Single-Stage PFC Converter Without Input Electrolytic Capacitor
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Solution Overview
Problem
Existing offline power converters suffer from poor power factor due to high capacitance input electrolytic capacitors, which cause distortion in input line current and lead to feedback loop instability, transformer saturation, and increased size and cost.
Innovation Solution
A single stage power factor correction (PFC) converter design that eliminates the need for an input electrolytic capacitor by using a transformer, power device, and switching controller with frequency compensation, achieving constant voltage and current output without an extra PFC power stage, utilizing high-speed diodes and a small filtering capacitor to improve reliability and reduce size and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a high capacitance input electrolytic capacitor is used, then the input voltage is maintained stable, but the power factor deteriorates and the input line current is distorted
Solution Approach 1:
The patent removes the high capacitance input electrolytic capacitor from the circuit entirely. Instead of using a capacitor to maintain input voltage, the design relies on the transformer and switching controller to regulate voltage, thereby eliminating the harmful current distortion and poor power factor caused by the capacitor while maintaining stable output voltage.
Solution Approach 2:
The patent implements a feedback control mechanism where the switching controller monitors the output voltage and adjusts the switching duty cycle accordingly. This feedback loop maintains stable output voltage without requiring a large input capacitor, thereby avoiding the current distortion and power factor issues associated with high capacitance input filters.
2Object-generated harmful factors
If the capacitance of the input electrolytic capacitor is reduced to improve power factor, then the power factor improves, but the input voltage becomes low causing feedback open loop
Solution Approach 1:
The patent eliminates the input electrolytic capacitor entirely, removing the need to balance capacitor size against power factor. The feedback loop stability is maintained through direct voltage sampling at the transformer primary side and appropriate compensation network design, allowing the system to achieve both high power factor and stable feedback operation.
Solution Approach 2:
The patent introduces a compensation capacitor connected to the switching controller as an intermediary element. This capacitor provides the necessary phase compensation for the feedback loop without being part of the input filter, thereby maintaining feedback stability while allowing the input stage to operate with high power factor and minimal distortion.
3Stability of the object's composition
If a high capacitance input electrolytic capacitor is used, then the input voltage is maintained, but the converter size, cost, and reliability deteriorate
Solution Approach 1:
The patent removes the large input electrolytic capacitor from the design, eliminating the reliability issues and size/cost penalties associated with high-capacitance electrolytic capacitors. The input voltage is maintained through the transformer's voltage transformation ratio and the switching controller's regulation, without requiring a large capacitor.
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 a high power factor with reduced size and cost, eliminating the need for an extra PFC stage, improving reliability, and preventing transformer saturation while maintaining stable output voltage and current.
Implementation Method 1
The capacitor is coupled to the switching controller to provide frequency compensation for a feedback loop of the power converter
Implementation Method 2
The transformer 10 includes a primary winding NP, an auxiliary winding NA, and a secondary winding NS
Data Source
AI summary
An exemplary embodiment of a power converter is provided. The power converter includes a transformer, a power device, a switching controller, and a capacitor. The power device is coupled to the transformer for switching the transformer to product output of the power converter. The switching controller receives a feedback signal for generating a switching signal coupled to drive the power device. An input circuit of the switching controller is coupled to the transformer to sample an input signal for generating the feedback signal, and the input signal is correlated to the output of the power converter. The capacitor is coupled to the switching controller to provide frequency compensation for a feedback loop of the power converter. Input of the power converter is without an electrolytic capacitor, and a maximum output current of the power converter is a constant current.