Programmable Overcurrent Protection for Switch Temperature Compensation

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Solution Overview

Problem

Existing overcurrent protection circuits in switch-mode power supplies fail to accurately detect overcurrent events across varying temperatures due to the temperature-dependent on-resistance of FET switches, leading to potential damage from inductor saturation.

Innovation Solution

An overcurrent protection circuit that generates an adjustable overcurrent threshold level based on the temperature coefficient of the switch, matching the on-resistance variation, ensuring precise detection of overcurrent conditions across a range of temperatures by using an adjustable voltage generator and detection circuit.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a fixed overcurrent threshold is used in the protection circuit, then the circuit structure is simple, but the overcurrent detection accuracy deteriorates with temperature variations

Engineering Contradiction:

Improveprotection circuit structureVSAvoidovercurrent detection accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent implements a dynamic overcurrent threshold that automatically adjusts with temperature changes. The threshold voltage is generated by a temperature-dependent voltage source that tracks the FET's on-resistance variations, ensuring accurate overcurrent detection across all operating temperatures without requiring complex fixed-threshold circuits.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the threshold parameter from a fixed value to a temperature-dependent variable. By making the overcurrent threshold track the temperature coefficient of the FET's on-resistance, the detection accuracy is maintained across temperature variations while keeping the circuit implementation relatively simple.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If the overcurrent threshold is adjusted to match temperature variations, then the overcurrent detection accuracy is improved, but the device complexity increases

Engineering Contradiction:

Improveovercurrent detection accuracyVSAvoidprotection circuit structure

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The protection circuit uses the temperature coefficient of the FET's on-resistance to automatically generate the appropriate threshold voltage. The circuit self-adjusts by leveraging the inherent temperature-dependent properties of the FET, eliminating the need for external temperature sensors or complex adjustment mechanisms.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent introduces a voltage source with a temperature coefficient that matches the FET's on-resistance temperature coefficient as an intermediary. This voltage source acts as a mediator that translates temperature changes into the corresponding threshold voltage adjustments, simplifying the overall circuit design.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Power

If current through the inductor increases to maintain output voltage during output short, then the output voltage level is maintained, but the inductor saturates and FET damage occurs

Engineering Contradiction:

Improveoutput voltage maintenanceVSAvoidinductor saturation and FET damage

Core Design Contradiction:

PowerVSObject-affected harmful factors

Solution Approach 1:

The protection circuit takes preliminary action by continuously monitoring the current through the FET and comparing it against the temperature-adjusted threshold. When an overcurrent condition is detected before it causes inductor saturation or FET damage, the circuit immediately responds by shutting down the FET, preventing the harmful effects from occurring.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The patent implements a feedback mechanism where the actual current through the FET is continuously sensed and compared with the dynamic threshold. This feedback loop enables real-time detection and response to overcurrent conditions, allowing the system to maintain output voltage under normal conditions while preventing damage during fault conditions.

Inventive Principle:

Principle #23Feedback

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 damage to FET switches by accurately varying the overcurrent threshold with temperature, ensuring reliable operation of switch-mode power supplies across temperature changes.

Implementation Method 1

an on-resistance that varies based on a temperature coefficient of the switch

Methodology Applied

Scientific EffectTemperature coefficient: Thermal Expansion

Data Source

PatentUS11664648B2Programmable overcurrent protection for a switch

Publication Date: 2023.05.30 SILANNA ASIA

AI summary

Embodiments of the disclosure include a switch having an on-state resistance that varies based on a temperature coefficient of the switch and an overcurrent protection circuit coupled to the switch and having an adjustable overcurrent threshold level determined based on an adjustable voltage generated by the overcurrent protection circuit, the adjustable voltage generated based on the temperature coefficient of the switch.