Inrush Current Limiter Using Charge Pump Bypass

Solution Overview

Problem

Existing inrush current limiters in power supplies suffer from high losses during normal operation and increased complexity, requiring large relays that are costly and consume excessive switching power, which negatively impacts manufacturing costs and circuit efficiency.

Innovation Solution

A semiconductor switch controlled by a charge pump circuit is used to bypass the inrush current limiter, eliminating the need for relays and incorporating NTC thermistors to limit inrush currents, resulting in reduced no-load energy losses and smaller, more cost-effective circuitry.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a relay is used to bypass the inrush current limiter during normal operation, then the inrush current limiting function is effective, but the device complexity, manufacturing cost, and open circuit losses increase significantly

Engineering Contradiction:

Improveinrush current limiting capabilityVSAvoidcircuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces the mechanical relay system with an electronic switching mechanism using a MOSFET transistor (Q1) controlled by a microcontroller (U1). This substitution eliminates the mechanical moving parts, contacts, and associated drive circuitry of the relay, thereby reducing device complexity while maintaining the bypass functionality. The MOSFET acts as an electronic switch that can be precisely controlled by the microcontroller to bypass the NTC thermistor during normal operation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If a relay is used to bypass the inrush current limiter, then inrush current limiting is achieved, but manufacturing cost and switching power consumption increase

Engineering Contradiction:

Improveinrush current limiting capabilityVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent replaces the mechanical relay system with an electronic switching mechanism using a MOSFET transistor (Q1) controlled by a microcontroller (U1). This substitution eliminates the mechanical moving parts, contacts, and associated drive circuitry of the relay, thereby reducing device complexity while maintaining the bypass functionality. The MOSFET acts as an electronic switch that can be precisely controlled by the microcontroller to bypass the NTC thermistor during normal operation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent uses inexpensive electronic components (MOSFET, microcontroller, resistors, capacitors) to replace the more expensive relay assembly. The MOSFET Q1 and associated control circuitry represent a more cost-effective solution compared to relay hardware, reducing manufacturing costs while achieving the same functional outcome of bypassing the inrush current limiter during steady-state operation.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Reliability

If a relay is used to bypass the inrush current limiter, then inrush current limiting is achieved, but audible noise and open circuit losses increase

Engineering Contradiction:

Improveinrush current limiting capabilityVSAvoidaudible noise

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent replaces the mechanical relay system with an electronic switching mechanism using a MOSFET transistor (Q1) controlled by a microcontroller (U1). This substitution eliminates the mechanical moving parts, contacts, and associated drive circuitry of the relay, thereby reducing device complexity while maintaining the bypass functionality. The MOSFET acts as an electronic switch that can be precisely controlled by the microcontroller to bypass the NTC thermistor during normal operation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Object-affected harmful factors

If resistive elements are used to limit inrush current, then inrush current is reduced, but power losses during normal operation increase

Engineering Contradiction:

Improveinrush currentVSAvoidpower loss during normal operation

Core Design Contradiction:

Object-affected harmful factorsVSLoss of energy

Solution Approach 1:

The patent implements a dynamic switching system that changes the circuit configuration based on operational state. During startup, the NTC thermistor (R1) is in the circuit to limit inrush current. During normal operation, the MOSFET Q1 is activated to bypass the NTC thermistor, dynamically transitioning from a high-resistance configuration to a low-resistance configuration. This dynamic adaptation eliminates continuous power losses in the resistive element while maintaining inrush current protection when needed.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent uses the NTC thermistor (R1) to preliminarily limit inrush current during the startup phase before normal operation begins. The thermistor is positioned in the circuit in advance to handle the transient inrush condition, and once the startup phase is complete, the bypass switch is activated to remove the thermistor from the current path, preventing continuous energy losses during steady-state operation.

Inventive Principle:

Principle #10Preliminary action

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 significantly reduces power consumption and manufacturing costs, eliminates audible noise, and minimizes open circuit losses, while maintaining effective inrush current limiting capabilities.

Implementation Method 1

NTC thermistors, for example, can be used to limit inrush current

Methodology Applied

Scientific EffectNegative temperature coefficient (NTC): Thermistor

Implementation Method 2

a charge pump circuit connected to a control terminal of the semiconductor switch for controlling the semiconductor switch

Methodology Applied

Scientific EffectCharge pump:

Data Source

PatentEP3618250B1Inrush current limiting device and power factor correction circuit

Publication Date: 2021.02.17 FRIWO GERAETEBAU GMBH

Figure 1~2
Figure 3

AI summary

The present invention relates to an inrush current limiting device and to a power factor correction circuit comprising an inrush current limiter. In particular, the present invention relates to a power factor correction circuit for controlling an inrush current limiter in a power conversion system used as a power supply. An inrush current limiting device (106) for limiting inrushing current to a connectable load (104) comprises a first node (110) and a second node (112), a resistive limiter unit (114, R3) for limiting current flowing through said limiter unit (114, R3) from said first to said second node, and a controllable bridging device (118) which is connected between said first and said second nodes (110, 112) in parallel to the limiter unit (114, R3), wherein the bridging device (118) comprises a semiconductor switch (T2) and a charge pump circuit (C1, D3, D4) connected to a control terminal of the semiconductor switch (T2) for controlling the semiconductor switch.