Flyback AC-DC Converter Control for Dead-Time Loss Reduction
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Solution Overview
Problem
Flyback topology-based AC-DC adapters face inefficiencies due to discontinuous operation modes and large voltage range requirements, leading to size and efficiency challenges, especially in miniaturized portable equipment applications.
Innovation Solution
The proposed AC-DC converter circuit incorporates a control switch and a controlled current source activated during dead time, utilizing parasitic energy to enhance efficiency, and employs a bulk capacitor configuration with totem pole capacitors to optimize energy transfer and reduce power dissipation across the bridge rectifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If flyback topology is used to operate over large input voltage range (79Vdc to 375Vdc), then adaptability to universal AC voltage standards is improved, but efficiency deteriorates due to discontinuous operation mode and large voltage ratio
Solution Approach 1:
The patent implements dynamic operation mode switching between discontinuous conduction mode (DCM) and continuous conduction mode (CCM) based on input voltage levels. At low input voltages, the converter operates in DCM for optimal performance, while at high input voltages, it transitions to CCM. This dynamic adaptation resolves the contradiction by optimizing efficiency across the entire universal input voltage range while maintaining adaptability to all AC standards.
Solution Approach 2:
The patent changes key operating parameters including switching frequency, duty cycle, and conduction mode based on input voltage conditions. By dynamically adjusting these parameters, the converter maintains high efficiency across the 79Vdc to 375Vdc input range while preserving universal adaptability.
2Ease of operation
If discontinuous conduction mode is used in flyback topology, then simplicity of operation is improved, but efficiency deteriorates due to dead time and energy loss
Solution Approach 1:
The patent dynamically switches between discontinuous and continuous conduction modes based on operating conditions. While DCM offers simplicity, the system transitions to CCM at high voltages to eliminate dead time losses, thus resolving the contradiction between operational simplicity and efficiency.
Solution Approach 2:
By implementing continuous conduction mode operation at high input voltages, the patent eliminates the dead time period where no energy transfer occurs in discontinuous mode. This ensures continuous useful action and improves efficiency while maintaining the simplicity of the flyback topology through controlled continuity.
3Ease of manufacture
If conventional bridge rectifier configuration is used, then ease of manufacture is improved, but efficiency deteriorates due to high RMS current and power dissipation
Solution Approach 1:
The patent optimizes the bridge rectifier configuration by selecting appropriate diode types and arranging them in specific configurations that reduce RMS current. By changing the electrical parameters of the rectifier components and their arrangement, the system maintains ease of manufacture while significantly reducing power dissipation and improving efficiency.
Data Source
AI summary
A method of optimizing the efficiency of an AC-DC converter, wherein the energy extraction time from the AC line is increased and as result the size of the bulk capacitor can be decreased and in applications wherein the size of the bulk capacitor is maintained constant the ripple across the bulk capacitor is decreased. The methods presented also increase the power factor in AC-DC converters. Extending the energy extraction from the AC line also lowers the RMS current through the input bridge and the input bulk capacitor. The reduction of the ripple across the bulk capacitor also increases the efficiency of the DC-DC converter, increasing in this way the overall efficiency of the AC-DC converter.