Soft Start Circuit for Regulator IC Voltage Overshoot

Solution Overview

Problem

Conventional series regulators fail to sufficiently suppress overshoot in output voltage during power-on, especially when the power supply voltage rises slowly, which can lead to device damage.

Innovation Solution

A semiconductor integrated circuit (regulator IC) with an output transistor, a control circuit, and a soft start circuit that gradually changes the voltage applied to the operation control transistor, delaying the activation of the control circuit during power-on, thereby reducing the rush current and overshoot.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional regulator circuit is used, then the circuit structure is simple, but the output voltage overshoot cannot be suppressed sufficiently during power-on

Engineering Contradiction:

Improveoutput voltage stabilityVSAvoidcircuit structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The soft start circuit performs preliminary action by gradually activating the error amplifier before full power-on operation. The circuit uses capacitors to slowly charge and activate the error amplifier in stages, preventing sudden rush current and output voltage overshoot before the main power stabilization begins.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The soft start circuit applies preliminary anti-action by preemptively controlling the error amplifier activation to counteract the potential rush current and overshoot. The circuit anticipates the power-on transient effects and applies opposing control through gradual error amplifier activation to prevent the harmful overshoot before it occurs.

Inventive Principle:

Principle #9Preliminary anti-action

2Speed

If the error amplifier is activated immediately at power-on, then the response property is improved, but output voltage overshoot occurs

Engineering Contradiction:

Improveresponse propertyVSAvoidoutput voltage overshoot

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The soft start circuit performs preliminary action by gradually activating the error amplifier before full power-on operation. The circuit uses capacitors to slowly charge and activate the error amplifier in stages, preventing sudden rush current and output voltage overshoot before the main power stabilization begins.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The soft start circuit introduces dynamic control by varying the error amplifier activation speed. The circuit transitions from gradual activation through capacitor charging to full activation, dynamically adjusting the error amplifier's operational state to balance response speed with overshoot prevention.

Inventive Principle:

Principle #15Dynamics

3Reliability

If a soft start circuit is added to suppress overshoot, then output voltage stability is improved, but device complexity increases

Engineering Contradiction:

Improveoutput voltage stabilityVSAvoidcircuit structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The soft start circuit performs preliminary action by gradually activating the error amplifier before full power-on operation. The circuit uses capacitors to slowly charge and activate the error amplifier in stages, preventing sudden rush current and output voltage overshoot before the main power stabilization begins.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The soft start circuit acts as an intermediary between the power input and the error amplifier. The capacitors in the soft start circuit serve as mediator elements that gradually transfer and control the power activation signal, smoothing the transition and preventing direct sudden activation of the error amplifier.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS11695338B2Semiconductor integrated circuit for a regulator for forming a low current consumption type DC power supply device

Publication Date: 2023.07.04 MITSUMI ELECTRIC CO LTD

AI summary

Disclosed is a semiconductor integrated circuit for a regulator for forming a low current consumption type DC power supply device. The semiconductor integrated circuit includes an output transistor, a control circuit, an operation control transistor and a soft start circuit. The output transistor is connected between an output terminal and a voltage input terminal to which a DC voltage is input. The control circuit controls the output transistor according to a feedback voltage of an output. The operation control transistor controls an operation state of the control circuit. The soft start circuit gradually changes a voltage applied to a control terminal of the operation control transistor and delays activation of the control circuit at a time of applying a power supply voltage to the voltage input terminal.