Power Factor Control Circuit Preventing Inrush Current
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Solution Overview
Problem
Existing power factor correction circuits suffer from reliability issues due to high inrush currents during startup, which can damage switches and increase energy losses, and require additional components to mitigate these issues, leading to higher costs.
Innovation Solution
A power factor control circuit with a switch and inductor series arrangement, where the output capacitor is connected between input nodes via the switch, and a rectifier is non-conductive when the switch is closed, preventing inrush currents and improving reliability by allowing energy storage in the inductor without immediate charging of the capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the output capacitor is directly connected to the mains input through the inductor and diode in known power factor control circuits, then the circuit can charge the capacitor, but a large inrush current occurs causing the inductor to reach saturation level and potentially damage the switch
Solution Approach 1:
The circuit performs preliminary action by establishing a controlled current path through the switch and inductor before allowing capacitor charging. The switch is driven to generate a substantially sinusoidal current that is synchronized with the mains voltage, preparing the inductor to store energy in a controlled manner before the rectifier becomes conductive and charges the output capacitor, thereby preventing inrush current
Solution Approach 2:
The switch acts as an intermediary element between the mains input and the output capacitor. By controlling the switch timing and using it to generate a sinusoidal current synchronized with the mains voltage, the circuit mediates the energy transfer process, allowing the inductor to store energy first and then transfer it to the capacitor through the rectifier, preventing direct inrush current
2Reliability
If the inductor reaches saturation level due to inrush current, then the current through the switch becomes unregulated, but this can damage the switch and reduce circuit reliability
Solution Approach 1:
The drive circuit provides feedback control by monitoring the current through the switch and adjusting the switch timing accordingly. The drive circuit is arranged for driving the switch to generate a substantially sinusoidal current that is substantially synchronized with the mains voltage, ensuring the current remains regulated and prevents inductor saturation that would lead to unregulated current and potential switch damage
3Reliability
If additional components are added to mitigate inrush current issues in known circuits, then reliability may improve, but the device complexity and cost increase
Solution Approach 1:
The switch serves multiple functions: it acts as a current regulator to generate sinusoidal current synchronized with mains voltage, serves as an energy storage element controller for the inductor, and controls the timing of energy transfer to the capacitor. This multi-functionality eliminates the need for separate inrush current limiting components, reducing circuit complexity while maintaining reliability
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 configuration effectively prevents inrush currents, enhances switch reliability, and allows for controlled sinusoidal current and voltage regulation, reducing the need for expensive components and energy losses, while maintaining cost-effectiveness.
Implementation Method 1
current flows into the inductor which causes energy to be stored in the inductor
Implementation Method 2
a series arrangement of a rectifier and an output capacitor arranged parallel to the inductor, the rectifier being non-conductive when the switch is closed
Data Source
AI summary
The invention relates to a power factor control circuit (10) and to a universal mains power supply (100). The power factor control circuit comprises input nodes (n1, n2) which receive a rectified input voltage being a rectified mains input voltage, and a drive circuit (IC1) which drives a switch (M1). A series arrangement of the switch and an inductor (L1) is arranged between the input nodes. A series arrangement of a rectifier (D1) and an output capacitor (C2) is arranged parallel to the inductor (L1). The rectifier is non-conductive when the switch is closed. The drive circuit drives the switch for generating a substantially sinusoidal current through the switch being substantially synchronized with a sinusoidal voltage of the mains input voltage. Due to the arrangement the output capacitor in the power factor control circuit according to the invention, the output capacitor can only be charged after a first conducting cycle of the switch. An effect of this arrangement is that no inrush current can occur until after the first conducting cycle of the switch which improves the reliability of the power factor control circuit according to the invention.