Active Clamp Flyback Converter Mode Switching

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Solution Overview

Problem

Conventional active-clamp flyback power converters face efficiency issues when the load is light due to circulating currents and struggle with electromagnetic interference (EMI) and audible noise, with existing solutions like the UCC28780 controller not fully utilizing the active-clamp circuit benefits.

Innovation Solution

The power converter employs a control method that adaptively switches between ACF and flyback modes based on load conditions, using current-sense signals and compensation signals to manage switching frequency and peak currents, eliminating the need for a bleeder resistor in the active-clamp circuit.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If active-clamp topology is used to improve power efficiency, then power efficiency is improved under heavy load, but power efficiency deteriorates under light load due to circulating currents

Engineering Contradiction:

Improvepower efficiencyVSAvoidload adaptability

Core Design Contradiction:

Loss of energyVSAdaptability or versatility

Solution Approach 1:

The patent implements dynamic operation mode switching between ACF mode and flyback mode based on real-time detection of output current magnitude. The controller adapts the operating mode to match load conditions, enabling the system to maintain high efficiency across both heavy and light load scenarios by selecting the optimal mode for each condition

Inventive Principle:

Principle #15Dynamics

2Use of energy by stationary object

If bleeder resistor is connected in parallel with capacitor to release accumulated energy, then energy release function is achieved, but power efficiency deteriorates due to continuous energy consumption

Engineering Contradiction:

Improveenergy release functionVSAvoidpower efficiency

Core Design Contradiction:

Use of energy by stationary objectVSLoss of energy

Solution Approach 1:

The patent removes the bleeder resistor from the active-clamp circuit entirely. Instead of continuously dissipating energy through resistance, the design allows the capacitor to retain energy and be utilized productively during subsequent switching cycles, eliminating the parasitic energy loss while maintaining the necessary energy release function through controlled discharge during normal operation

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent converts the previously harmful circulating current and accumulated energy (which required the bleeder resistor to dissipate) into a beneficial resource. The energy stored in the capacitor during off-states is now recovered and reused to support the next switching cycle, transforming what was waste energy into useful energy that improves overall system efficiency

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Power

If conventional ACF topology is used, then power conversion capability is achieved, but EMI and audible noise difficulties arise

Engineering Contradiction:

Improvepower conversion capabilityVSAvoidEMI and audible noise

Core Design Contradiction:

PowerVSObject-affected harmful factors

Solution Approach 1:

The patent implements periodic burst-mode operation where the converter operates in active-clamp flyback mode for a predetermined number of switching cycles, then enters a sleep mode with reduced switching activity. This periodic on-off pattern reduces the frequency and duration of EMI-generating switching events while maintaining adequate power conversion capability through accumulated energy transfer during active periods

Inventive Principle:

Principle #19Periodic action

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 enhances power conversion efficiency across varying loads, reduces EMI, and eliminates the need for a bleeder resistor, improving manufacturing efficiency and cost-effectiveness.

Implementation Method 1

Transformer TF includes primary winding LP, secondary winding LS and auxiliary winding LA, inductively coupled to each other

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

Secondary winding LS is connected to two opposite-polarity Schottky diodes D1 and D2, an output capacitor COUT and a load 13

Methodology Applied

Scientific EffectRectification: Diode

Data Source

PatentUS10666153B2Active clamp flyback converters and control methods thereof

Publication Date: 2020.05.26 LEADTREND TECH

AI summary

A control method for a power convert is disclosed. The power convert uses an active-clamp flyback topology and has low-side and high-side switches. The low-side switch is switched to generate consecutive switching cycles including a modified flyback cycle and a normal flyback cycle. Each of the consecutive switching cycles is not less than a blanking time generated in response to a load of the power converter. The high-side switch is constantly turned OFF during the normal flyback cycle. The high-side switch is turned ON after the blanking time during the modified flyback cycle to perform zero-voltage switching for the low-side switch.