Flyback Converter Controller Preventing Switch Overlap

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional flyback converters face issues with short-circuited current due to overlapping ON periods of primary and secondary side switches, especially when load conditions vary, which can damage the converters.

Innovation Solution

A switching controller circuit that generates adaptive switching signals based on resonance waveform characteristics to prevent simultaneous conduction of primary and secondary side switches, using a primary side control circuit and secondary side control circuit to synchronize switching times and adjust timing according to load changes, ensuring zero voltage switching without overlap.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If synchronous rectification is implemented on the secondary side to achieve zero voltage switching, then power conversion efficiency is improved, but the risk of overlapping ON periods between primary and secondary side switches increases, causing short-circuited current

Engineering Contradiction:

Improvepower conversion efficiencyVSAvoidshort-circuit protection

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent applies preliminary action by detecting the resonance waveform characteristics in advance and using them to predict when the secondary side switch should be turned off. The controller monitors the resonance waveform and generates the secondary side switching signal based on predicted timing, preventing overlapping conduction before it can occur. This is evident in the embodiment where the resonance waveform detection circuit detects the resonance waveform and the controller uses this information to control the secondary side switch timing.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback by continuously monitoring the resonance waveform characteristics and adjusting the secondary side switching timing accordingly. The resonance waveform detection provides real-time feedback to the controller, which adjusts the switching signal to maintain proper timing and prevent short-circuits. This feedback mechanism ensures that the secondary side switch is turned off before the primary side switch turns on, even under varying load conditions.

Inventive Principle:

Principle #23Feedback

2Device complexity

If fixed timing control is used for switching signals, then circuit complexity is reduced, but the switching timing cannot adapt to load changes, causing overlapping ON periods and short-circuited current

Engineering Contradiction:

Improvecontrol circuit complexityVSAvoidload adaptation capability

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent applies self-service by enabling the system to automatically detect resonance waveform characteristics and adjust its own switching timing without external intervention. The resonance waveform detection circuit and controller work together to self-regulate the switching timing based on actual operating conditions, eliminating the need for complex external control mechanisms while maintaining adaptability to load changes.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent implements parameter changes by dynamically adjusting the switching timing parameters based on detected resonance waveform characteristics. Instead of using fixed timing, the system modifies the switching signal timing parameters in response to changes in the resonance waveform, which vary with load conditions. This allows the system to adapt to different loads while maintaining simple circuit architecture.

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If the secondary side switch ON period is extended to improve rectification efficiency, then power conversion efficiency increases, but the likelihood of overlapping with primary side switch ON period increases, causing short-circuited current

Engineering Contradiction:

Improverectification efficiencyVSAvoidshort-circuited current

Core Design Contradiction:

Loss of energyVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary action by using resonance waveform detection to determine the optimal timing for turning off the secondary side switch before the primary side switch turns on. The system predicts the appropriate cutoff point based on the resonance waveform characteristics, ensuring that the secondary side switch is turned off in advance to prevent overlapping conduction, even when the ON period is extended for improved rectification efficiency.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS11496063B2Flyback converter and switching controller circuit and control method thereof

Publication Date: 2022.11.08 RICHTEK TECH

AI summary

A flyback converter includes a power transformer, a primary side switch, a secondary side switch and a controller. A secondary side switching signal has an SR pulse for achieving synchronous rectification, and a ZVS pulse for achieving zero voltage switching. The ZVS pulse is enabled according to a first characteristic of a resonance waveform, whereas, a primary side switching signal is enabled according to a second characteristic of resonance waveform. When an output current increases, the primary side switching signal is disabled during an inhibition interval, such that primary side switching signal does not overlap with the ZVS pulse, thereby preventing the primary and secondary side switches from being both conductive simultaneously. The inhibition interval is correlated with a rising edge of the primary side switching signal in a previous switching period and a resonance period of the resonance waveform.