Amritesh Report

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A PROJECT REPORT

ON

IGBT GATE DRIVER CIRCUIT

SUBMITTED BY

AMRITESH KUMAR

2009H131076P

M.E ELECTRICAL (POWER ELECTRONICS AND DRIVES)

AT

CROMPTON GREAVES LIMTED, NAVI MUMBAI

A Practice School II station of

BIRLA INSTITUTE OF TECHNOLOGY AND SCIENCE

BITS-PILANI, RAJASTHAN -333031

JUNE- 2011


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A PROJECT REPORT

ON

IGBT GATE DRIVER CIRCUIT

(With Reference to Crompton Greaves limited, Mahape- Navi Mumbai)

SUBMITTED BY

AMRITESH KUMAR

2009H131076P

M.E ELECTRICAL (POWER ELECTRONICS AND DRIVES)

Prepared in Partial Fulfilment of the

PRACTICE SCHOOL II

COURSE NO:BITS C412

AT

CROMPTON GREAVES LIMTED, NAVI MUMBAI

A Practice School II station of

BIRLA INSTITUTE OF TECHNOLOGY AND SCIENCE

BITS-PILANI, RAJASTHAN -333031

JUNE- 2011


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ACKNOWLEDGEMENT

I am really grateful to convey my heartily greetings to my well wisherDr. Sri Raghvan-

Consultant CROMPTON GREAVESLTD for giving me the opportunity to work with his

team and encouraging myself by having faith in me, helping me in developing my knowledge

and for the contribution towards the company with his support and valuable guidance in

doing this project.

I feel delighted in expressing my deep sense of gratitude to Mr. Sanjay Ostwal-

A.G.Mfor their guidance in doing this project.

I am thankful to each of the employees at CROMPTON GREAVES LIMITED-

Mahape plant for their coordination in helping me with providing the details of this project

with their guidance and support in the precise direction for developing my knowledge.

Finally my heartiest thanks go to PS Faculty Mr Shashank Belsare, for his constantsupport and encouragement throughout the program, and his invaluable suggestions.

Amritesh Kumar

IDNO: (2009H131076P)

ME Power Electronics and drives Engineering


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BIRLA INSTITUTE OF TECHNOLOGY AND SCIENCE -PILANI (RAJASTHAN)

PRACTICE SCHOOL DIVISION

Station: CROMPTON GREAVES LIMITED. Centre:MUMBAI

ID No. & Name:2009H131076P AMRITESH KUMAR

Title of the Project:IGBT GATE DRIVE CRICUIT

Duration: 5 Months Date of Start: 6th JAN -2011

Date of submission: 17th JUNE 2011

Name /ID NO/Discipline:

AMRITESH KUMAR 2009H131076P, POWER ELECTRONICS AND DRIVESENGINEERING

Name & designation of the Experts:

o Dr .Sri Raghvan, Consultant, PhD(IIT BOMBAY)Electrical Engineering

o Mr Sanjay Ostwal, AGM, Crompton Greaves Ltd.

Name of the PS Faculty:Mr Shashank Belsare,

ABSTRACT:

A comprehensive report has been made about IGBT gate driver circuit. This report

deals with various aspects of a typical driver circuit. Different types of Gate Drivers are being

made by different Companies like Semikron, Infieneon, CT CONCEPT etc. As the industry

pushes for higher power levels and higher switching frequencies, power supplies, which for

us IGBTs for power conversion, are being designed to their ultimate attainable efficiency,

smallest footprint, size and weight. The subject of driving IGBTs to their highest possible

frequencies at the highest possible power levels, still providing protection, is multi -

dimensional and requires knowledge of IGBTs as well as circuit theory and how it applies to

this discipline. The project deals with this subject and explains different types of gate driver

using opto coupler, fibre optics, transformer as an isolation part in different drivers. For each

type prototype has been made to experimentally verify the result and also full design has been

given.

Finally the suggestions are given with detail analytical proofs so as to make an

attempt to replace the existing GTO based converter in traction with IGBT modules.

Regards............

Signature of Student Signature of PS Faculty

Date: Date:


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BIRLA INSTITUTE OF TECHNOLOGY AND SCIENCE -PILANI (RAJASTHAN)

PRACTICE SCHOOL DIVISION

Response Option Sheet

ID No. & Name:2009H131075P AMRITESH KUMAR

Title of the Project: IGBT GATE DRIVER

Course No. and Course Name: BITS C412 PRACTICE SCHOOL II

Code No. Response Option Course No.(s) & Name

1. A new course can be designed out of this project.NO

2. The project can help modification of the course content of some of

the existing Courses YES

3. The project can be used directly in some of the existing

Compulsory Discipline Courses (CDC)/ Discipline Courses Other

than Compulsory (DCOC)/ Emerging Area (EA), etc. Courses

NO

4. The project can be used in preparatory courses like Analysis and

Application Oriented Courses (AAOC)/ Engineering Science

(ES)/ Technical Art (TA) and Core Courses.

NO

5. This project cannot come under any of the above mentioned

options as it relates to the professional work of the host

organization.

NO

_________________ ________________

Signature of Student Signature of Faculty

Date: Date


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CONTENTS PAGE

NO

1. INTRODUCTION1.1About Crompton Greaves Ltd.

1.1.1 Introduction to Crompton Greaves1.1.2 Industrial drives and automation1.1.3 Traction Electronics

2. IGBT Theory3. Introduction To Gate Drive Circuit

3.1 Isolation Circuit3.2 IGBT Driver Design Consideration3.3 Features Of Isolated IGBT Gate Driver

4. Functions of gate drivers4.1 Floating Power Supply4.2 Isolated Supply4.3 Optical Level Shifting By Fibre Optic Link

5. Design5.1 Gate Resistor Design

5.2 Protection Circuit Design

5.3 Optocoupler Triggering Circuit Design

5.4 Fibre Optic Trigger Design

6. CT Concept Core base driver circuit design

7. Results And Observations

7.1 Opto Based Gate Driver

7.1.1 Floating Power Supply(+15/-15)

7.1.2 Floating Power Supply(+17/-7)

7.2 Optocoupler Based Triggering Circuit

7.3 Optical Fibre Based Triggering Circuit

7.4 Protection And Drive Circuit

7.5 Ct Concept Core Based IGBT Driver

7.6 Output Waveforms

7.7 Vce Sat Protection Testing

8. Experimental Setups

CONCLUSION

APPENDICES

REFERENCES

1-2

3

4-14

15-17

18-24

25-30

31-38

39-40

41

42-49

50


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1.INTRODUCTION1.1About Crompton Greaves ltd1.1.1 Introduction to Crompton Greaves

As one of the world`s leading engineering corporations, CG provides end-to-end solutions,

helping its customers use electrical power effectively and increase industrial productivity with

sustainability. CG was established in 1937 in India; and, since then the Company has been a

pioneer and has retained its leadership position in the management and application of electrical

energy .Crompton Greaves (CG) is part of the US$ 4 bn Avantha Group, a conglomerate with an

impressive global footprint, operating in over 10 countries. Since its inception, CG has been

synonymous with electricity. In 1875, a Crompton 'dynamo' powered the world's very first

electricity-lit house in Colchester, Essex, U.K. CG's India operations were established in 1937,

and since then the company has retained its leadership position in the management and

application of electrical energy.

Today, Crompton Greaves is India's largest private sector enterprise. It has diversified

extensively and is engaged in designing, manufacturing and marketing technologically advanced

electrical products and services related to power generation, transmission and distribution,

besides executing turnkey projects. The company is customer-centric in its focus and is the

single largest source for a wide variety of electrical equipments and products.

In April 2010 the company acquired three business of NELCO A Tata Enterprise on a going

concern basis. These businesses are Industrial Drives and Automation, Traction Electronics and

Industrial and Railways SCADA. The company manages these businesses from its DTS (Drives,

Traction and SCADA) unit situated at Mahape

1.1.2 Industrial Drives and Automation

Drives & Automation division is one of the major business activities of CG (DTS). Electrical

drives form the basic constituent of any manufacturing process provides the turn key solutions

for the requirement of the process industries. For providing the solutions in DC Drives, CG has

tied up with M/s. AVTRON Inc of United States of America, for the microprocessor based

digital drive regulator for DC thyristor drives. CG has acquired the know-how of the dc drive

regulator, for using it with CGs own range of thyristor Converters. This technology has been

indigenized by CG, and the controller Addvantage32 is being manufactured at CGs Mahape

works. This provides economic solution for the end user, as only necessary components are

imported for making the drive. This is integrated with CGs Own range of Bridges. A range of

thyristor converters spanning various voltages and current ratings are available from CG, to suit

for the motor ratings of the user. CG provides the tailor made solutions as per the users process

requirements.

In the LV AC drives, CG has tied up with M/s EEI S.r.I. Italy. This includes 415V & 690V

drive solutions from 200 KW to 1.5 MW. We address solutions, as in DC Drives, but with theInverter module imported totally from EEI. The System and panel Engineering is added locally

to complete and build the total System. CG has collaborated with M/s Beijing leader & Harvest


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Electric Technologies Co Ltd. for medium Voltage Range of Inverter Drive Systems. These

drives are available from 500 KW to 10 MW and from 3 KV to 11 KV inputs and outputs.

These drives are used mostly in the Energy saving and Consumption- reductions sectors, where

a large amount of energy saving is achieved. CG imports the total drive modules, value adding

any peripherals to support the systems. Where test benches are required, using such drives, thesedrives are tailored made to suit to the process requirements.

For solutions in Automation, to integrate with the DC and AC drives above, CG integrates the

best & latest technologies available at that moment of time. Industrial automation products from

GE Fanuc, Allen-Bradley, etc are regularly used for resolving challenges on the process field.

Programmable Logic Controllers like Versa ax, 90-30, SLC5/04, PLC5/40, Control Logics etc.

have been provided by CG to resolve complex algorithms in industry. User interface is the

utmost important thing in todays industrial automation world today. Human Machine Interface

graphic GUI products like Complicity, Intellection, National Instruments, etc. have been

provided by CG, to make the machine operator, best understand the process.

Other peripherals of the drives, like Motor Mounted Devices and Field Mounted Devices to

complete the total Solution, including test beds, couplings, mounting flange arrangements,

torque sensors, Motors, etc can also be provided, along with the drives.

1.1.3 Traction Electronics

Indian Railways (IR) received the technology from ABB Switzerland for manufacturing modern

and efficient 3 phase AC Loco in India in year 1998. IR was looking for Indian Transfer of

Technology (ToT) partners for manufacturing Converters, Electronics, Motors and

Transformers used in this loco being manufactured at Chittaranjan Locomotive Works (CLW)

near Kolkata.

A core team from the Drives and Automation Group was formed in year 1999 to cater to the

needs IR/CLW. There was a ToT (Transfer of Technology) and as a part of this ToT,

manufacturing and Testing Documents were provided by IR. Also the technical team was sent to

ABB Switzerland for hands-on experience on Manufacturing and testing processes of the

Converters. Based on the documents and hands on training experiences the complete

manufacturing and testing set-up was installed at Mahape.

Power Converter, Auxiliary Converters and Control Electronics are manufactured and supplied

to CLW. Also various repairs and supply of spares orders from different Loco maintenance

sheds are executed by us on regular basis. Quality and cost are monitored with control on

procedures and regular review of Indigenization processes.

Also we are venturing into other related products and markets e.g. IGBT based converters, open

control system, Metro converters, Diesel Loco converters etc. For these new products we have

technical tie-ups with Trainees-Spain.


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2. IGBT Theory

It is a three-terminal power semiconductor switch used to control the electrical energy. Many

new applications would not be economically feasible without IGBTs. Prior to the advent of

IGBT, power bipolar junction transistors (BJT) and power metal oxide field effect transistors

(MOSFET) were widely used in low to medium power and high-frequency applications, where

the speed of gate turn-off thyristors was not adequate. MOSFET causes inferior conduction

characteristics as the voltage rating is increased above 200V. Therefore their on-state resistance

increases with increasing breakdown voltage. Furthermore, as the voltage rating increases the

inherent body diode shows inferior reverse recovery characteristics, which leads to higher

switching losses In order to improve the power device performance, it is advantageous to have

the low on-state resistance of power BJTs with an insulated gate input like that of a powerMOSFET The Darlington configuration of the two devices shown has superior characteristics as

compared to the two discrete devices.

Compared to power MOSFETs the absence of the integral body diode can be considered as an

advantage or disadvantage depending on the switching speed and current requirements An

external fast recovery diode or a diode in the same package can be used for specific applications.

The IGBTs are replacing MOSFETs in high-voltage applications with lower conduction losses.

They have on-state voltage and current density comparable to a power BJT with higher

switching frequency. Although they exhibit fast turn-on, their turn-off is slower than a MOSFET

because of current fall time. The IGBTs have considerably less silicon area than similar rated

power MOSFETs. Therefore by replacing power MOSFETs with IGBTs, the efficiency is

improved and cost is reduced. IGBT is also known as conductivity modulated FET (COMFET),

insulated gate transistor (IGT), and bipolar-mode MOSFET. As soft switching topologies offer

numerous advantages over the hard switching topologies, their use is increasing in the industry.

By the use of soft-switching techniques, IGBTs can operate at frequencies up to hundreds of

kilohertz. The IGBTs behave differently under soft switching condition as opposed to hard

switching conditions. Development of the model can follow only after the physics of device

operation under stress conditions imposed by the circuit is properly understood.

IGBTs in high power converters subjects them to high-transient electrical stress such as short

circuit and turn-off under clamped inductive load and therefore robustness of IGBTs under

stress Conditions is an important requirement.


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3. Introduction to Gate Drive Circuit

A gate signal is required for every power semiconductor-controlled device to bring it into the

conduction state. However, the nature of the gate drive requirement (or the base drive

requirement for power bipolar junction transistor (BJT) and Darlington power transistor) of each

device varies, depending on the voltage and current rating and also on the type of the device.The gate drive requirements of thyristors (silicon controlled rectifier, SCR), Triac, etc. are

different from the gate drive requirements of the gate-commutation devices, viz. gate-turn-off

thyristor (GTO), power BJT, metal-oxide field effect transistor (MOSFET), insulated-gate

bipolar transistor(IGBT),

Global trends towards energy efficiency over the last three decades have facilitated the need for

technological advancements in the design and control of power electronic converters for energy

processing. These power electronic converters find widespread applications in industry such as:

Consumer electronics

Battery chargers for cellular telephones and cameras Computer power supplies

Automobile industries

Electronic ignitions and lighting

Commercial sectors

Variable speed motor drives for conveyor belt systems

Induction heating installations for metals processing

Uninterruptible power supplies (UPS)

Industrial welding

The dynamic behaviour of power semiconductors is usually a major factor in determining power

converter performance. Speed limitations can lead to limits on duty ratios and switching

frequencies .Switching loss can be high in fast converters. The basic concern is how to translate

the information the information in a switching function into the actual device function. The gate

drives, the key circuits for this translation. The term is generic, and include fast amplifier to

drive IGBT. Switch isolation is crucial but often neglected issue. The primary function of a gate

drive circuit is to switch a power semiconductor device from the off state to the on state and vice

versa. In most situations the designer seeks low cost drive circuits that minimizes the turn on

and turn off times so that the power device spends a little time in traversing the active region

where the instantaneous power dissipation is large. In the on state the drive circuit should

provide adequate drive power to keep the power switch in the on state where the conductionlosses are low. Very often the drive circuit must provide reverse bias to the power switch control

terminals to minimize turn off times and to ensure that the device remains off-state and is not

triggered on by the switching of the other power devices.

The major contributors are the parasitic gate inductance (Lg) and parasitic source inductance

(Ls). At high frequency, Lg will present large impedance that will isolate the driver from the

gate electrode of the IGBT die. High switching speed means high di/dt through IGBT source

and drain, which will create a large voltage drop across Ls. This voltage can be higher than the

gate driver voltage and will eventually turn off the device. This negative feedback can drive the

IGBT into an oscillatory state. A damping resistor is normally inserted in series with the gateelectrode to prevent such oscillations; however, this further impedes the transfer of charge to the

gate.


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The device circuit is the interface between the control circuit and the power switch. The drive

circuits amplifies the control signals to levels required to drive the power switch and provides

electrical isolation when required between the power switch And the logic level signal

processing and control circuits. Often the drive has significant power capabilities compared to

the logic level control/signal processing circuits. The basic topology of the drive circuit isdictated by three functional considerations. First is the output signal provided by the drive

circuits? Second, can the drive signals be directly coupled to the power switch, or is electrical

isolation required between the logic level control circuits and the power device. Third is weather

the output of the driver circuit is connected in series or in parallel to the power switch.

Additional functionality may be required of the drive circuit, which will further influence the

topological details of the circuit. Provisions may be included in the drive circuit design for

protection of the power switch from over currents. Then commutation between the drive circuit

and the commutation circuit is needed. A gate signal is required for every power semiconductor

controlled device to bring it into the conduction state. However, the nature of the gate drive

requirement (or the base drive requirement for power bipolar junction transistor (BJT) and

Darlington power transistor) of each device varies, depending on the voltage and current rating

and also on the type of the device (i.e., thyristors or gate-commutation devices). The gate drive

requirements of thyristors (silicon controlled rectifier, SCR), Triac, etc. are different from the

gate drive requirements of the gate-commutation devices, viz. gate- turn-off thyristor (GTO),

power BJT, metal-oxide field effect transistor (MOSFET), insulated-gate bipolar transistor

(IGBT), static induction transistor (SIT), MOS-controlled thyristor (MCT), and so forth.

Therefore, gate drive circuits of thyristors and gate-commutation devices are discussed here

separately. The gate drive circuit acts as an interface between the logic signals of the controller

and the gate signals of the IGBT, which reproduces the commanded switching function at ahigher power level. Non-ideal ties of the IGBT such as finite voltage and current rise and fall

times, turn-on delay, voltage and current overshoots, and parasitic components of the circuit

cause differences between the commanded and real waveforms. Gate drive characteristics affect

the IGBT non-idealities. The MOSFET portion of the IGBT drives the base of the pnp transistor

and therefore the turn-on transient and losses is greatly affected by the gate drive. Due to lower

switching losses, soft-switched power converters require gate drives with higher power ratings.

The IGBT gate drive must have sufficient peak current capability to provide the required gate

charge for zero current switching and zero voltage switching. The delay of the input signal to

the gate drive should be small compared to the IGBT switching period and therefore, the gate

drive speed should be designed properly to be able to use the advantages of faster switching

speeds of the new generation IGBTs.

But the turn-off switching of IGBT depends on the bipolar characteristics. Carrier lifetime

determines the rate at which the minority carriers stored in the drift region recombine. The

charge removed from the gate during turn-off has small influence on minority carrier

recombination. The tail current and di/dt during turn-off, which determine the turn-off losses,

depend mostly on the amount of stored charge and the minority carriers lifetime. Therefore, the

gate drive circuit has a minor influence on turn-off losses of the IGBT, while it affects the turn-

on switching losses.

The turn-on transient is improved by use of the circuit shown. The additional current source


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increases the gate current during the tail voltage time, and therefore reduces the turn-on loss.

The initial gate current is determined by Vgg + and Rgon, which are chosen to satisfy device

electrical specifications and EMI requirements. After the collector current reaches its maximum

value, the miller effect occurs and the controlled current source is enabled to increase the gate

current to increase the rate of collector voltage fall. This reduces the turn-on switching loss.Turn-off losses can only be reduced during the miller effect and MOS turn-off portion of the

turn off transient, by reducing the gate resistance. But this increases the rate of change of

collector voltage, which strongly affects the IGBT latching current.

A simple IGBT gate drive

The additional current source increases the gate current during the tail voltage time,

and therefore reduces the turn-on loss. The initial gate current is determined by Vgg + and

Rgon, which are chosen to satisfy device electrical specifications and EMI requirements. After

the collector current reaches its maximum value, the miller effect occurs and the controlled

current source is enabled to increase the gate current to increase the rate of collector voltage fall.

This reduces the turn-on switching loss. Turn-off losses can only be reduced during the miller

effect and MOS turn-off portion of the turn off transient, by reducing the gate resistance. But

this increases the rate of change of collector voltage, which strongly affects the IGBT latching

current and RBSOA.

3.1 Isolation Circuit

Major requirement of any driver circuit is to provide isolation between power circuit and lowvoltage side of driver circuit. This major task is being provided by mainly three ways:

1) OPTOCOUPLER

2) FIBER OPTICS

3) TRANSFORMER

The basic ways to provide electrical isolation are optocouplers fibre optics and transformers.

The optocoupler consists of a light emitting diode the optical transistor and a built in Schmitt

trigger. A positive signal from the control logic causes the LED to emit light that is focused on

the optically sensitive base region of the photo transistor. The light falling on the base region


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causes the photo transistor to turn on. The resulting drop in voltage at the photo transistor causes

the Schmitt trigger to change state. The output of the Schmitt trigger is the optocoupler output

and can be used as the control input to the isolated drive circuit. The capacitance between the

LED and the base of the receiving transistor within the opto coupler should be as small as

possible to avoid retriggering at both turn on and turn off of the power transistor due to the jumpin the potential between the power transistor emitter reference point and the ground of the

control electronics. To reduce this problem, optocouplers with electrical shield between the LED

and the receiver transistor should be used.

As an alternative fibre optics can be used to completely to eliminate the retriggering problem

and to provide very high electrical isolation and creep age distance. When using fibre optic

cables, the LED is kept on the printed circuit board of the control electronics, and the optical

fibre transmits the signals to the receiver transistor, which is put on the drive circuit printed

circuit printed circuit board.

Instead of using optocoupler or fibre optic cables, the control signal can be coupled to the

electrically isolated drive circuit by means of a transformer. If the switching frequency is high

(several tens of kilohertz) and the frequency is high and the duty ratio D varies only slightly

around 0.5 a baseband control signal of appropriate magnitude can be applied directly to the

primary of a relatively small and lightweight pulse transform and the secondary output can be

used to either directly drive the power switch or used as the input to an isolated drive circuit. As

the switching frequency is decreased below tens of kilohertz range, a baseband control signal

directly applied to the transformer primary becomes impractical because the size and weight of

the transformer becomes increasingly larger.

GENERAL REQUIRMENT FOR GATE DRIVER FOR HIGH POWER IGBT

MODULES:-

The primary function of the gate drive circuit is to convert logic level control signals into the

appropriate voltage and current for efficient, reliable, switching of the IGBT module. An output

driver stage consisting of small power MOSFETs or bipolar transistors performs the conversion

by alternately connecting the IGBTs gate to the appropriate on ( ) and off ( ) voltages.

The driver stage devices and series gate resistance must be selected to provide the

appropriate peak current for charging and discharging the IGBTs gate. Most gate drive circuits

also provide isolation so that the logic signals are not connected to the dangerous high voltagepresent in the power circuit. The driver must also be immune to the severe electromagnetic noise

produced by the fast switching, high voltage, and high current IGBT power circuit. Careful

layout and component selection is critical to avoid problems with coupled noise.

TURN ON VOLTAGE

In order to establish collector to emitter conduction in an IGBT module a positive voltage must

be applied to the gate. The absolute maximum voltage that can safely be applied to the IGBT's

gate is usually specified on the device data sheet. Modules this voltage is 20V. Application of

voltages greater than 20V may cause breakdown of the gate oxide resulting in permanentdamage to the device. The 20V upper limit must be restricted even further if short circuit


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survival is required. The short circuit withstand time ( ) of a given device is inversely

proportional to the product of applied voltage and short circuit current. The short circuit current

increases with increasing gate voltage thus degrading the withstand time. IGBTs are guaranteed

to survive a low impedance short circuit for 10ms with an applied gate voltage of 15V10%.

The usable lower limit for the on state gate voltage is decided by the devices trans conductanceor gain and acceptable switching losses. For this device it can be seen that a gate voltage of

about 10V is enough to support the devices peak current rating ( = 2 ). A gatevoltage of 10V would be sufficient to fully turn the device on but it may not be sufficient to

obtain efficient switching. If 10 volts were used for a long dynamic saturation (slow turn-

on) will result because the gate voltage takes a long time to reach 10V as it exponentially

charges through the series gate resistance. For optimum performance recommends a turn-on

gate voltage of 15V10%. Using a voltage in this range will ensure that the device stays fully

saturated and switches on efficiently while maintaining good short circuit durability.

TURN OFF VOLTAGE

A substantial off bias of at least -5V is recommended for large IGBT modules. Use of an off

bias voltage will reduce turn-off losses and provide additional dv/dt noise immunity. Large

IGBT modules generally require a stronger off bias than other power MOS devices for two

reasons. First, IGBTs typically operate at higher voltages resulting in increased dv/dt couplingof switching noise. Secondly, large IGBT modules that are constructed from parallel chips have

internal gate resistors in series with each chip. Even if low impedance short is applied at the

modules external terminals, voltage can develop at the gate of the IGBT chip when miller effect

current flows through the internal resistors. For SEMICRON IGBT modules an off bias in the -

5V to -15V range is recommended. Like voltages greater than +20V, voltages more negative

than -20V must be avoided because they may damage the IGBT's gate.

SERIES GATE RESISTANCE

The external series gate resistance (RG) has a significant effect on the IGBT's dynamic

performance. The IGBT is switched on and off by charging and discharging its gate capacitance.

A smaller series gate resistor will charge and discharge the gate capacitance faster resulting in


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increased switching speed and reduced switching losses. In addition to decreased switching

losses a lower series gate resistance also helps to improve dv/dt noise immunity. Smaller series

gate resistors more effectively shunt away miller effect and dv/dt coupled noise currents that

could cause dangerous voltages to appear on the IGBT's gate. The minimum value of the series

gate resistor for turn on is usually limited by the recovery characteristics of the free wheel diode.In hard switching inductive load circuits the di/dt stress at free wheel diode recovery is a

function of the series gate resistance. If the di/dt stress becomes too high the free wheel diode

may become "snappy" resulting in undesirable oscillations, high recovery currents, and transient

voltages. -Series IGBT modules have a newly developed proton beam irradiated soft recovery

diode that virtually eliminates these effects. A larger series gate resistance may be desirable to

help reduce transient voltage during turn-off switching. Unfortunately, in most cases the series

gate resistance must be increased substantially to have any significant impact on the turn-off fall

time. Usually, such an increase in series gate resistance will result in poor dv/it noise immunity

and excessive switching losses. It is usually better to reduce transient voltages with improved

power circuit layout and/or snubber designs. Giving consideration to all of the above issues, a

recommended range of gate resistance for all H-Series and F-Series IGBT modules. The lowest

value in the recommended range is the value used in the conditions for switching times on the

device data sheet. The maximum value is normally ten times the minimum.

When switching, the IGBT consumes power from the gate drive power supply. The amount of

power consumed is a function of operating frequency, on and off bias voltages and total gate

charge. The actual peak current is usually considerably less than this value because the

assumptions made above are not generally true. However, designing the gate drive circuit for

this theoretical maximum output current is usually a good general practice.

NOISE IMMUNITY OF DEIVER

IGBT gate drive circuits are subjected to high common mode dv/dt.

The driver circuit layout must minimize parasitic capacitances between adjacent drive

circuits in order to prevent C x dv/dt coupling of noise.

The isolating interface for the gate drive signals must be designed with appropriate noise

immunity

If a pulse transformer is used, its intertwining capacitance must be small.

If opt couplers are used they must have isolation that is designed for both high commonmode voltage and transient noise immunity.

Opt couplers should have a guaranteed minimum common mode transient noise

immunity of 10kV/ms specified at a common mode voltage ( ) of at least 1000V.

The layout of the isolating interface must minimize parasitic capacitance between the

primary and secondary.

Use of ground plane shield layers can be very helpful in controlling noise coupled

through stray capacitances by the high dv/dt of the power circuit.

If twisted pair gate drive leads are used the pairs should be kept separated from each

other.

If they must be bundled shielded cables with the shield tied to emitter potential of the

IGBT being driven should be used.


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In general minimizing gate drive lead length will help to prevent noise coupling.

Minimum length wiring also helps to achieve the high peak drive currents needed for

efficient switching. The best practice is to mount the driver circuit directly on the IGBT

module.

CONTROL OF ON AND OFF VOLTAGE

Control of the steady-state on and off gate voltage is easily accomplished through

appropriate regulation of the gate drive power supply.

However, during switching, and especially during short circuit operation miller effect

currents cause voltage on the series gate resistor and / voltage on gate driverparasitic inductance.

These voltages can add to the normal on-state gate voltage causing a surge voltage on

the gate. During switching, gate voltage surges must be maintained less than the devices

maximum gate voltage rating (usually 20V). Under short circuit conditions gate voltagesurges will cause degradation of short circuit withstanding capability by allowing higher

than normal currents to flow.

In order to control gate voltage surges it is often desirable to implement gate voltage

clamping on the gate side of the series gate resistor.

The simplest form of the gate voltage clamping is back-to-back zener diodes connected

from gate to emitter.

In order for the gate voltage clamping circuit to be effective it must be connected as

close as possible to the gate and emitter terminals of the IGBT module. For 15V gate

drive 16V to 18V zener is an even more effective. In this circuit the gate voltage is diode

clamped to a local capacitor charged to the turn-on gate voltage. Gate voltage clamping

becomes critical with larger IGBT modules because miller effect currents are more

severe. Long gate drive leads also aggravate gate voltage surges making gate voltage

clamping even more necessary IGBT modules have gate voltage clamping zener built

into the internal RTC circuit. This circuit combined with the lower reverse transfer

capacitance of the trench IGBT chip eliminates the need for external gate voltage

clamping circuits in most applications. The gate drive circuit requires Von and Voff DC

power supplies.

In most high power applications it is necessary to provide isolated power supplies that

can float as needed to the emitter potential of the IGBT being driven. Isolated power

supplies are required for the high side gates in single and three phase inverter circuits

because the emitter potential of the high side IGBT changes when the low side IGBT is

switched.

SHORT CIRCUIT PROTECTION:-

IGBT modules are designed to survive low impedance short circuits for a minimum of 10ms. In

many cases it is desirable to implement the short circuit protection in the gate drive circuit in

order to provide the fast response required for protection against severe low impedance short

circuits. Typically this protection has been provided by collector emitter voltage sensing or socalled desideration detection.


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A high voltage fast recovery diode (D1) is connected to the IGBTs collector to monitor the

collector to emitter voltage. When the IGBT is in the off state, D1 is reverse biased and the (+)

input of the comparator is pulled up to the positive gate drive power supply which is normally

+15V. When the IGBT turns on, the comparators (+) input is pulled down by D1 to the IGBTs

VCE (sat). The (-) input of the comparator is supplied with a fixed voltage (VTRIP) which istypically set at about 8V. During normal switching the comparators output will be high when the

IGBT is off and low when the IGBT is on. If the IGBT turns on into a short circuit, the high

current will cause the collector-emitter voltage to rise above V TRIP even though the gate of the

IGBT is being driven on. This abnormal presence of high VCE when the IGBT is supposed to

be on is often called desaturation. Desideration can be detected by a logical AND of the drivers

input signal and the comparator output. When the output of the AND goes high a short circuit is

indicated. The output of the AND is used to command the IGBT to shut down in order to protect

it from the short circuit. A delay (trip) must be provided after the comparator output to allow for

the normal turn on time of the IGBT. The TRIP delay is set so that the IGBTs Vce has enough

time to fall below VTRIP during normal turn on switching. If trip is set too short, erroneous

desaturation detection will occur. The maximum trip delay is limited by the IGBTs short

circuit withstanding capability.

3.2 IGBT DRIVER DESIGN CONSIDERATION:-

When designing and building driver circuits for an IGBT, the following will need to be taken in

to consideration to prevent unwanted voltage spikes, oscillation or ringing, and false turn-on.

1. Layout

2. Power supply by-passing

3. Mismatch of driver to the driven IGBT

LAYOUT

A very crucial point is proper grounding. A very low-impedance path for current return to

ground avoiding loops is a good design practice. The three paths for returning current to ground

are between:

1. Driver and the logic driving it

2. Driver and its own power supply

3. Driver and the source/emitter of the IGBT being driven

All these paths should be very short in length to reduce inductance. Also, these paths should be

as wide as possible to reduce resistance. In addition, these ground paths need to be kept separate

to avoid returning ground current from the load to affect the logic line. It is very important to

note that all ground points in the circuit should return to the same physical point to avoid

generating differential ground potentials.


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POWER SUPPLY BY PASSING

Since turning an IGBT/MOSFET on and off amounts to charging and discharging large

capacitive loads, the peak charge current need to be within the capability of drive circuit. At the

same time the driver will have to draw this current from its power supply in a short period of

time. This means that using of proper by-pass capacitors for the power supply becomes veryimportant. A pair of by-pass capacitors of at least 10 times the load capacitance with

complementary impedance, used in parallel and very close to the VCC pin, can take care of this

issue. These by-pass capacitors should have the lowest possible equivalent series resistance

(ESR) and equivalent series inductance (ESL) and the capacitor lead lengths should be as short

as possible.

MISMATCH OF DRIVER TO IGBT

Since all IGBT/MOSFET driver ICs have some losses, it is necessary to calculate the power

dissipated in the driver for a worst-case condition. The total power dissipated in the Sinceambient temperature in the vicinity of the IGBT/MOSFET driver will have an effect on the

actual power dissipation capability of the driver, the maximum allowable power dissipation at

this temperature will need to be derated accordingly (in comparison to room temperature). The

selected IGBT/MOSFET driver can only be used if the maximum allowable power dissipation at

this temperature is within the capability of this IGBT/MOSFET driver.

GALVONIC ISOLATION BY OPTOCOUPLER:-

For driving high side MOSFET/IGBT in any topology, opto-couplers can be used with

following advantages:

1. They can be used to give a very high isolation voltage; 2500 to 5000 Volts of isolation is

achievable by use of properly certified opto-couplers.

2. Signals from DC to several MHz can be handled by opto-couplers.

3. They can be easily interfaced to

Microcomputers, DSPs or other controller ICs or any PWM IC.

One disadvantage is that the opto-coupler adds its own propagation delay. Another disadvantageof using an opto-coupler is that separate isolated power supply is required to feed the output side

of the opto-coupler and the driver connected to it. However, isolated DC-to-DC Converters with

few thousand Volts of isolation are readily available. This is to guarantee identical propagation

delays for all signals so that their arrival time at the gate of IGBT bears the same phase

relationships with one another as when they originated in the DSP.

GALVONIC ISOLATION BY TRANSFORMER:-

Using transformers to achieve galvanic isolation is a frequently used technique. Depending on

the range of frequencies being handled and power rating (voltage and current ratings and ratios),transformers can be designed to be quite efficient. The gate drive transformer carries very small

average power but delivers high peak currents at turn-on and turn-off of MOSFET/IGBT.


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While designing or choosing a Gate Drive transformer, the following points should be kept in

mind:

1. Average power being handled by the transformer should be used as a design guideline.

Margin of safety should be taken into account, keeping in mind maximum volt-second product

and allowing for worst-case transients with maximum duty ratio and maximum input voltage

possible.

2. Employing bifilar winding techniques to eliminate any net DC current in any winding. This is

to avoid saturation.

3. If operation in any one quadrant of B-H loop is chosen, care should be taken for resetting the

core. Advantages of employing transformers for Gate

The disadvantages of using transformers for Gate Drive are:

1. They can be used only for time varying signals.

2. It is difficult to implement DESAT protection feature.

3.3 Feature of Isolated IGBT Gate Driver:-

1. under voltage and over voltage lockout protection for Vcc.

2. dV/dt immunity of greater than 50 V/ns

3. Galvanic isolation of 1200 Volts (or greater) between low side and high side

4. On-chip negative gate-drive supply to ensure MOSFET/IGBT turn-off even in electrically

noisy environments

5. CMOS/HCMOS compatible inputs with hysteresis

6. < 20 ns rise and fall times with 1000 pf load and


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4. FUNCTIONS OF GATE DRIVERS

Floating power supply

Level shifter with appropriate isolation

Over current protection by Vce sat monitoring

Short circuit status of power circuit

Under voltage lockout

Active clamping

4.1 FLOATING POWER SUPPLY

Triggering of an inverter leg by isolated drivers

Power converters employing bridge configurations function by virtue of a high side switch, Inorder to drive a device like an IGBT or power MOSFET into conduction, the gate terminal must

be made positive with respect to its source or emitter.It can be noted that the emitter terminal of

IGBT1, in the circuit above, can be floating anywhere from ground up to the DC bus potential,

depending on the operating states of IGBT1 and IGBT2, and is therefore not referenced to the

system ground potential. A supply is therefore needed in order to provide power to any circuitry

associated with this floating midpoint potential. This type of supply is commonly referred to as a

floating supply.


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4.2 Isolated Supply

The simplest way of generating a floating supply is to uses transformer isolated supply.

Compared to other methods, this type of supply is able to supply a continuous, large amount of

current. A mains frequency transformer supply is cheap, but is usually very bulky. By

employing a high frequency isolated DCDC converter, fed from an existing DC supply, an

isolated floating supply can be generated employing a much smaller isolation transformer.

This results in excessive semiconductor power dissipation.

Optical Level shifting using optocouplers

Optical isolation using opto-couplers is another technique used for achieving level shifting. The

trade-off however, is that a separate floating supply is now required on the receiver end of the

gate driver interface. Optocouplers are suitable for isolation up to 2 KV because of the limited

distance within an IC. The following are the advantages of an optocoupler

Cost effective

Small footprint

Output enable pin available

Compatible with any logic design sine input is current driven

Commercially available opto-couplers cover a wide range of operating speeds of up to 15MBd,

with rise and fall times of 1020 ns and noise immunity levels (dv/dt rating) of 1015V/ns.

Typical opto-coupler isolation voltages are in the region of 2 kV.

Following are the disadvantages of using an optocoupler

Highly prone to noise disturbances which are inherent in driver circuit.

Separate floating supply required

Prone to ageing effect, i.e. degradation of the isolation with in

Some optocouplers have the inherent problem of drop as illustrated in the figure below. PCB layout for an optocoupler based system should be carefully designed to eliminate any

noise due to curves.


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Illustrations of inherent positive voltage drop

4.3Optical Level Shifting by Fibre Optic Link

Fibre optic cable with a transmitter and a receiver

Electrical conductors are susceptible to electromagnetic fields, and hence will radiate and

pick up electromagnetic noise. Fibre optic links neither emit, nor receive electromagnetic noise,and pass through noisy environments unaffected. In addition, when dealing with very rapidly

changing currents, ground noise can become a problem. A fiber optic link practically eliminates

any ground loop or common-mode noise problems. A basic fiber optic communication system is

given in the Fig. below

Fibre optic used for gate triggering

The LED is driven by the PWM drive signal. The light emitted from the LED is sent down a

length of fiber optic cable to the receiver. The receiver consists of a PIN photodiode and a trans-

impedance amplifier. The output voltage of the amplifier is level detected by a comparator, and

converted into a logic signal. The galvanic isolation and dv/dt rating of this communication link

can be increased to almost any desired value by simply lengthening the fiber optic cable. For a

modest length of 10 cm of fiber optic cable, the isolation voltage is approximately 100 kV. The

dv/dt rating is difficult to calculate, but as the coupling capacitance is practically zero, even the

highest realizable dv/dt rating will have little effect. The bandwidth available in fiber optics

systems makes operation at over 1GHz possible.


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5 DESIGN

5.1 Gate resistance design

Will be selected such that the maximum peak output current rating of the gatedriver optocoupler ( (peak)) is not exceeded.

IGBT gate capacitances

= + , input capacitance = , Reverse transfer = + , Output capacitance


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/ = 1/ /

/ = 1

/

/

/ = / /

= +

= +

=

Following points are considered when is to be designed

Switching time i.e. turn on and turn off time is dependent on therefore greater the greater is the switching loss.

greater the smaller is the surge voltage during switching

greater the more unlikely the occurrence of dv/dt shoot through becomes

cannot be a very small value because of EMI that is produced so there should be anoptimization


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5.2 Protection Circuit Design

In this circuit, a high voltage fast recovery diode (D1) is connected to the IGBTs collector to

monitor the collector to emitter voltage. When the IGBT is in the off state, D1 is reverse biased

and the (+) input of the comparator is pulled up to the positive gate drive power supply which is

normally +15V. When the IGBT turns on, the comparators (+) input is pulled down by D1 to the

IGBTs VCE (sat). The (-) input of the comparator is supplied with a fixed voltage (V trip)

which is typically set at about 8V. During normal switching the comparators output will be high

when the IGBT is off and low when the IGBT is on. If the IGBT turns on into a short circuit, the

high current will cause the collector-emitter voltage to rise above V trip even though the gate of

the IGBT is being driven on. This abnormal presence of high VCE when the IGBT is supposed

to be on is often called desaturation. Desaturation can be detected by a logical AND of the

drivers input signal and the comparator output. When the output of the AND goes high a short

circuit is indicated. The output of the AND is used to command the IGBT to shut down in order

to protect it from the short circuit. A delay (trip) must be provided after the comparator output to

allow for the normal turn on time of the IGBT. The trip delay is set so that the IGBTs Vce has

enough time to fall below V trip during normal turn on switching. If trip is set too short,erroneous desaturation detection will occur. The maximum trip delay is limited by the IGBTs

short circuit withstanding capability.


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Protection Circuit

and should be designed judiciously.

& is designed by considering two factors

Maximum output current that the LM311 can sink The voltage at the node between the two resistors ( 1) should be less than or equal to -6 the turn

of voltage of IGBT

Maximum base current of TIP 141/146 should be limited to less than 500mA.

Therefore is taken as 560 ohms.

1

+

+ =600

From the above two equations is found out to be 40 ohms.


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Design of & As discussed above there should be a delay circuit which is to be integrated after the sensing

stage. The delay should be such that it should be sufficient for the response of LM311 and

should not be more than the short circuit capability of the switch.

Here as an optimal choice the delay was limited to 10 us

Therefore

= 10

is taken as 10K and automatically becomes 1nF.

Typical output characteristics of SKM400B12T4 IGBT

From the characteristics above one can clearly understand how a Vce sat protection has to

be designed for the specific IGBT that has to be used


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5.3 Optocoupler triggering circuit design

Optocoupler based triggering circuit

The main parameter which has to be designed here is the input resistance. The resistance isdesigned according to the maximum input current. Obtained from the datasheet of HP 3120as

25mA.

= .

= 150Considering a small FOS the resistance,

= 270

5.5 Optical fibre Trigger circuit design


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Fibre optic circuit diagramDesign of

From datasheet the maximum forward input current of QFBR 1478 is 15mA.

Now with an input pulse voltage of 15V the input resistance should be

=

= 5 1.215

=Design of

From datasheet the maximum output current of QFBR 2478 is about 200mA.

+ =

+ = 18200

+ = 18200

+ =100 (min) + = 3


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6. CT CONCEPT CORE based driver circuit design

The new low-cost SCALE-2 dual-driver core 2SC0435T combines unrivalled

compactness with broad applicability. The driver was designed for universal applications

requiring high reliability. The 2SC0435T drives all usual high-power IGBT modules up to

1700V. The embedded paralleling capability allows easy inverter design covering higher power

ratings. Multi-level topologies are also supported.

The 2SC0435T is a driver core equipped with CONCEPTs latest SCALE-2 chipset.

The SCALE-2 chipset is a set of application-specific integrated circuits (ASICs) that cover the

main range of functions needed to design intelligent gate drivers. The SCALE-2 driver chipset

is a further development of the proven SCALE technology

The 2SC0435T targets medium-power, dual-channel IGBT and MOSFET applications.

The driver supports switching up to 100 kHz at best-in-class efficiency. The 2SC0435T

comprises a complete dual-channel IGBT driver core, fully equipped with an isolated DC/DC

converter; short-circuit protection, advanced active clamping and supply-voltage monitoring.

SCALE-2

Next Generation of Highly Integrated IGBT Gate Drivers

With the SCALE-2 chipset, CONCEPT introduces its next-generation technology platform for

scalable IGBT gate drivers introducing major advances in dynamic performance, accuracy,

functionality, flexibility and time-to-market.

The design fully employs the methodology of the CONCEPT SCALE drivers that are used in

large item numbers and have been tried and tested within a great diversity of applications.

The embedded paralleling capability allows easy inverter design covering higher power

ratings. The combination of state-of-the-art analog capabilities with moderate digital feature size

yields an optimum cost-performance ratio.

SCALE-2 driver cores

SCALE-2 driver cores are modules equipped with all the basic functions of a driver such as

electrical separation, protective functions, DC/DC converters etc. They are mounted on a circuit

board containing all the additional components required to match the driver to specific IGBTs or

applications, such as an input interface, gate resistors, active clamping etc. Driver cores for

IGBTs are available with reverse voltages from 600V to 1700V. They are also suited for driving

power MOSFETs.


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What's a Driver Core?

Driver cores are modules equipped with all the basic functions of a driver such as electrical

separation, protective functions, DC/DC converters etc.

They are mounted on a circuit board containing all the additional components required to match

the driver to specific IGBTs or applications, such as an input interface, gate resistors, active

clamping etc. Driver cores for IGBTs are available with reverse voltages from 600V to 3300V.

The 2SC0435T targets medium-power, dual-channel IGBT and MOSFET applications. The

driver supports switching up to 100 kHz at best-in-class efficiency. The 2SC0435T comprises a

complete dual-channel IGBT driver core, fully equipped with an isolated DC/DC converter;

short-circuit protection, advanced active clamping and supply-voltage monitoring.

Primary Side

1. VDC DC/DC converter supply

2. SO1 Status output channel 1; normally high-impedance, pulled down to low on fault

3. SO2 Status output channel 2; normally high-impedance, pulled down to low on fault

4. MOD Mode selection (direct/half-bridge mode)

5. TB Set blocking time

6. VCC Supply voltage; 15V supply for primary side

7. GND Ground

8. INA Signal input A; non-inverting input relative to GND

9. INB Signal input B; non-inverting input relative to GND10.GND Ground

Secondary Sides

11.ACL1 Active clamping feedback channel 1; leave open if not used

12.VCE1 VC E sense channel 1; connect to IGBT collector through resistor network

13.REF1 Set VC E detection threshold channel 1; resistor to VE1

14.COM1 Secondary side ground channel 1

15.VE1 Emitter channel 1; connect to (auxiliary) emitter of power switch16.VISO1 DC/DC output channel 1

17.GH1 Gate high channel 1; pulls gate high through turn-on resistor

18.GL1 Gate low channel 1; pulls gate low through turn-off resistor

19.Free

20.Free

21.Free

22.ACL2 Active clamping feedback channel 2; leave open if not used

23.VCE2 VC E sense channel 2; connect to IGBT collector through resistor network

24.REF2 Set VC E detection threshold channel 2; resistor to VE2

25.COM2 Secondary side ground channel 2

26.VE2 Emitter channel 2; connect to (auxiliary) emitter of power switch


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27.VISO2 DC/DC output channel 2

28.GH2 Gate high channel 2; pulls gate high through turn-on resistor

29.GL2 Gate low channel 2; pulls gate low through turn-off resistor

Description of Primary Side Interface

VDC terminal

The driver has one VDC terminal on the interface connector to supply the DC-DC converters

for the secondary sides. VDC should be supplied with 15V. It is recommended to connect the

VCC and VDC terminals to a common +15V power supply. In this case the driver limits the

inrush current at start up and no external current limitation of the voltage source for VDC is

needed.

MOD (mode selection)

The MOD input allows the operating mode to be selected with a resistor connected to GND.

Direct mode

If the MOD input is connected to GND, direct mode is selected. In this mode, there is no

interdependence between the two channels. Input INA directly influences channel 1 while INB

influences channel 2. High level at an input (INA or INB) always results in turn-on of the

corresponding IGBT. In a half-bridge topology, this mode should be selected only when the

dead times are generated by the control circuitry so that each IGBT receives its own drivesignal.

Half-bridge mode

If the MOD input is connected to GND with a resistor 71k


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Signals in half bridge mode

INA, INB (channel drive inputs, e.g. PWM)

INA and INB are basically drive inputs, but their function depends on the MOD input (see

above). They safely recognize signals in the whole logic-level range between 3.3V and 15V.

Both input terminals feature Schmitt- trigger characteristics. An input transition is triggered at

any edge of an incoming signal at INA or INB.

SO1, SO2 (status outputs)

The outputs SOx have open-drain transistors. When no fault condition is detected, the outputshave high impedance. An internal current source of 500A pulls the SOx outputs to a voltage

of about 4V when leaved open. When a fault condition (primary side supply under voltage,

secondary side supply under voltage, IGBT short-circuits or over current) is detected, the

corresponding status output SOx goes to low (connected to GND). The diodes D1 and D2 must

be schottky diodes and must only be used when using 3.3V logic. For 5V15V logic, they can

be omitted.

How the status information is processed

a) A fault on the secondary side (detection of short-circuit of IGBT module or supplyunder voltage) is transmitted to the corresponding SOx output immediately.

b) A supply under voltage on the primary side is indicated to both SOx outputs at the same

time. Both SOx outputs are automatically reset when the under voltage on the primary

side disappear.

Reference terminal (REFx)

The reference terminal REFx allows the threshold to be set for short-circuits and/or over

current protection with a resistor placed between REFx and VEx. A constant current of 150A

is provided at pin REFx.


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Collector sense (VCEx)

The collector sense must be connected to the IGBT collector or MOSFET drain with the circuit

shown in order to detect an IGBT or MOSFET over current or short-circuit.

It is recommended to dimension the resistor value of Rvc ex in order to get a current ofabout 0.6-1mA flowing through Rvc ex (e.g. 1.2-1.8M for VD C -LI NK =1200V). It is

possible to use a high-voltage resistor as well as series connected resistor. In any case, the min.

creep age distance related to the application should be considered.

Active clamping (ACLx)

Active clamping is a technique designed to partially turn on the power semiconductor as soon

as the collector- emitter (drain-source) voltage exceeds a predefined threshold. The power

semiconductor is then kept in linear operation.

Basic active clamping topologies implement a single feedback path from the IGBTs collector

through transient voltage suppressor devices (TVS) to the IGBT gate. The 2SC0435T supports

CONCEPTs advanced active clamping, where the feedback is also provided to the drivers

secondary side at pin ACLx: as soon as the voltage on the right side of the 20 resistor exceeds

about 1.3V, the turn-off MOSFET is progressively switched off in order to improve the

effectiveness of the active clamping and to reduce the losses in the TVS. The turn-off

MOSFET is completely off when the voltage on the right side of the 20 resistors approaches

20V (measured to COMx).

Active clamping

Gate turn-on (GHx ) and turn-off (GLx) terminals

These terminals allow the turn-on (GHx) and turn-off (GLx) gate resistors to be connected to

the gate of power semiconductor. The GHx and GLx pins are available as separated terminals

in order to set the turn-on and turn-off resistors independently without the use of an additionaldiode. Please refer to the driver datasheet for the limit values of the gate resistors used.


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Power supply and electrical isolation

The driver is equipped with a DC/DC converter to provide an electrically insulated power

supply to the gate driver circuitry. All transformers (DC/DC and signal transformers) feature

safe isolation to EN 50178, protection class II between primary side and either secondary side.

Note that the driver requires a stabilized supply voltage.

Power-supply monitoring

The drivers primary side as well as both secondary-side driver channels is equipped with a

local under voltage monitoring circuit. In the event of a primary-side supply under voltage, the

power semiconductors are driven with a negative gate voltage to keep them in the off-state (the

driver is blocked) and the fault is transmitted to both outputs SO1 and SO2 until the fault

disappears. In case of a secondary-side supply under voltage, the corresponding power

semiconductor is driven with a negative gate voltage to keep it in the off-state


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7. RESULTS AND OBSERVATIONS

Gate driver circuit has been basically divided into two sections one is the power supply section

and the other is the signal transmission section.

7.1Opto - Based gate driver7.1.1 Floating Power supply (+15,-15)

Power supply (+15,-15)

Features:

Supplies two floating power supplies each of Vcc+15V to Vee-15V

Transformer specially designed for high frequency and made of ferrite core

As mentioned before because of the inherent drop within the optocoupler, the transformer turns

has to be changed and corresponding changed has to be made in the circuit.


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7.1.2 Floating Power supply (+17,-7)

Power supply circuit for +17,-7

7.2 Optocoupler based triggering circuit


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7.3 Optical fibre based triggering circuit

Schematic diagram of optical fibre triggering circuit

Protection and Driver circuit

Schematic of protection circuit


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Features:

It crosses a prescribed value the gate pulse is made low. Vce sat protection for over current.

Here the IGBT Vce sat will be monitored continuously and whenever it

7.5 CT CONCEPT CORE based IGBT DRIVER


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7.6 Output Waveforms:

WITHOUT PROTECTION

Collector-emitter rise time

Without protection collector-emitter fall time

Gate pulse turn off


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Gate turn on

Capacitor C12 charging

Capacitor discharging


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WITH PROTECTION

Capacitor voltage

Collector emitter voltage

Collector-emitter and capacitor voltages


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7.7 Vce SAT Protection (short circuit) Testing

Circuit for testing of protection circuit

PROCEDURE:

At first make the test set up with the number of diode as shown

Make the connection from the collector to the capacitor C12 by shifting between the diodes

Note the point in which the protection inherent in the circuit starts to function.

Adjust the protection as a function of the maximum current to be flown through the IGBT.

INFERENCES:

Positive peak of gate pulse 15V

Negative peak of gate pulse -5V

Turn on time 1us

Turn off time 1us

Protection response time 2.5us


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8. Experimental setups

Opto coupler Based IGBT driver


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Optical fibre based IGBT driver

CT CONCEPT core based IGBT driver


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Conclusion

Integrated power electronic solutions have become the current trend for applications with the

development of Smart Power modules. These modules contain the entire inverter semiconductor

stack as well as fully integrated gate drive circuitry. Driver circuit is now an integral part of

every high power converter, weather it is AC to DC or DC to AC or DC to DC or AC to AC. It

is now been used as a protection for both the logic circuitry and the switch were earlier it was

used only for the protection of the logic circuitry. The main functions of the Driver circuit being

as a current buffer and isolation has taken into consideration when the reliability issue comes

into picture. Now a days more features have been incorporated in driver circuitry for protection.

Due to its enhanced features the driver circuit is now days acknowledged as intelligent drives.

Gate drive circuits are a crucial part of design. Gate drive transformers add a level of

ruggedness to your design that cannot be achieved with silicon solutions. Additional active

elements to supposedly speed up the device switching do not usually offer improvements inoverall performance, but they do introduce new potential failure mechanisms.


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APPENDICES

PCB LAYOUTS

Optical fibre based IGBT driver

Optocoupler based IGBT driver


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DATASHEETS

OPTOCOUPLER


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OPTICAL FIBRE

Transmitters


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SEMIKRON IGBT


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CT concept core


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REFERENCES

1. D. R. H. Carter, Aspects of High Frequency Half-Bridge Circuits,PhD Thesis,

Cambridge University, September 1996.

2. N. Mohan, T. Undeland, and W. Robbins, Power Electronics: Converters, Applications andDesign, Wiley, Brisbane, 1989.

3. S. Clement and A. Dubhashi, HV Floating MOS-Gate Driver IC,Integrated circuit

designers manual.

4. Application Note, Hints and Applications Design manual,Chapter 3, Semikron Corporation.

5. M. Munzer, W. Ademmer, B. Strazalkowski, and K. T. Kaschani, Coreless Transformer a

New Technology for Half Bridge Driver ICs, application note, 2005, www.eupec.com.

6. I. de Vries, High Power and High Frequency Class-DE Inverters, PhD Thesis, Departmentof Electrical Engineering, University of Cape Town, August 1999.

7. Application Note AN-937, Gate Drive Characteristics and Requirements for HEXFET

Power MOSFETs, www.irf.com.

8. Data sheet, SKHI22, www.semikron.com.

9. Application Note 30, Matching MOSFET drivers to MOSFETs, TelCom Semiconductor

Inc.

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