Drive Circuit Dynamic Output Current for Switching Loss Reduction

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Solution Overview

Problem

Conventional drive circuits in power modules face challenges in reducing switching loss while minimizing power consumption and avoiding increased switching noise, particularly at high voltage levels like 600 V or 1200 V, due to limitations in output current capacity and resistor-based voltage division methods.

Innovation Solution

A drive circuit design that incorporates a capacitor connected to the high side main terminal of a switching device, where the control circuit increases output current capacity when the input signal turns on and the capacitor voltage drops, effectively reducing switching loss and minimizing power consumption without significant noise increase.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the output current capacity of the control circuit is increased to shorten the Miller period and reduce switching loss, then switching loss is reduced, but switching noise increases due to rapid collector current flow

Engineering Contradiction:

Improveswitching lossVSAvoidswitching noise

Core Design Contradiction:

Loss of energyVSObject-generated harmful factors

Solution Approach 1:

The control circuit dynamically adjusts its output current capacity based on the switching state. During the Miller period when the collector voltage drops, the control circuit increases output current capacity to shorten the Miller period and reduce switching loss. When the switching device is stable ON or OFF, the output current capacity returns to normal levels, preventing excessive current surge and reducing switching noise. This dynamic adjustment resolves the contradiction between reducing switching loss and minimizing switching noise.

Inventive Principle:

Principle #15Dynamics

2Measurement precision

If resistors are used to divide collector voltage for control circuit input, then voltage detection is enabled, but power consumption increases at high voltage levels (600V or 1200V)

Engineering Contradiction:

Improvevoltage detectionVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by stationary object

Solution Approach 1:

A capacitor is introduced as an intermediary component between the collector and the control circuit. The capacitor couples the collector voltage to the control circuit during switching transitions, enabling voltage detection without requiring continuous current flow through high-value resistors. This capacitor-based approach maintains voltage detection capability while significantly reducing power consumption at high voltage levels.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Use of energy by stationary object

If resistance value is increased to reduce current through voltage division resistor, then power consumption decreases, but CR time constant increases and response speed decreases

Engineering Contradiction:

Improvepower consumptionVSAvoidresponse speed

Core Design Contradiction:

Use of energy by stationary objectVSSpeed

Solution Approach 1:

The control circuit dynamically adjusts its input impedance based on the switching state. During the Miller period when rapid voltage changes occur, the control circuit presents a low impedance state, ensuring fast response speed and quick detection of voltage transitions. During stable states, the input impedance increases, reducing power consumption. This dynamic impedance adjustment resolves the contradiction between response speed and power consumption.

Inventive Principle:

Principle #15Dynamics

4Use of energy by stationary object

If resistance value is increased to reduce current, then power consumption decreases, but variation range of divided voltage decreases and detection sensibility is compromised

Engineering Contradiction:

Improvepower consumptionVSAvoiddetection sensibility

Core Design Contradiction:

Use of energy by stationary objectVSMeasurement precision

Solution Approach 1:

The capacitor serves as an intermediary that preserves the full voltage variation range from the collector to the control circuit during switching transitions. Unlike resistor-based voltage division which attenuates the signal, the capacitor couples the complete voltage swing, maintaining detection sensibility. Simultaneously, the capacitor draws minimal steady-state current, reducing power consumption while preserving detection capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 sufficiently reduces switching loss while minimizing power consumption and avoiding increased switching noise, even at high voltage levels, by efficiently managing the Miller period and collector current flow.

Implementation Method 1

a capacitor having one end connected to a high side main terminal of the switching device

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

voltage at the other end of the capacitor drops

Methodology Applied

Scientific EffectVoltage detection:

Data Source

PatentUS10862479B2Drive circuit, power module and electric power conversion system

Publication Date: 2020.12.08 MITSUBISHI ELECTRIC CORP

AI summary

A drive circuit includes: a control circuit providing control voltage to a control terminal of a switching device in accordance with input signal; and a capacitor having one end connected to a high side main terminal of the switching device, wherein the control circuit increases an output current capacity of the control circuit when the input signal becomes ON signal and voltage at the other end of the capacitor drops.