Inrush Current Limiter Circuit for DC-DC Power Converters

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Electronic devices experience damaging large inrush currents when initially powered, exceeding the current ratings of sensitive components, and existing inrush current limiting circuits may not adequately protect these components.

Innovation Solution

A DC-DC power converter with an inrush current limiter circuit that includes a resistor and a switch in parallel, controlled by a transistor, which bypasses the resistor when the voltage across it drops below a specified threshold, allowing safe current flow and protecting the switch from excessive inrush currents.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a resistor is used to limit inrush current, then sensitive components are protected from excessive current, but the resistor causes voltage drop and power loss during normal operation

Engineering Contradiction:

Improvecomponent protectionVSAvoidpower loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The circuit dynamically switches between two operational states: during power-on, the resistor is connected to limit inrush current; during normal operation, the resistor is bypassed to eliminate power loss. This dynamic reconfiguration resolves the contradiction by having the resistor serve its protective function only when needed.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The resistor is pre-positioned in the circuit path before power-on to automatically limit inrush current. The bypass switch is pre-configured to activate once the inrush phase completes, ensuring the resistor's protective function is available immediately when needed while preventing unnecessary power loss during normal operation.

Inventive Principle:

Principle #10Preliminary action

2Loss of energy

If a bypass switch is added to eliminate resistor power loss, then energy efficiency improves, but the circuit complexity increases

Engineering Contradiction:

Improvepower lossVSAvoidcircuit complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The circuit uses its own operational parameters (voltage across the resistor) to automatically control the bypass switch. When the voltage drop across the resistor exceeds a threshold indicating inrush current conditions, the switch activates to bypass the resistor, eliminating power loss without requiring external control logic.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The bypass switch is controlled by feedback from the voltage across the resistor. This feedback mechanism automatically detects inrush current conditions and activates the bypass accordingly, resolving the contradiction by using simple voltage-threshold detection rather than complex control logic.

Inventive Principle:

Principle #23Feedback

3Loss of energy

If the bypass switch remains closed during inrush, then power loss is reduced, but the switch and downstream components are damaged by excessive current

Engineering Contradiction:

Improvepower lossVSAvoidexcessive current damage

Core Design Contradiction:

Loss of energyVSObject-affected harmful factors

Solution Approach 1:

The resistor serves as an intermediary protective element during the inrush phase, limiting current before it reaches the switch and downstream components. The bypass switch acts as a second intermediary that, once activated, replaces the resistor's current-limiting function with a low-impedance path, eliminating power loss while maintaining protection during the critical inrush period.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

Effectively limits inrush currents by conducting them through a resistor during initial power-up, preventing damage to the switch and ensuring safe operation once the current drops below the threshold, thereby protecting the electronic device.

Implementation Method 1

The transistor is coupled to open the switch when the voltage across the resistor is above a specified inrush threshold to permit current flow through the resistor, and to close the switch when the voltage across the resistor is below the specified inrush threshold

Methodology Applied

Scientific EffectVoltage threshold detection: Ohm's Law

Implementation Method 2

a resistor coupled in an input current path to receive an inrush current from the input when the input is electrically coupled to the power source

Methodology Applied

Scientific EffectElectrical resistance: Electrical Resistance

Data Source

PatentUS11114844B2Inrush current limiter circuits and methods of limiting inrush current in a circuit

Publication Date: 2021.09.07 VERTIV CORP

AI summary

A DC-DC power converter includes an input, an output, a power circuit coupled between the input and the output to convert a voltage of a DC power received at the input to a different voltage of a DC power supplied at the output, and a control circuit. The DC-DC power converter also includes a resistor coupled in an input current path to receive an inrush current from the input, a switch coupled in parallel with the resistor to selectively bypass the resistor, and a transistor coupled to control the switch in response to a voltage across the resistor. The transistor is coupled to open the switch when the voltage across the resistor is above a specified inrush threshold to permit current flow through the resistor, and to close the switch when the voltage across the resistor is below the specified inrush threshold to bypass the resistor.