Load Switch Soft Start Circuit for Inrush Current Control

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Solution Overview

Problem

Load switches generate high inrush currents when turned on, requiring large current capacity components and increasing power consumption and costs.

Innovation Solution

A control circuit with a controller that gradually increases the turn-on signal to the load switch through a GPIO port, using a soft start operation by repeatedly turning a switch on and off at a frequency range of 50 KHz to 400 KHz, to restrict the inrush current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If the load switch is turned on directly, then the turn-on response is fast, but a large inrush current is generated

Engineering Contradiction:

Improveturn-on response speedVSAvoidinrush current

Core Design Contradiction:

SpeedVSObject-generated harmful factors

Solution Approach 1:

The patent applies periodic action by repeatedly turning the switch on and off at a frequency range of 50 KHz to 400 KHz. This high-frequency switching creates a soft start operation that gradually charges the output capacitor, limiting inrush current while maintaining fast effective turn-on response. The periodic switching action transforms the harmful instantaneous inrush current into controlled incremental current flow.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent implements preliminary action by performing a soft start operation before the load switch fully turns on. The controller gradually increases the turn-on signal through repeated switching, preparing the circuit by incrementally charging the output capacitor. This preliminary gradual charging prevents the sudden large current surge that would occur with direct turn-on.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If the current capacity of the load switch component is increased to handle inrush current, then the inrush current can be managed, but the cost and device size increase

Engineering Contradiction:

Improveinrush current handling capabilityVSAvoidcomponent capacity specification

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent converts the harmful inrush current into a beneficial controlled charging process. By using high-frequency periodic switching, the原本的 harmful instantaneous current is transformed into a series of small incremental current pulses that safely charge the output capacitor. This allows the use of smaller capacity components while still achieving reliable inrush current management.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the temporal parameters of the turn-on signal by introducing high-frequency periodic switching (50 KHz to 400 KHz). This parameter change transforms the single large current event into multiple small current pulses over time, allowing smaller capacity components to handle the distributed current load effectively.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9791916B2Control circuit including load switch, electronic apparatus including the load switch, and control method thereof

Publication Date: 2017.10.17 SAMSUNG ELECTRONICS CO LTD

AI summary

A control circuit is provided. The control circuit includes a load switch, and a controller configured to transfer a turn-on signal which is increased step by step to the load switch, and perform a soft start operation which turns on the load switch. In response to the load switch being turned on, the control circuit restricts an inrush current flowing in the load switch.