Flyback Converter ZVS Control via Ringing Signal Detection

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Solution Overview

Problem

Prior art flyback power converters face challenges in precise synchronization of synchronous rectifier switches with primary side switches and low power conversion efficiency due to lack of zero voltage switching, leading to increased electromagnetic interference.

Innovation Solution

A zero voltage switching (ZVS) control circuit for flyback power converters that synchronizes the synchronous rectifier switch with the primary side switch using a ringing signal, achieving zero voltage switching by determining the trigger timing of the ZVS pulse based on the waveform characteristic of the ringing signal and incorporating jitter control to reduce electromagnetic interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If synchronous rectifier switch is controlled without precise synchronization with primary side switch, then device complexity is reduced, but power conversion efficiency deteriorates and electromagnetic interference increases

Engineering Contradiction:

Improvecontrol circuit complexityVSAvoidpower conversion efficiency

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The patent employs feedback mechanisms where the controller circuit monitors the operational state of the synchronous rectifier switch and adjusts the control signal timing accordingly. This feedback loop ensures precise synchronization between the synchronous rectifier switch and primary side switch, optimizing power conversion efficiency without significantly increasing system complexity.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The controller circuit automatically determines the trigger timing of the ZVS pulse based on waveform characteristics of ringing signals without requiring external intervention or complex synchronization circuits. This self-service approach achieves precise synchronization while keeping the control circuit relatively simple.

Inventive Principle:

Principle #25Self-service

2Device complexity

If primary side switch operates without zero voltage switching, then device complexity is reduced, but power conversion efficiency deteriorates

Engineering Contradiction:

Improveswitching control complexityVSAvoidpower conversion efficiency

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The patent implements preliminary action by generating a ZVS pulse that activates the synchronous rectifier switch before the main switching event occurs. This preliminary action ensures that the primary side switch operates under zero voltage switching conditions, improving power conversion efficiency. The ZVS pulse is determined based on waveform characteristics of ringing signals, maintaining relatively simple control logic.

Inventive Principle:

Principle #10Preliminary action

3Loss of energy

If synchronous rectifier switch is precisely synchronized with primary side switch using ringing signal, then power conversion efficiency is improved, but device complexity increases

Engineering Contradiction:

Improvepower conversion efficiencyVSAvoidcontrol circuit complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent replaces complex mechanical or hardware-based synchronization mechanisms with signal processing of ringing waveforms. By analyzing the waveform characteristics of naturally occurring ringing signals, the system achieves precise timing synchronization without requiring additional complex circuitry.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Device complexity

If ZVS pulse timing is fixed without jitter control, then device complexity is reduced, but electromagnetic interference increases

Engineering Contradiction:

Improvecontrol circuit complexityVSAvoidelectromagnetic interference

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The patent introduces periodic variations (jitter) to the ZVS pulse timing rather than maintaining a fixed periodic schedule. This periodic action with controlled randomness spreads out the electromagnetic interference spectrum, reducing peak EMI levels. The jitter is applied in a controlled manner that maintains overall system functionality while mitigating EMI issues.

Inventive Principle:

Principle #19Periodic action

Data Source

PatentUS10715028B2Flyback power converter and ZVS control circuit and control method thereof

Publication Date: 2020.07.14 RICHTEK TECH

AI summary

A ZVS (zero voltage switching) control circuit for controlling a flyback power converter includes: a primary side controller circuit for generating a switching signal, to control a primary side switch; and a secondary side controller circuit for generating a synchronous rectifier (SR) control signal for controlling a synchronous rectifier switch. The SR control signal includes an SR-control pulse and a ZVS pulse. The SR-control pulse controls the synchronous rectifier switch to perform secondary side synchronous rectification. The secondary side controller circuit determines a trigger timing point of the ZVS pulse according to a waveform characteristic of a ringing signal, to control the synchronous rectifier switch to be ON for a predetermined period, thereby achieving zero voltage switching of the primary side switch. The primary side or the secondary side controller circuit includes a jitter controller for performing jitter control on the ZVS pulse.