Switching Converter Soft Stop Circuit for Overvoltage Protection

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Solution Overview

Problem

Switching converters, particularly in active clamp forward and flyback topologies, face high stress on power FETs during power down due to overvoltage and oscillations, leading to potential damage and increased costs with existing solutions, and they also experience undesirable 'last gasp' restarts during soft stop operations.

Innovation Solution

Incorporating a detection circuit to compare power stage voltage to a line undervoltage threshold, an input load circuit to switchably discharge the input capacitor, and a timer circuit to control the duration of discharge, preventing 'last gasp' restarts without increasing circuit complexity or cost.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If switching converters operate during power down, then power FETs are protected from overvoltage and oscillations, but high stress and potential damage occur due to existing solutions

Engineering Contradiction:

Improvepower FET protectionVSAvoidovervoltage and oscillations stress

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary action by detecting undervoltage conditions before they cause harmful effects and initiating soft stop operations in advance. The detection circuit monitors the power stage voltage and triggers the soft stop sequence before overvoltage and oscillations can damage the power FETs, preventing harm before it occurs rather than reacting after damage begins.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements preliminary anti-action by applying a counteracting force against the harmful overvoltage and oscillations. The soft stop circuit actively opposes the rising voltage and oscillatory behavior by controlling the power stage to reduce duty cycle and prevent the build-up of damaging voltage levels, thereby neutralizing the harmful effects before they can cause damage.

Inventive Principle:

Principle #9Preliminary anti-action

2Reliability

If soft stop operation is implemented, then power FET stress is reduced, but last gasp restarts occur during power down

Engineering Contradiction:

Improvepower FET stress reductionVSAvoidlast gasp restarts

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent applies feedback by continuously monitoring the power stage voltage during soft stop operations and using this information to control the power stage behavior. The detection circuit provides real-time voltage information back to the control logic, which adjusts the soft stop sequence accordingly, preventing last gasp restarts by detecting when voltage conditions indicate an attempted restart and maintaining the stopped state.

Inventive Principle:

Principle #23Feedback

3Reliability

If detection circuit is added to prevent last gasp restarts, then converter reliability improves, but circuit complexity increases

Engineering Contradiction:

Improvelast gasp preventionVSAvoidcircuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies universality by designing the detection circuit to serve multiple functions simultaneously. The same detection circuit that monitors for undervoltage conditions to initiate soft stop also detects power down conditions to prevent last gasp restarts, and provides voltage information for controlling the soft stop sequence. This multi-functionality eliminates the need for separate dedicated circuits for each function, thereby improving reliability without proportionally increasing complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 'last gasp' operations while protecting power FETs and reducing converter costs by safely discharging the input capacitance, ensuring the voltage falls below the undervoltage threshold, thus preventing unnecessary restarts and maintaining efficiency.

Implementation Method 1

The detection circuit is configured to compare voltage at a power stage voltage input to a line undervoltage threshold voltage

Methodology Applied

Scientific EffectVoltage comparison:

Implementation Method 2

The input load circuit is configured to, responsive to the soft stop operation, switchably reduce a resistance from the power stage voltage input to a ground terminal

Methodology Applied

Scientific EffectCapacitor discharge: Capacitance

Implementation Method 3

The input load circuit is configured to switchably reduce a resistance from the power stage voltage input to a ground terminal

Methodology Applied

Scientific EffectResistive discharge: Electrical Resistance

Implementation Method 4

The timer circuit is configured to set a duration of reduced resistance from the power stage voltage input to the ground terminal

Methodology Applied

Scientific EffectTime control:

Data Source

PatentUS11522441B2Switching converter controller with soft stop

Publication Date: 2022.12.06 TEXAS INSTRUMENTS INC

AI summary

A switching converter controller includes a detection circuit, an input load circuit, and a timer circuit. The detection circuit is configured to compare voltage at a power stage voltage input to a line undervoltage threshold voltage to initiate a soft stop operation. The input load circuit is coupled to the power stage voltage input. The input load circuit is configured to, responsive to the soft stop operation, switchably reduce a resistance from the power stage voltage input to a ground terminal. The timer circuit is configured to set a duration of reduced resistance from the power stage voltage input to the ground terminal.