Current Limiting Circuit Thermal Matching

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing current limiting circuits for power supply semiconductors in automotive applications fail to accurately control overcurrents due to temperature variations, as they do not account for the temperature relationship between components like diode groups and sense resistors, leading to inaccurate current limitation and modulation by self-heating effects.

Innovation Solution

A current limiting circuit design where the sense resistor is disposed to surround the potential difference detection unit, ensuring that the temperatures of the sense resistor and diode groups are approximately equal, using a metal sense resistor with high heat conductivity to maintain consistent resistance and accurately control current flow despite temperature changes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the sense resistor is disposed separately from the potential difference detection unit, then the circuit layout is simpler, but the temperature difference between components causes inaccurate current limitation

Engineering Contradiction:

Improvecurrent limitation accuracyVSAvoidcomponent arrangement complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The sense resistor is disposed to surround the potential difference detection unit, merging the sensing function and temperature reference function into a single integrated structure. This ensures both components share the same temperature environment, eliminating temperature-induced measurement errors while maintaining a compact layout.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The sense resistor is positioned specifically to surround the potential difference detection unit, creating a localized thermal environment where both components experience identical temperature conditions. This local arrangement ensures accurate current measurement by compensating for temperature variations at the specific location where measurement occurs.

Inventive Principle:

Principle #3Local quality

2Measurement precision

If the sense resistor uses material with low heat conductivity, then manufacturing is easier, but self-heating effects modulate the current control accuracy

Engineering Contradiction:

Improvecurrent control accuracyVSAvoidself-heating energy loss

Core Design Contradiction:

Measurement precisionVSLoss of energy

Solution Approach 1:

The patent utilizes the self-heating effect of the sense resistor by surrounding the potential difference detection unit with it. The heat generated by the sense resistor warms the detection unit to the same temperature, converting the harmful self-heating into a beneficial temperature-matching mechanism that eliminates measurement errors due to temperature differences.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Adaptability or versatility

If the circuit does not compensate for temperature variations, then the device complexity is reduced, but the current limitation varies with temperature changes

Engineering Contradiction:

Improvetemperature range adaptabilityVSAvoidcurrent limitation stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The sense resistor serves dual functions: it senses the current through voltage drop measurement and simultaneously provides temperature compensation by surrounding the potential difference detection unit. The structure is self-sufficient, using its own heat to maintain temperature equilibrium with the detection unit, eliminating the need for external temperature compensation circuits.

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

The circuit effectively suppresses variations in output current limiting values by matching the temperature of the sense resistor with the diode groups and transistors, ensuring accurate current control through the output transistor even under temperature changes, thereby preventing damage from overcurrents.

Implementation Method 1

using a metal sense resistor with high heat conductivity to maintain consistent resistance and accurately control current flow despite temperature changes

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Data Source

PatentUS8879227B2Current limiting circuit

Publication Date: 2014.11.04 RENESAS ELECTRONICS CORP

AI summary

An exemplary aspect of the present invention is a current limiting circuit including: an output transistor that controls a current flowing to a load from a power supply; a current sense transistor through which a current dependent on a current flowing through the output transistor flows; a sense resistor connected in series with the current sense transistor; a potential difference detection unit that detects a potential difference generated between both ends of the sense resistor; a constant current generation unit that supplies a constant current to the potential difference detection unit; and a control unit that controls a conduction state of the output transistor based on a control voltage generated based on the potential difference and the constant current, in which the sense resistor is disposed so as to surround the potential difference detection unit.