judging section to determine if the current exceeds a threshold.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the inrush current limiting resistor is used to monitor leak current, then the leak current can be detected, but the inrush current control characteristic is affected

Engineering Contradiction:

Improveleak current detection accuracyVSAvoidinrush current control characteristic

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent divides the monitoring function from the inrush current limiting function by adding a separate monitoring circuit with its own resistor (Rm) and diode (Dm). This segmentation allows the inrush current limiting resistor (Rl) to focus on controlling inrush current while the separate monitoring components handle leak current detection, eliminating the interference between these two functions.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces a diode (Dm) as an intermediary component in the monitoring circuit. The diode allows current flow in one direction only, enabling the monitoring circuit to detect leak current through the inrush current limiting resistor without allowing the monitoring components to affect the inrush current control path. This intermediary element isolates the monitoring function from the control function.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of operation

If the semiconductor-switching device is used for the subsidiary power switch, then the switching timing can be easily controlled and size is reduced, but shutoff failure causing large leak current occurs

Engineering Contradiction:

Improveswitching timing controlVSAvoidshutoff failure resistance

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent implements a feedback mechanism by continuously monitoring the leak current through the diode and resistor combination. When the monitored current exceeds a predetermined threshold, the system detects shutoff failure and can take corrective action. This feedback loop enables early detection of semiconductor-switching device failures, allowing for timely intervention before catastrophic failure occurs.

Inventive Principle:

Principle #23Feedback

3Reliability

If the monitoring circuit is added to detect shutoff failure, then the failure detection capability is improved, but the circuit structure becomes more complex

Engineering Contradiction:

Improveshutoff failure detectionVSAvoidcircuit structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The monitoring circuit utilizes the existing inrush current limiting resistor and the natural operating conditions of the subsidiary power switch. By connecting the diode and monitoring resistor in parallel with the existing circuit components, the system achieves failure detection functionality without requiring complete redesign of the power supply circuit. The monitoring circuit serves itself by using the same current path that already exists during normal operation.

Inventive Principle:

Principle #25Self-service

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

Enables early detection of shutoff failures in the subsidiary power switch without compromising the inrush current control characteristic, allowing for timely intervention and maintaining vehicle performance by simplifying the circuit structure and improving leak current measurement accuracy.

Implementation Method 1

a diode connected in series with the subsidiary power switch to monitor the current flowing through it

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS7586727B2Inrush current limiting switching circuit for power supply

Publication Date: 2009.09.08 DENSO CORP

AI summary

An inrush current limiting power supply switching circuit is disclosed including a first switch through which an electrical load, having a capacitor, and a direct current power supply are connected, a second switch turned on prior to the first switch when supplying electric power from the direct current power supply to the electrical load, an inrush current limiting circuit connected in parallel to the first switch and having an inrush current limiting resistor connected to the second switch in series, and a monitoring circuit for monitoring a second-switch-shutoff leak current flowing through a diode, connected in series to the second switch in an orientation in which electric power is supplied, when both the first and second switches are off.