Power Transistor Gate Current Injection to Limit Voltage Overshoot

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Solution Overview

Problem

In power circuits, sudden current changes due to over-current conditions, such as short circuits, can lead to voltage overshoots caused by parasitic inductance, which existing gate drivers may address inadequately by switching off power transistors too quickly.

Innovation Solution

A system comprising a capacitive and resistive divider circuitry that injects current into the gate of a power transistor to prevent premature shutdown, using a capacitive divider to pass high and mid-frequency components of voltage transients and a resistive divider to bias the gate, thereby maintaining current flow and preventing voltage overshoots.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the gate driver switches off the power transistor quickly to protect against over-current conditions, then the reliability of the power circuit is improved, but voltage overshoot occurs due to parasitic inductance

Engineering Contradiction:

Improveprotection against over-current conditionsVSAvoidvoltage overshoot

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The circuit applies preliminary anti-action by detecting the voltage transient that precedes dangerous voltage overshoot and activating the transistor to inject gate current in advance, preventing the overshoot from occurring in the first place rather than reacting after it occurs

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The circuit converts the harmful voltage transient (which normally indicates impending overshoot) into a beneficial signal that triggers the protective mechanism. The parasitic inductance that causes overshoot is countered by using the same transient condition to activate current injection that maintains safe voltage levels

Inventive Principle:

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

2Reliability

If the power transistor is switched off completely to prevent damage, then the reliability is improved, but the productivity of the power circuit decreases due to premature shutdown

Engineering Contradiction:

Improveprotection against damageVSAvoidcurrent flow continuity

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

Instead of completely switching off the power transistor, the circuit applies partial action by injecting only the necessary amount of gate current required to maintain safe operation. This excessive gate current injection prevents complete shutdown while still providing adequate protection, allowing the transistor to remain in a controlled conducting state

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The circuit maintains continuity of useful action by keeping the power transistor in a controlled conducting state rather than completely shutting it off. The transistor continues to conduct current safely through the load while the protective mechanism ensures voltage remains within safe limits, avoiding premature shutdown

Inventive Principle:

Principle #20Continuity of useful action

3Speed

If existing gate drivers switch off the power transistor rapidly, then the response speed to over-current conditions is improved, but voltage overshoot exceeds safe levels

Engineering Contradiction:

Improveresponse speed to over-current conditionsVSAvoidvoltage overshoot magnitude

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The circuit employs feedback by continuously monitoring the voltage at the first terminal of the power transistor and using this information to control the transistor's gate current injection. The voltage transient detection and subsequent gate current adjustment form a closed-loop feedback system that maintains voltage within safe limits while responding rapidly to over-current conditions

Inventive Principle:

Principle #23Feedback

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 reduces voltage overshoots by maintaining power transistor conduction, limiting voltage drops to safe levels, as demonstrated by simulated performance showing a reduction from 800V to approximately 560V during short circuit conditions.

Implementation Method 1

a capacitive divider coupled to the first terminal of the power transistor and the gate of the transistor

Methodology Applied

Scientific EffectCapacitive coupling: Capacitance

Implementation Method 2

a resistive divider coupled to the first terminal of the power transistor and the gate of the transistor

Methodology Applied

Scientific EffectVoltage division: Electrical Resistance

Implementation Method 3

a transistor comprising a gate, a first terminal, and a second terminal coupled to the gate of the power transistor to inject current to the gate of the power transistor when the transistor is on

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS10756726B2Systems with power transistors, transistors coupled to the gates of the power transistors, and capacitive dividers coupled to the power transistors

Publication Date: 2020.08.25 TEXAS INSTRUMENTS INC

AI summary

An example system comprises: a power transistor comprising a gate, a first terminal, and a second terminal; a transistor comprising a gate, a first terminal, and a second terminal coupled to the gate of the power transistor; a capacitive divider coupled to the first terminal of the power transistor and the gate of the transistor; and a resistive divider coupled to the first terminal of the power transistor and the gate of the transistor.