Motor Driver Spike Suppression via RC Snubber Circuit

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Solution Overview

Problem

Motor driver circuits face challenges in suppressing spikes in the offset voltage due to increased gate drive inductance caused by mechanical restrictions that require MOSFETs to be separated from the driver, leading to spiking levels exceeding the driver's rating limits.

Innovation Solution

Incorporating a resistor-capacitor (RC) or ferrite bead-capacitor circuit between the high side MOSFET source pin and the junction of the high side and low side MOSFETs to filter driver spikes, allowing normal switching waveforms to pass through while attenuating ringing and undershoot.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If MOSFETs are separated from the driver due to thermal restrictions, then thermal management is improved, but gate drive inductance increases causing voltage spikes to exceed driver ratings

Engineering Contradiction:

Improvethermal managementVSAvoidvoltage spike

Core Design Contradiction:

TemperatureVSObject-affected harmful factors

Solution Approach 1:

The patent introduces an RC snubber circuit as an intermediary element between the MOSFET and the driver. This snubber circuit absorbs the voltage spike energy and prevents it from reaching the driver, allowing the MOSFET to be positioned away from the driver for thermal management while protecting the driver from excessive voltage spikes.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The RC snubber circuit is placed in parallel with the MOSFET to provide beforehand cushioning against voltage spikes. The capacitor in the snubber circuit charges during normal operation and discharges during switching transitions, cushioning the voltage spike before it can damage the driver.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

2Object-affected harmful factors

If MOSFETs are placed close to the driver, then gate drive inductance is reduced minimizing voltage spikes, but thermal management becomes difficult

Engineering Contradiction:

Improvevoltage spikeVSAvoidthermal management

Core Design Contradiction:

Object-affected harmful factorsVSTemperature

Solution Approach 1:

The RC snubber circuit serves as a mediator that allows the MOSFET to be positioned away from the driver for thermal management. The snubber absorbs the inductive kickback, making the gate drive inductance less critical while enabling proper thermal separation.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Temperature

If gate drive distance is increased to separate MOSFETs from driver, then thermal restrictions are satisfied, but voltage spike exceeds driver part ratings

Engineering Contradiction:

Improvethermal restriction complianceVSAvoiddriver rating compliance

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The RC snubber circuit acts as a protective intermediary that allows increased gate drive distance for thermal management. The snubber circuit absorbs the voltage spike energy generated by the increased inductance, ensuring the driver remains within its rating limits even with longer trace lengths.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the electrical parameters of the gate drive path by introducing the RC snubber circuit. This modifies the voltage waveform characteristics, reducing the peak voltage and extending the allowable gate drive distance while maintaining driver reliability.

Inventive Principle:

Principle #35Parameter changes

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

The solution effectively reduces spike levels to within operational parameters, enabling MOSFETs to be spaced farther from the microchip without exceeding driver rating limits, as demonstrated by reducing the offset voltage from negative 7.2 volts to approximately negative 2 volts.

Implementation Method 1

providing a voltage from the junction of source of the high side MOSFET and drain of the low side MOSFET through a resistor-capacitor (RC) circuit connected to the high side source pin of the micro chip

Methodology Applied

Scientific EffectRC filtering: Filter (electronic)

Implementation Method 2

a ferrite bead-capacitor circuit connected to a high side MOSFET source pin of the microchip and to a junction of source of the high side MOSFET and drain of the low side MOSFET

Methodology Applied

Scientific EffectFerrite bead filtering: Absorption (EM radiation)

Data Source

PatentUS8861145B2Circuit with motor driver spike suppression

Publication Date: 2014.10.14 HONEYWELL INTERNATIONAL INC

AI summary

A suppression circuit may be added to a motor driver circuit, which suppresses offset voltage and ringing in the output signal. The suppression circuit may include an RC circuit filter connected to a pin of a microchip providing a gating reference signal and a junction between high and low side MOSFETS connected to the microchip.