Ramp Generator Circuit for Inrush Current Protection

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Solution Overview

Problem

Electronic devices face damage from inrush currents during power-up due to malfunctioning or missing soft-start capacitors, leading to overcurrent events and potential permanent damage.

Innovation Solution

A method involving a ramp generator circuit that determines the status of the soft-start capacitor, generating a normal voltage ramp if it's connected properly and a safety ramp if not, to control the power transistor's turn-on and reduce inrush current spikes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a soft-start capacitor is used to control inrush current, then inrush current is reduced, but the device becomes vulnerable to damage if the capacitor malfunctions or is absent

Engineering Contradiction:

Improveinrush currentVSAvoiddevice robustness

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The ramp generator circuit monitors the voltage at its input node and uses this feedback to determine whether to generate a normal or safety ramp. When the soft-start capacitor is absent or malfunctioning, the circuit detects the abnormal voltage condition and automatically switches to safety mode, generating a slower ramp to prevent inrush current damage.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The circuit prepares two different ramp generation modes in advance: normal mode with faster ramp when capacitor is present, and safety mode with slower ramp when capacitor is absent. By detecting the capacitor status before power-up and pre-selecting the appropriate ramp mode, the circuit provides beforehand protection against inrush current regardless of capacitor functionality.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

2Productivity

If the ramp generator always generates a normal voltage ramp for fast power-up, then productivity is improved, but device damage occurs when soft-start capacitor is malfunctioning

Engineering Contradiction:

Improvepower-up speedVSAvoidovercurrent damage

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The ramp generator dynamically adjusts its operation based on real-time detection of soft-start capacitor status. The circuit can switch between two operational states: generating normal voltage ramps for fast power-up when capacitor is functional, and generating safety ramps with slower rise time when capacitor is absent or malfunctioning. This dynamic adaptation optimizes both productivity and protection.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The circuit changes the voltage ramp parameters (slope, rise time) based on the detected capacitor condition. When capacitor is present, the ramp generator uses parameters that enable fast power-up. When capacitor is absent, the circuit automatically changes to different parameters that produce a slower, safer ramp to prevent inrush current damage.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If the circuit uses a safety ramp with smaller current, then device protection is improved, but power-up time increases

Engineering Contradiction:

Improveovercurrent protectionVSAvoidpower-up time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The circuit performs preliminary detection of the soft-start capacitor status before initiating the power-up sequence. By detecting whether the capacitor is present and functional in advance, the circuit can pre-select the appropriate ramp generation mode. This eliminates the need to use the conservative safety ramp when the capacitor is actually present, thus avoiding unnecessary power-up time delay while maintaining protection when needed.

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

This approach provides over-current protection and safe power-up even when soft-start capacitors malfunction or are absent, reducing the risk of damage by managing inrush currents effectively.

Implementation Method 1

a soft-start capacitor is electrically connected to an input of a ramp generator circuit

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

a first current is injected into the input of the ramp generator circuit to generate a first voltage ramp at the output of the ramp generator circuit

Methodology Applied

Scientific EffectElectrical current flow: Conduction (electrical)

Data Source

PatentUS11264893B2Method, circuit, and apparatus to increase robustness to inrush current in power switch devices

Publication Date: 2022.03.01 STMICROELECTRONICS SRL

AI summary

In accordance with an embodiment, a method includes receiving an enable signal. After the enable signal is asserted, it is determined whether a soft-start capacitor is electrically connected to an input of a ramp generator circuit while keeping an output of the ramp generator circuit low. If the soft-start capacitor is electrically connected to the input of the ramp generator circuit, a first current is injected into the input of the ramp generator circuit to generate a first voltage ramp at the output of the ramp generator circuit. If the soft-start capacitor is not electrically connected to the input of the ramp generator circuit, a second current is injected to the input of the ramp generator circuit to generate a second voltage ramp at the output of the ramp generator circuit. The second current is smaller than the first current.