Flyback Converter Low Line Operation Extension

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Solution Overview

Problem

Flyback converters in audio amplifiers experience hard switching and potential semiconductor failure at low line voltages due to slow voltage transitions at the quasi-resonant pin of the controller IC, leading to system shutdowns.

Innovation Solution

Incorporating a transition component, such as a DC offset or resistor, between the quasi-resonant pin and the output pin of the controller IC to ensure the voltage exceeds a predefined threshold, facilitating fast and consistent pulse width modulation and preventing hard switching.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If quasi resonant flyback converter is used to improve efficiency, then energy efficiency is improved, but voltage transition time at QR pin increases causing hard switching

Engineering Contradiction:

Improveenergy efficiencyVSAvoidvoltage transition time

Core Design Contradiction:

Loss of energyVSSpeed

Solution Approach 1:

A resistor is introduced as an intermediary component between the QR pin and ground to form an RC circuit that accelerates the voltage transition at the QR pin. This intermediary element modifies the time constant of the circuit to ensure faster voltage rise time while maintaining the quasi-resonant operation benefits.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The circuit parameters are modified by adding a resistor to change the time constant (τ = RC) of the RC circuit at the QR pin. This parameter change accelerates the voltage transition from slow to fast, preventing hard switching while preserving the soft switching benefits for efficiency.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If voltage transition is slow at low line, then system can operate at lower voltages, but MOSFET turns on again causing hard switching and potential failure

Engineering Contradiction:

Improvelow line operation capabilityVSAvoidMOSFET switching reliability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The RC circuit is configured to preliminarily ensure the QR pin voltage reaches the required threshold level before the MOSFET turns on. This preliminary voltage establishment prevents the MOSFET from turning on again during the transition period, eliminating hard switching and potential failure modes.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The RC circuit provides a cushioning effect by maintaining the QR pin voltage above the threshold level for a sufficient duration, creating a time margin that prevents premature MOSFET turn-on. This beforehand cushioning protects against hard switching and potential component failure.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Speed

If DC offset is added to QR pin to ensure voltage threshold, then voltage transition speed is improved, but circuit complexity increases

Engineering Contradiction:

Improvevoltage transition speedVSAvoidcircuit complexity

Core Design Contradiction:

SpeedVSDevice complexity

Solution Approach 1:

A simple, inexpensive resistor is used instead of complex active circuits to achieve the voltage transition speed improvement. The resistor forms a passive RC circuit that provides the necessary function without adding significant complexity, making it a cost-effective and simple solution.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Data Source

PatentUS11522463B2System and method to extend low line operation of flyback converters

Publication Date: 2022.12.06 HARMAN PROFESSIONAL INC

AI summary

An amplifier system may include at least one input source, a flyback converter including a pair of complementary metal oxide silicon field effect transistor (MOSFETs), a controller integrated circuit (IC) having a quasi-resonant (QR) pin and configured to provide a biased drive current to the flyback converter, and a transition component arranged at the controller IC and configured to correct pulse width modulation at the IC to ensure the voltage at a transition pin of the IC is above a predefined threshold during a resonant transition.