Dynamic Gate Discharge for Short Circuit Protection

Solution Overview

Problem

Existing short circuit protection techniques for power switches, such as desaturation and collector current monitoring, are inefficient in quickly mitigating high current events, leading to excessive heat and energy loss due to prolonged protection times and potential overvoltage breakdown.

Innovation Solution

A gate driver circuit that discharges the gate of a switch through a pair of resistors with different resistances, switching from a low resistance to a high resistance when the voltage across parasitic inductance becomes zero, allowing for a controlled and rapid reduction in gate-to-emitter voltage and current, thereby protecting the switch from excessive heat and energy loss.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If desaturation or collector current monitoring is used for short circuit protection, then the switch is protected from high current, but the protection time is prolonged causing excessive heat and energy loss

Engineering Contradiction:

Improveshort circuit protectionVSAvoidheat and energy loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The gate discharge path is segmented into two separate resistors: a first resistor for initial rapid discharge and a second resistor for final discharge. This segmentation allows the system to use different discharge rates at different stages of the protection event, achieving both fast response and complete discharge while minimizing energy loss

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The gate discharge resistance is dynamically changed during the protection event. The system starts with a lower resistance for rapid current reduction, then transitions to a higher resistance for complete discharge. This dynamic adjustment optimizes both the speed of protection and the total energy dissipated

Inventive Principle:

Principle #15Dynamics

2Device complexity

If a single resistor is used for gate discharge, then the circuit is simple, but the rate of voltage reduction cannot be optimized to balance speed and voltage overshoot

Engineering Contradiction:

Improvecircuit complexityVSAvoidrate of voltage reduction

Core Design Contradiction:

Device complexityVSSpeed

Solution Approach 1:

The gate discharge resistance is dynamically changed during the protection event. The system starts with a lower resistance for rapid current reduction, then transitions to a higher resistance for complete discharge. This dynamic adjustment optimizes both the speed of protection and the total energy dissipated

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The resistance value is changed as a parameter during the discharge process. By switching between two different resistance values based on the voltage across the parasitic inductance, the system optimizes the discharge rate at different stages without requiring complex continuous adjustment mechanisms

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If rapid gate discharge is used to reduce protection time, then energy loss is minimized, but voltage overshoot may exceed safe operating regions

Engineering Contradiction:

Improveenergy lossVSAvoidvoltage overshoot

Core Design Contradiction:

Loss of energyVSObject-affected harmful factors

Solution Approach 1:

The gate discharge path is segmented into two separate resistors: a first resistor for initial rapid discharge and a second resistor for final discharge. This segmentation allows the system to use different discharge rates at different stages of the protection event, achieving both fast response and complete discharge while minimizing energy loss

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The second resistor with higher resistance value is prepared in advance as a cushioning element. When the voltage across the parasitic inductance reaches zero, this resistor is switched in to prevent voltage overshoot and ringing, protecting the switch from harmful voltage spikes while completing the discharge process

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 solution effectively reduces the duration of short circuit protection, minimizing heat and energy loss while maintaining peak voltage within safe operating limits, offering a more accurate and efficient method compared to existing techniques.

Implementation Method 1

The gate driver may include a comparator arranged to detect the voltage

Methodology Applied

Scientific EffectVoltage detection: Electric Field

Implementation Method 2

discharges a gate of the one through a first resistor, and responsive to a voltage across a parasitic inductance of the switch becoming zero, discharges the gate through a second resistor

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 3

protecting the switch from excessive heat and energy loss

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentUS11115019B2Dynamic short circuit protection

Publication Date: 2021.09.07 FORD GLOBAL TECH LLC

AI summary

Circuitry includes a pair of switches arranged in series, and a gate driver. The gate driver, responsive to a magnitude of current through one of the switches exceeding a threshold, discharges a gate of the one through a first resistor. The gate driver also, responsive to a voltage across a parasitic inductance of the switch becoming zero, discharges the gate through a second resistor but not the first resistor.