Single Stage Isolated PFC Converter With Active Clamp
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Solution Overview
Problem
Existing single stage isolated power factor corrected (PFC) converters face challenges in achieving high power operation with Zero Voltage Switching (ZVS) while minimizing electromagnetic interference (EMI) and input current Total Harmonic Distortion (THD), and require additional circuits for inrush current limiting and control complexity.
Innovation Solution
A single stage isolated PFC converter design featuring a full bridge rectifier, a power transformer with a resonant inductor, a damper circuit, an active clamp circuit, and a flipping circuit, which enables ZVS, reduces EMI, and achieves low input current THD without additional inrush current limiting circuits, using semiconductor switches and a control method that includes a comparator and logic circuitry for efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a full bridge rectifier followed by a boost converter and isolated DC/DC converter is used, then power factor correction and galvanic isolation are achieved, but device complexity and cost increase due to multiple conversion stages
Solution Approach 1:
The patent combines the PFC function and isolated DC/DC conversion into a single integrated converter stage. The circuit uses a full-bridge rectifier followed by a single isolated converter stage that performs both power factor correction and voltage conversion, eliminating the need for separate boost converter and isolated DC/DC converter stages. This merging reduces component count, simplifies control, and lowers cost while maintaining effective PFC and galvanic isolation.
2Reliability
If a boost converter stage is used for PFC, then input current waveform control is achieved, but inrush current requires additional limiting circuits
Solution Approach 1:
The patent employs a controlled rectifier bridge with thyristors or TRIACs that automatically limit inrush current through phase-angle control. The firing angle control inherently restricts the current waveform during startup and transient conditions, eliminating the need for separate inrush current limiting circuits. The same control mechanism that shapes the input current waveform for PFC also provides built-in inrush protection.
3Device complexity
If single stage PFC isolated converters using Flyback or SEPIC topologies are used, then device complexity is reduced, but they are suitable only for lower output powers and require additional circuit modifications for low input current THD
Solution Approach 1:
The patent segments the single converter stage into two parallel full-bridge legs, each with independent switches and transformers. This segmentation allows the converter to handle higher power levels by distributing the power handling across multiple parallel paths, overcoming the power limitations of single-stage Flyback or SEPIC topologies. The parallel configuration maintains relatively simple device structure while enabling high power operation.
4Loss of energy
If high frequency operation is implemented to maximize conversion efficiency, then EMI generation is minimized, but additional measures are needed to control switching losses and voltage spikes
Solution Approach 1:
The patent uses periodic reset of the transformer cores through the full-bridge configuration, where alternate legs operate during alternate half-cycles. This periodic action allows the use of high-frequency switching while managing core saturation and voltage spikes through controlled bidirectional switching. The regular resetting pattern enables efficient high-frequency operation with manageable EMI through predictable switching patterns.
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
The solution achieves high efficiency, low input current THD, and simplified control, with demonstrated 99% power factor, 3.3% THD, and greater than 95% efficiency, suitable for high power applications like programmable AC power sources and high voltage battery chargers.
Implementation Method 1
A resonant inductance, which can be located in series with the primary or secondary or be the transformer leakage inductance, conducts and limits the discharge current through S1 and D2 when S1 is on. The resonant frequency of Lr and the series combination of Cp and Cs can be selected to be higher or lower than the switching frequency of the converter
Implementation Method 2
The transformer T provides galvanic isolation and voltage conversion depending upon its turns' ratio Ns/Np
Implementation Method 3
an active clamp, as invented by Bruce Carsten for the forward converter is described in 'High Power SMPS Require Intrinsic Reliability', PCI '81 proceedings, September 1981, Munich, Germany, consisting of auxiliary switch S2 and clamp capacitor Cclamp was included to clamp the turn off voltage of the main switch S1
Data Source
AI summary
Two versions of an isolated single stage converter AC/DC Power Factor Corrected (PFC) converter topology have been invented. One is with a full bridge rectifier at its input and the other is a True Bridgeless version. The two versions of the topology feature new configurations and circuitry including a simplified damper circuit and a clamp capacitor flipping circuit and control methods that allow them to realize improved single stage isolated power factor converters which are suitable for high power operation, features Zero Voltage Switching to maximize conversion efficiency and to minimize Electro-Magnetic Interference generation, does not need an additional circuit to limit the inrush current, achieves reasonably low input current Total Harmonic Distortion (THD), and is easy to control. The second version provides a true bridgeless single stage isolated power factor converter with even higher efficiency and lower input current THD.