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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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