Flyback Converter Active Clamp Snubber Soft Switching Control

Solution Overview

Problem

Conventional flyback power converters face power loss due to misalignment between the primary side switch turn-on time and zero voltage switching, leading to undesirable circular resonance between the magnetic inductor and snubber capacitor, which reduces power conversion efficiency.

Innovation Solution

The flyback power converter adjusts the starting and ending times of the snubber switch's ON period within the soft switching period, ensuring the primary side switch achieves soft switching while controlling the secondary side current threshold, thereby reducing power loss and improving efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If the primary side switch and snubber switch switch in opposite phases with a constant dead time, then the circuit structure is simple and easy to control, but the primary side switch turn-on time may not align with zero voltage switching, causing circular resonance and power loss

Engineering Contradiction:

Improveswitching control simplicityVSAvoidpower loss

Core Design Contradiction:

Ease of operationVSLoss of energy

Solution Approach 1:

The patent applies dynamics by making the snubber switch control dynamic instead of fixed. The controller determines the snubber switch turn-on timing based on real-time detection of primary side current and voltage conditions, allowing the switching timing to adapt to varying operating conditions and achieve optimal zero voltage switching alignment

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent implements feedback by using the controller to detect primary side current and voltage conditions, then using this feedback information to determine the appropriate timing for turning on the snubber switch. This closed-loop control ensures the primary side switch turns on at the optimal zero voltage switching moment

Inventive Principle:

Principle #23Feedback

2Reliability

If the dead time between primary side switch and snubber switch is extended, then soft switching is achieved, but the switching period is lengthened reducing productivity

Engineering Contradiction:

Improvesoft switching achievementVSAvoidswitching frequency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent applies dynamics by making the snubber switch control dynamic instead of fixed. The controller determines the snubber switch turn-on timing based on real-time detection of primary side current and voltage conditions, allowing the switching timing to adapt to varying operating conditions and achieve optimal zero voltage switching alignment

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent implements feedback by using the controller to detect primary side current and voltage conditions, then using this feedback information to determine the appropriate timing for turning on the snubber switch. This closed-loop control ensures the primary side switch turns on at the optimal zero voltage switching moment

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

This approach reduces unwanted power loss and enhances power conversion efficiency by ensuring the primary side switch operates during optimal soft switching conditions, maintaining the secondary side current above a threshold and adapting the ending time based on the primary side switch voltage.

Implementation Method 1

the energy stored in the snubber capacitor can discharge a parasitic capacitor Coss of the primary side switch S1, so that the primary side switch S1 can achieve soft switching when the primary side switch S1 is turned ON

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

when the primary side switch S1 is turned OFF, the electrical energy stored in the primary winding W1 is transferred from the primary winding W1 to the secondary winding W2

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS11545909B2Flyback power converter and active clamp snubber thereof

Publication Date: 2023.01.03 RICHTEK TECH

AI summary

A flyback power converter includes: a power transformer, a primary side control circuit, a secondary side control circuit, and an active clamp snubber including a snubber switch and a control signal generation circuit. The control signal generation circuit controls the snubber switch to be conductive during a soft switching period in an OFF period of a primary side switch within a switching period of the switching signal, whereby the primary side switch achieves soft switching. A starting time point of the soft switching period is determined by a current threshold, so that a secondary side current is not lower than the current threshold at the starting time point, whereby the secondary side control circuit keeps the SR switch conductive at the starting time point. The secondary side control circuit turns OFF the SR switch when the secondary side current is lower than the current threshold.