Capacitive Power Supply Inrush Current Limiting
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Solution Overview
Problem
Capacitive power supplies face challenges in minimizing power dissipation due to inrush current limitations, which are often addressed with series resistances that increase power consumption and require robust voltage limiting facilities, while also needing to manage peak voltages and component variations.
Innovation Solution
A capacitive power supply design incorporating a DC-conducting series impedance with a resistance value of at least 0.2 times that of the first chain, allowing for reduced inrush current limitation and power dissipation, while maintaining accurate output voltage control through an output voltage limiting facility, and accommodating component variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a series resistance is used to limit inrush current, then inrush current is reduced to safe levels, but power dissipation increases
Solution Approach 1:
The patent employs a NTC thermistor as the inrush current limiting component, which dynamically changes its resistance based on temperature. At cold startup, the NTC presents high resistance to limit inrush current. As current flows through it, the NTC heats up and its resistance automatically decreases, reducing power dissipation during normal operation. This dynamic behavior resolves the contradiction between limiting inrush current and minimizing ongoing power loss.
Solution Approach 2:
The patent changes the resistance parameter of the inrush limiting component based on operating conditions. The NTC thermistor's resistance transitions from high (at low temperature) to low (at high temperature), allowing the system to adaptively adjust the inrush current limitation strength. This parameter change enables effective inrush current protection while minimizing continuous power dissipation.
2Reliability
If a higher inrush resistance is used to protect against peak voltages, then component reliability is improved, but power dissipation increases
Solution Approach 1:
The NTC thermistor provides dynamic resistance adjustment that protects components during voltage peaks and inrush conditions while minimizing continuous power loss. The high initial resistance protects against inrush current and voltage spikes, then automatically reduces to maintain component protection with minimal power dissipation during steady-state operation.
Solution Approach 2:
The NTC thermistor is self-regulating, using the current flowing through it to heat itself and automatically adjust its resistance. This self-service mechanism provides over-current and over-voltage protection without external control, while the automatic resistance reduction minimizes power dissipation after the initial protection phase.
3Reliability
If a robust voltage limiting facility is designed to handle high inrush currents, then component protection is ensured, but device complexity and cost increase
Solution Approach 1:
The patent extracts the voltage limiting function from a complex active circuit and implements it through the passive NTC thermistor's inherent characteristics. The NTC's temperature-dependent resistance naturally limits voltage and current without requiring additional active components, control circuits, or complex logic, thereby simplifying the overall design while maintaining protection capabilities.
Solution Approach 2:
The NTC thermistor is a simple, inexpensive passive component that provides robust voltage and current limiting functionality. By using this low-cost component instead of complex active voltage limiting circuits, the patent achieves reliable component protection while minimizing device complexity and cost.
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 design significantly reduces power dissipation and allows for a lower inrush resistance without risking peak voltage issues, facilitating mass production and ensuring component reliability.
Implementation Method 1
In a capacitive power supply a capacitance functions as an impedance that causes a voltage drop from the main supply voltage to a voltage to be used by the application
Implementation Method 2
As a negative side effect however this series resistance dissipates power
Data Source
Figure 1
Figure 2~4
Figure 5
AI summary
A capacitive power supply comprises an input section (10) having input terminals(Ln, Nt) for connection to an AC- mains supply,and a capacitive coupling, a rectification section (20) coupled via the capacitive coupling to the input terminals (Ln, Nt),and an output section (30) coupled to the rectification section, the output section comprising -output terminals(V+, V-), for providing an output voltage to a load, -a first chain comprising a charge storage facility (C2), and -a second chain arranged in parallel to the first chain, and comprising an output voltage limiting facility (D5), the capacitive power supply further comprising an inrush current limiting facility (R1), wherein the output terminals (V+, V-)are connected to respective terminals of the output voltage limiting facility (D5), and the DC-conducting series impedance (Zdc) hasa resistive component witha resistive value of at least 0.2 times a resistive value of the first chain.