Step-Down Converter Overvoltage Protection Circuit

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Solution Overview

Problem

Step down converters in automotive applications face critical failures due to high-side switch shorts, leading to overvoltage on the converter output, potentially damaging electronic components.

Innovation Solution

Incorporating a protection device, such as an n-channel metal-oxide-semiconductor field-effect transistor, in series with the switching circuit to limit output voltage by switching to a voltage-follower mode when the output voltage rises above a predetermined level, and using a control voltage to manage the protection device's operation, thereby preventing overvoltage damage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a protection device is added to limit output voltage, then reliability is improved, but device complexity increases

Engineering Contradiction:

Improveprotection against overvoltage damageVSAvoidcircuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The protection device acts as an intermediary element inserted in series between the switching circuit and the output. This mediator limits the output voltage by switching to voltage-follower mode when overvoltage occurs, thereby protecting the load without requiring complex control circuits or multiple protection components.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The protection device changes its operating parameter (switching mode) based on the output voltage level. When the output voltage exceeds a predetermined threshold, the device transitions from normal operation mode to voltage-follower mode, automatically adjusting its electrical characteristics to limit the voltage and prevent damage.

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If a protection device is added to limit output voltage, then object-affected harmful factors are reduced, but device complexity increases

Engineering Contradiction:

Improveovervoltage damage to load devicesVSAvoidconverter structure

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The protection device serves as a protective intermediary that intercepts and limits overvoltage before it can reach the load devices. By positioning this single protective element in series with the output, the patent eliminates the need for multiple protection circuits or complex surge suppression networks.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The protection device automatically detects and responds to overvoltage conditions without external intervention. When the output voltage rises above the predetermined level, the device self-activates by switching to voltage-follower mode, providing autonomous protection against harmful overvoltage effects.

Inventive Principle:

Principle #25Self-service

3Productivity

If efficiency is maximized, then productivity is improved, but reliability deteriorates due to vulnerability to switch shorts

Engineering Contradiction:

Improveconverter efficiencyVSAvoidsurvival under single point failure

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The protection device provides beforehand cushioning against the harmful effects of high-side switch shorts. By being pre-positioned in series with the output, it creates a safety buffer that automatically activates when a single point failure occurs, allowing the converter to continue operating in a degraded but safe mode rather than completely failing.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The protection device converts the harmful effect of a high-side switch short into a beneficial outcome. When a short occurs, the protection device detects the resulting overvoltage condition and switches to voltage-follower mode, which limits the output voltage to safe levels. This transforms a potentially catastrophic failure into a controlled, survivable event that maintains system functionality.

Inventive Principle:

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

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 limits the output voltage to prevent damage to load devices, ensuring they maintain functionality while reducing efficiency loss by less than 1% and protecting the protection device from damage.

Implementation Method 1

controlling an n-channel metal oxide semiconductor field effect transistor in a series circuit between a switching output of a step down converter and an output node of the step down converter to operate in triode mode; switching the n-channel transistor to operate in a voltage-follower mode wherein the n-channel transistor prevents an output voltage of the step down converter from being driven above a control voltage of the n-channel transistor minus a threshold voltage

Methodology Applied

Scientific EffectField-effect transistor operation:

Implementation Method 2

a protection device coupled in series between the second terminal of the inductor and the converter output and including a control terminal... an n-channel metal-oxide-semiconductor field-effect transistor

Methodology Applied

Scientific EffectSemiconductor field-effect transistor operation:

Data Source

PatentUS10277111B2Output overvoltage protection for converters

Publication Date: 2019.04.30 INFINEON TECHNOLOGIES AG

AI summary

According to an example, a step down converter includes switching circuit configured to control a switching output in order to generate an output voltage on a converter output within a specified range of a target voltage. The step down converter includes an inductor includes a first terminal and a second terminal, the first terminal coupled to the switching output, and a protection device coupled in series between the second terminal of the inductor and the converter output and including a control terminal. The protection device limits the output voltage supplied at the converter output based on a control voltage at the control terminal.