IGBTTutorial资源-CSDN文库

IGBT资料

需积分: 10 82 浏览量 2010-03-11 18:44:24 上传评论 2 收藏 245KB PDF 举报

资源推荐

资源详情

资源评论

Application Note

APT0201 Rev. B

July 1, 2002

IGBT Tutorial

Jonathan Dodge, P.E.

Senior Applications Engineer

John Hess

Vice President, Marketing

Advanced Power Technology

405 S.W. Columbia Street

Bend, OR 97702

Introduction

With the combination of an easily driven MOS gate

and low conduction loss, IGBTs quickly displaced

power bipolar transistors as the device of choice for

high current and high voltage applications. The

balance in tradeoffs between switching speed,

conduction loss, and ruggedness is now being ever

finely tuned so that IGBTs are encroaching upon the

high frequency, high efficiency domain of power

MOSFETs. In fact, the industry trend is for IGBTs to

replace power MOSFETs except in very low current

applications. To help understand the tradeoffs and to

help circuit designers with IGBT device selection and

application, this application note provides a relatively

painless overview of IGBT technology and a

walkthrough of Advanced Power Technology IGBT

datasheet information.

How to Select an IGBT

This section is intentionally placed before the technical

discourse. Answers to the following set of burning

questions will help determine which IGBT is

appropriate for a particular application. The

differences between Non Punch-Through (NPT) and

Punch-Through (PT) devices as well as terms and

graphs will be explained later.

1. What is the operating voltage? The highest

voltage the IGBT has to block should be no more

than 80% of the V

CES

rating.

2. Is it hard or soft switched? A PT device is better

suited for soft switching due to reduced tail

current, however a NPT device will also work.

3. What is the current that will flow through the

device? The first two numbers in the part number

give a rough indication of the usable current. For

hard switching applications, the usable frequency

versus current graph is helpful in determining

whether a device will fit the application.

Differences between datasheet test conditions and

the application should be taken into account, and

an example of how to do this will be given later.

For soft switching applications, the I

rating could

be used as a starting point.

4. What is the desired switching speed? If the

answer is “the higher, the better”, then a PT device

is the best choice. Again, the usable frequency

versus current graph can help answer this question

for hard switching applications.

5. Is short circuit withstand capability required? For

applications such as motor drives, the answer is

yes, and the switching frequency also tends to be

relatively low. An NPT device would be required.

Switch mode power supplies often don’t require

short circuit capability.

IGBT Overview

n+ n+

p+ Substrate (injecting layer)

Buffer layer (PT IGBT)

Drift region

Body region

Emitter

Gate

Collector

N-channel

MOSFET

structure

Figure 1 N-Channel IGBT Cross Section

An N-channel IGBT is basically an N-channel power

MOSFET constructed on a p-type substrate, as

illustrated by the generic IGBT cross section in Figure

1. (PT IGBTs have an additional n+ layer as well as

will be explained.) Consequently, operation of an

IGBT is very similar to a power MOSFET. A positive

voltage applied from the emitter to gate terminals

causes electrons to be drawn toward the gate terminal

in the body region. If the gate-emitter voltage is at or

above what is called the threshold voltage, enough

electrons are drawn toward the gate to form a

conductive channel across the body region, allowing

current to flow from the collector to the emitter. (To

be precise, it allows electrons to flow from the emitter

to the collector.) This flow of electrons draws positive

ions, or holes, from the p-type substrate into the drift

region toward the emitter. This leads to a couple of

simplified equivalent circuits for an IGBT as shown in

Figure 2.

Collector

Emitter

Gate

Collector

Emitter

Gate

Figure 2 IGBT Simplified Equivalent Circuits

The first circuit shows an N-channel power MOSFET

driving a wide base PNP bipolar transistor in a

Darlington configuration. The second circuit simply

shows a diode in series with the drain of an N-channel

power MOSFET. At first glance, it would seem that

the on state voltage across the IGBT would be one

diode drop higher than for the N-channel power

MOSFET by itself. It is true in fact that the on state

voltage across an IGBT is always at least one diode

drop. However, compared to a power MOSFET of the

same die size and operating at the same temperature

and current, an IGBT can have significantly lower on

state voltage. The reason for this is that a MOSFET is

a majority carrier device only. In other words, in an N-

channel MOSFET only electrons flow. As mentioned

before, the p-type substrate in an N-channel IGBT

injects holes into the drift region. Therefore, current

flow in an IGBT is composed of both electrons and

holes. This injection of holes (minority carriers)

significantly reduces the effective resistance to current

flow in the drift region. Stated otherwise, hole

injection significantly increases the conductivity, or the

conductivity is modulated. The resulting reduction in

on state voltage is the main advantage of IGBTs over

power MOSFETs.

Nothing comes for free of course, and the price for

lower on state voltage is slower switching speed,

especially at turn-off. The reason for this is that during

turn-off the electron flow can be stopped rather

abruptly, just as in a power MOSFET, by reducing the

gate-emitter voltage below the threshold voltage.

However, holes are left in the drift region, and there is

no way to remove them except by voltage gradient and

recombination. The IGBT exhibits a tail current during

turn-off until all the holes are swept out or recombined.

The rate of recombination can be controlled, which is

the purpose of the n+ buffer layer shown in Figure 1.

This buffer layer quickly absorbs trapped holes during

turn-off. Not all IGBTs incorporate an n+ buffer layer;

those that do are called punch-through (PT), those that

do not are called non punch-through (NPT). PT IGBTs

are sometimes referred to as asymmetrical, and NPT as

symmetrical.

The other price for lower on state voltage is the

possibility of latchup if the IGBT is operated well

outside the datasheet ratings. Latchup is a failure mode

where the IGBT can no longer be turned off by the

gate. Latchup can be induced in any IGBT through

misuse. Thus the latchup failure mechanism in IGBTs

warrants some explanation.

The basic structure of an IGBT resembles a thyristor,

namely a series of PNPN junctions. This can be

explained by analyzing a more detailed equivalent

circuit model for an IGBT shown in Figure 3.

Drift region

resistance

Body region

spreading

resistance

Collector

Emitter

Gate

Parasitic

NPN

Parasitic

thyristor

Figure 3 IGBT Model Showing Parasitic Thyristor

A parasitic NPN bipolar transistor exists within all N-

channel power MOSFETS and consequently all N-

channel IGBTs. The base of this transistor is the body

region, which is shorted to the emitter to prevent it

from turning on. Note however that the body region

has some resistance, called body region spreading

resistance, as shown in Figure 3. The P-type substrate

and drift and body regions form the PNP portion of the

IGBT. The PNPN structure forms a parasitic thyristor.

If the parasitic NPN transistor ever turns on and the

sum of the gains of the NPN and PNP transistors are

greater than one, latchup occurs. Latchup is avoided

through design of the IGBT by optimizing the doping

levels and geometries of the various regions shown in

Figure 1.

The gains of the PNP and NPN transistors are set so

that their sum is less than one. As temperature

increases, the PNP and NPN gains increase, as well as

the body region spreading resistance. Very high

collector current can cause sufficient voltage drop

across the body region to turn on the parasitic NPN

transistor, and excessive localized heating of the die

increases the parasitic transistor gains so their sum

exceeds one. If this happens, the parasitic thyristor

latches on, and the IGBT cannot be turned off by the

gate and may be destroyed due to over-current heating.

This is static latchup. High dv/dt during turn-off

combined with excessive collector current can also

effectively increase gains and turn on the parasitic

NPN transistor. This is dynamic latchup, which is

actually what limits the safe operating area since it can

happen at a much lower collector current than static

latchup, and it depends on the turn-off dv/dt. By

staying within the maximum current and safe operating

area ratings, static and dynamic latchup are avoided

regardless of turn-off dv/dt. Note that turn-on and

turn-off dv/dt, overshoot, and ringing can be set by an

external gate resistor (as well as by stray inductance in

the circuit layout).

PT versus NPT Technology

Conduction Loss

For a given switching speed, NPT technology generally

has a higher V

CE(on)

than PT technology. This

difference is magnified further by fact that V

CE(on)

increases with temperature for NPT (positive

temperature coefficient), whereas V

CE(on)

decreases

with temperature for PT (negative temperature

coefficient). However, for any IGBT, whether PT or

NPT, switching loss is traded off against V

CE(on)

Higher speed IGBTs have a higher V

CE(on)

; lower speed

IGBTs have a lower V

CE(on)

. In fact, it is possible that a

very fast PT device can have a higher V

CE(on)

than a

NPT device of slower switching speed.

Switching Loss

For a given V

CE(on)

, PT IGBTs have a higher speed

switching capability with lower total switching energy.

This is due to higher gain and minority carrier lifetime

reduction, which quenches the tail current.

Ruggedness

NPT IGBTs are typically short circuit rated while PT

devices often are not, and NPT IGBTs can absorb more

avalanche energy than PT IGBTs. NPT technology is

more rugged due to the wider base and lower gain of

the PNP bipolar transistor. This is the main advantage

gained by trading off switching speed with NPT

technology. It is difficult to make a PT IGBT with

greater than 600 Volt V

CES

whereas it is easily done

with NPT technology. Advanced Power Technology

does offer a series of very fast 1200 Volt PT IGBTs,

the Power MOS 7 IGBT series.

Temperature Effects

For both PT and NPT IGBTs, turn-on switching speed

and loss are practically unaffected by temperature.

Reverse recovery current in a diode however increases

with temperature, so temperature effects of an external

diode in the power circuit affect IGBT turn-on loss.

For NPT IGBTs, turn-off speed and switching loss

remain relatively constant over the operating

temperature range. For PT IGBTs, turn-off speed

degrades and switching loss consequently increases

with temperature. However, switching loss is low to

begin with due to tail current quenching.

As mentioned previously, NPT IGBTs typically have a

positive temperature coefficient, which makes them

well suited for paralleling. A positive temperature

coefficient is desirable for paralleling devices because

a hot device will conduct less current than a cooler

device, so all the parallel devices tend to naturally

share current. It is a misconception however that PT

IGBTs cannot be paralleled because of their negative

temperature coefficient. PT IGBTs can be paralleled

because of the following:

• Their temperature coefficients tend to be almost

zero and are sometimes positive at higher current.

• Heat sharing through the heat sink tends to force

devices to share current because a hot device will

heat its neighbors, thus lowering their on voltage.

• Parameters that affect the temperature coefficient

tend to be well matched between devices.

IGBTs from Advanced Power Technology

Advanced Power Technology offers three series of

IGBTs to cover a broad range of applications:

剩余14页未读，继续阅读

评论收藏

内容反馈

iskusa

粉丝: 1
资源: 2

IGBT Tutorial

Tutorial

IGBT基本原理

ANSYS Fluent Tutorial Guide 19.2 教程 官方案例 tutorial 典例

FLUENT 2020R2 tutorial guide PDF及案例源文件

OpenGL ES Tutorial for Android.zip

热设计IGBT

IGBT的作用

IGBT Selection

英飞凌IGBT

STM32F1_Tutorial

operating_system_tutorial.pdf

J2EE Tutorial中文版

Spring教程 spring tutorial

TUTORIAL_GML

gtk+2.0 tutorial

FFT Tutorial

Unity3D Tutorial

IGBT Selection54

IRG4PC50UD IGBT

Tutorial-4

tutorial代码

java tutorial

Computational Fourier Optics a MATLAB tutorial

opencv tutorial_code

J2EE tutorial 中文版

最新资源

ANSYS Fluent Tutorial Guide 19.2 教程官方案例 tutorial 典例