Device Physics I

Summary

This lecture delves into advanced power electronics, focusing on device physics, particularly power diodes and thyristors. It discusses the evolution and capabilities of power diodes, highlighting their higher voltage blocking and conduction losses compared to conventional diodes. The lecture also touches on semi-controlled devices like thyristors, which can be turned on but not off, and their significance in power electronics since their invention in 1956. The discussion sets the stage for upcoming classes on thyristors, GTOs, and other power electronics devices.

Takeaways

• 📚 The lecture series focuses on advanced power electronics control, with the third lecture dedicated to device physics, specifically discussing SCS and power diodes.
• 🔌 Power diodes are designed to handle significantly higher power levels compared to conventional diodes, with capabilities 1000 to 10^6 times higher.
• 🌐 The power diode's n-drift region is crucial for its high reverse blocking capability, which results in a higher forward voltage drop compared to standard diodes.
• ⚡ The diode's forward characteristics are similar to those of a standard diode, but the forward voltage is generally higher due to the increased blocking capability.
• 🔄 Diodes are uncontrolled devices with reverse blocking and forward conduction capabilities, making them suitable for applications like rectifiers.
• 📉 The dynamic characteristics of diodes, including turn-on loss and reverse recovery time (trr), are essential for understanding their performance in circuits.
• 💡 Schottky diodes offer extremely fast recovery times and low forward voltage drops, making them ideal for low output voltage circuits and high-frequency applications.
• 🌐 The script introduces various diode types, including fast recovery diodes, which are crucial for high-frequency applications due to their quick trr.
• 📈 The lecture also touches on the history and development of power electronics devices, emphasizing the significance of the thyristor's invention in 1956.
• 🔄 Thyristors are semi-controlled devices with the ability to control the turn-on but not the turn-off, leading to extensive research on commutation techniques.

Q & A

What is the main focus of the third lecture on advanced power electronics control?

The main focus of the third lecture is on device physics, specifically discussing the characteristics and applications of power diodes and thyristors.

What is the difference between a conventional diode and a power diode?

A power diode has a much higher power handling capability, at least 1000 times higher or even 10 to the power 6 times higher than a conventional diode. It also has a higher forward voltage drop due to its larger drift region, which provides a higher reverse blocking capability.

Why is the forward voltage drop of a power diode higher than that of a conventional diode?

The forward voltage drop of a power diode is higher due to the presence of a drift region, which is designed to handle higher voltages and current loads, resulting in higher conduction losses.

What is a thyristor and how does it differ from a diode?

A thyristor is a semi-controlled device that combines two PN junctions in series, unlike a diode which is a single PN junction. It can be turned on by a signal but cannot be turned off by a signal; it requires an external commutation process to turn it off.

What is the significance of the reverse recovery time (trr) in diodes?

The reverse recovery time (trr) is a critical parameter that affects the diode's performance in switching applications. A shorter trr is necessary for high-frequency applications to minimize switching losses and electromagnetic interference (EMI).

Why are Schottky diodes preferred in low output voltage circuits?

Schottky diodes are preferred in low output voltage circuits because they have a lower forward voltage drop, typically around 0.3 volts, which reduces power loss and increases efficiency.

What are the typical applications for ultrafast diodes with a reverse recovery time (trr) in the nanosecond range?

Ultrafast diodes with a reverse recovery time (trr) in the nanosecond range are typically used in high-frequency applications such as switch-mode power supplies (SMPS) where fast switching is required.

How does the leakage current of a power diode compare to that of a low signal diode?

The leakage current of a power diode is generally higher than that of a low signal diode due to the larger drift region and the higher doping levels required for blocking higher voltages.

What is the role of the n-drift region in a power diode?

The n-drift region in a power diode is designed to absorb the depletion layers and provide a higher reverse blocking capability. It also contributes to the higher forward voltage drop when the diode is forward biased.

Why are thyristors considered semi-controlled devices in power electronics?

Thyristors are considered semi-controlled devices because they allow control over the turn-on process but do not provide a means to control the turn-off process, which necessitates external commutation techniques.

Outlines

00:00

🔬 Introduction to Power Electronics Devices

The lecture delves into the world of advanced power electronics control, focusing on device physics. It introduces various power handling devices such as the power diode, which has a significantly higher power handling capability compared to conventional diodes. The lecture also covers the unique features of thyristors, which are semi-controlled devices allowing for turn-on control but not turn-off. The discussion extends to bidirectional thyristors, TRIACs, and GTOs, which offer different levels of control and power handling. The evolution of power devices is traced from BJTs to power MOSFETs, highlighting the advancements in power handling and efficiency. Modern devices like IGBTs, which combine the benefits of BJTs and MOSFETs, are introduced, along with the emergence of silicon carbide-based devices for high bandwidth applications. The lecture sets the stage for a detailed exploration of power diodes, their construction, and their unique characteristics compared to standard diodes.

05:04

📚 Detailed Explanation of Power Diodes

This section provides an in-depth look at power diodes, emphasizing their ability to block high voltages and their construction, which includes an extended n-drift region for enhanced reverse blocking capability. The lecture explains the forward and reverse characteristics of power diodes, noting that the forward voltage drop is higher than that of standard diodes due to the drift region. It discusses the importance of the drift region's thickness in determining the diode's reverse breakdown voltage and how it affects conduction loss. The summary also touches on the symbol representation of diodes and their applications in power electronics, particularly in rectifier operations where they are chosen based on their reverse breakdown voltage to handle peak inverse voltages from three-phase systems.

10:05

🔌 Dynamic Characteristics and Types of Diodes

The paragraph discusses the dynamic characteristics of diodes, focusing on the rate of change of forward voltage and current, which is crucial for understanding diode behavior under varying conditions. It explains the concept of turn-on loss due to the junction capacitance and the time it takes for the current to reach its rated value after the voltage is applied. The lecture also covers the reverse recovery process, detailing the time it takes for the diode to regain its reverse blocking capability after the current drops to zero. Key terms like trr (reverse recovery time), IRR (maximum reverse current), ta, and tb are introduced, providing a framework for understanding diode performance in different applications. The discussion differentiates between fast and slow diodes, with fast diodes being suitable for high-frequency applications due to their quick recovery times and slow diodes being more appropriate for lower frequency operations where soft recovery is acceptable.

15:07

💡 Applications and Specifications of Power Diodes

This section delves into the practical applications and specifications of power diodes, highlighting their use in different power electronics scenarios. It discusses the importance of choosing the right diode based on the frequency of operation, with fast diodes being preferred for high-frequency applications like SMPS and slow diodes for lower frequency rectification. The lecture provides insights into the data sheets of power diodes, explaining parameters such as current-carrying capability, surge current capability, power dissipation, thermal resistance, and operating temperature ranges. It also covers the significance of reverse recovery time (trr) and how it varies with different diode types, affecting their suitability for specific applications. The summary provides a comprehensive overview of how diodes are selected and used in power electronics, emphasizing the balance between performance, cost, and reliability.

20:09

🌐 Transition to Controlled Power Devices

The lecture concludes with a transition from uncontrolled and semi-controlled devices like diodes and thyristors to fully controlled devices. It discusses the limitations of diodes, which can only block reverse voltage and allow forward current flow, and the need for devices that can actively control both on and off states. The paragraph introduces thyristors as semi-controlled devices that can be turned on by external signals but turn off only through natural commutation or forced commutation techniques. The historical context of the thyristor's invention in Bell Laboratories and its impact on the power electronics industry is provided, highlighting its high power handling capability and efficiency. The lecture sets the stage for further discussions on thyristors, GTOs, and other controlled devices in subsequent classes, promising a deeper dive into their characteristics and applications.

Keywords

💡Power Diode

A power diode is a semiconductor device designed to handle high voltage and current, unlike the standard diodes used in analog electronics. It is characterized by its ability to block high voltages in the reverse direction while allowing current to flow in the forward direction. In the script, the power diode is highlighted for its significantly higher power handling capability, which is at least 1000 times higher than conventional diodes, making it crucial for high-power applications in power electronics.

💡Thyristor

The thyristor, also known as a silicon-controlled rectifier (SCR), is a four-layer, three-junction semiconductor device that can be thought of as two diodes connected anti-parallel. It is a semi-controlled device because it allows control over its turn-on but not its turn-off. The script discusses the unique feature of thyristors, which is their ability to be turned on by a signal but their inability to be turned off without external commutation, making them a key component in many power electronics applications.

💡TRIAC

A TRIAC, or triode alternating-current switch, is formed by two anti-parallel thyristors in the same package, allowing it to control alternating current (AC). The script mentions that the power handling capability of TRIACs is relatively low compared to other devices, and they are being phased out with the advent of matrix converters, indicating a shift in technology within power electronics.

💡GTO

A Gate Turn-Off (GTO) thyristor is a special type of thyristor that can be turned off by a negative gate current, overcoming the limitation of standard thyristors that cannot be turned off without external commutation. The script emphasizes the importance of GTOs in applications where the ability to turn off current flow is necessary, showcasing an advancement in power electronics device technology.

💡BJT

Bipolar Junction Transistor (BJT) is a type of transistor that allows current flow in both directions. The script refers to power BJTs, which are designed to handle higher power levels compared to their analog counterparts. However, they have a short lifespan due to high gate current requirements, and their usage has declined in favor of power MOSFETs.

💡Power MOSFET

A Power MOSFET, or Metal-Oxide-Semiconductor Field-Effect Transistor, is a type of transistor used for switching applications in power electronics. It is valued for its high input impedance and low output impedance, which makes it suitable for high-power applications. The script notes that power MOSFETs have power handling capabilities in the kilowatt range, indicating their importance in modern power electronics.

💡IGBT

An Insulated Gate Bipolar Transistor (IGBT) is a three-terminal power semiconductor device that combines the attributes of both MOSFETs and BJTs. The script highlights the IGBT's unique features, such as low gate drive requirements and high current handling capabilities, which have revolutionized power electronics by offering a balance between efficiency and controllability.

💡SIC

Silicon Carbide (SIC) refers to semiconductor devices made from silicon carbide, a material known for its superior thermal conductivity and ability to operate at higher temperatures and voltages than silicon. The script mentions SIC as part of the advancement over IGBTs, indicating a move towards materials that can further enhance the performance and efficiency of power electronic devices.

💡Reverse Recovery Time (trr)

The reverse recovery time (trr) is a critical parameter for diodes, especially in high-frequency applications. It refers to the time it takes for a diode to recover from a forward conduction state to a reverse blocking state. The script discusses the importance of trr in selecting diodes for specific applications, with faster recovery times being necessary for high-frequency operations and slower times being acceptable for lower frequency applications.

💡Schottky Diode

A Schottky diode is a type of semiconductor diode that has a low forward voltage drop and very fast switching capabilities. The script contrasts Schottky diodes with power diodes, noting their lower reverse blocking capability but faster recovery times, making them suitable for low output voltage circuits and high-frequency applications.

Highlights

Introduction to advanced power electronics control with a focus on device physics.

Discussion on power diodes with a power handling capability 1000 to 10^6 times higher than conventional diodes.

Explanation of the unique features of thyristors, including their semi-controlled nature with controllable turn-on but uncontrollable turn-off.

Introduction to bidirectional thyristors and their evolution into TRIACs, with a note on their phasing out due to the advent of matrix converters.

Discussion on GTOs (Gate Turn-Off thyristors) as a solution for thyristors' lack of turn-off capability.

Overview of power BJTs, their limitations, and the shift towards power MOSFETs for higher power handling.

Introduction to IGBTs, their discovery, and their significance in combining the utilities of BJT and MOSFETs.

Mention of modern devices like SIC, TH, MCT, IGCT, and COOLMOS, indicating advancements over IGBTs.

Detailed explanation of power diodes, their structure, and the importance of the drift region in determining reverse breakdown voltage.

Discussion on the forward and reverse characteristics of power diodes, including their ideal and switching characteristics.

Explanation of dynamic characteristics of diodes, including turn-on loss, reverse recovery voltage, and reverse recovery time (trr).

Differentiation between fast and slow diodes based on their reverse recovery time and their applications.

Description of Schottky diodes, their low forward voltage drop, and applications in low output voltage circuits.

Overview of data sheets for power diodes, including current carrying capability, surge current capability, and thermal resistance.

Discussion on the selection of diodes for different applications based on their blocking voltage and forward voltage drop.

Introduction to semi-controlled devices like thyristors and their significance in the evolution of power electronics.

Historical context of the invention of thyristors at Bell Laboratories and their impact on high-power applications.

Transcripts

Welcome to our lectures on advance power electronics control.

Today is our third lecture, we will continue with our device physics.

That is the components we will discuss today is that SCS and power diode.

So this will be actually all the devices that is going to be covered within subsequent two

classes.

That is basically you know from the 50 years rather we are using diode.

But we will see that this is power diode that power handling capability of this diode at

least actually 1000 times higher or maybe 10 to the power 6 times higher.

So this will be called a power diode.

Thereafter, we will see that you know thyristors is a unique combination that is a 2 PN junction

diode has been connected in series and it forms unique features and thus it will be

a semi controlled device.

It turn on can be controlled but turn off cannot be controlled.

Thereafter, bidirectional thyristors when you put actually two anti-parallel thyristors

in a same package, essentially it becomes a TRIAC but power handling capability of the

TRIAC essentially is very less and nowadays it is getting almost phased out with the advent

of the matrix converter.

Thereafter, GTO since thyristor does not have a turn off capability, it require an external

procedure to turn on that is called commutations and we can turn off a kind of thyristors with

negative gate current so that will be GTO that will also be covered.

Thereafter, BJT this is also power BJT because in analog electronics we have studied BJT

but that power handling capability is quite low in watt.

It should be in a kilowatt or megawatt but it has shown a very little life span.

Nowadays, it is not been used because of the high gate current requirement and instead

of that we have a power MOSFET and also it has got a power handling in the range of the

kilowatt level.

So these are the conventional devices that we use.

Apart from that, you know we have now few modern devices that is IGBT.

IGBT is discovered by one Indian ((in GE)) (02:50) so from there actually dimension of

the power electronics changes because it combines the actual utility of the BJT and MOSFETs

and it came out with a unique feature which has a low gate dissipation and high current

handling capability.

Thereafter, SIC, TH, MCT, IGCT is one of the advancement over the IGBT and thereafter COOLMOS,

etc.

And we are also now actually reaching out for the silicon carbide-based devices or high

bandwidth devices.

Let us now talk about the power diode in details.

So difference is that you know we have this power diode has to have a block, huge amount

of voltages than the conventional diode which we have studied in the analog electronics.

For this reason, you know you will find that n layer is stretched.

It is not that only in PN junction you can find that -n and the +n.

And for ((this reason)) (03:53) drift region and thus you know what we assume for the silicon

diode that actually it will have a forward drop voltage of 0.7 volt, instead of that

it will be higher because of this actually drift region is higher and that gives the

actually higher reverse blocking capability but also it gives a higher conduction loss.

So the thickness of the n-drift region depends on the reverse breakdown voltage of the diode.

So this drift region determines the reverse breakdown voltage of the diode.

The function is to absorb the depletion layers, the reverse versus the PN junction and it

is lightly doped it will add significant ohmic resistance for this I was telling that actually

drop will be higher to the diode when it is forward biased.

For higher breakdown voltage, the drift region will be wide so this region will be wider

if required to have a higher reverse blocking voltage.

And n-drift region is absent for low signal diode which we have studied in analog electronics.

Now this is the symbol of the diode.

You are quite familiar from the analog electronics.

And you know this is the structures, this is a PN junction in between you have extra

layer that is you might have seen, this is -drift region, -n layer has been put inside

it to give you a reverse voltage blocking capability and this is basically the forward

characteristics of the diode, it is same but this voltage may not be actually 0.7, it is

generally higher depending on which amount of the blocking capability that diode have.

We refer to the data sheet then we will find out and this is basically the Avalanche breakdown

and this VBR in this power diode we generally assume to be about more than 500 volt because

it will be used for this power electronics purposes.

So mostly in a rectifier cases, so actually for the 3 phase voltage which is required

to be rectified so peak inverse voltage comings out to be around 600 volt for the 3 phase

voltages.

So accordingly we require to choose the rating of the reverse effect breakdown voltage and

this is actually the ideal characteristics of the switching characteristics.

Diode essentially is an uncontrolled device, it has reverse blocking capability which has

been shown by this line and it will conduct into the forward region, this is the mode

of operation.

It does not have forward blocking capability and the reverse current flow capability.

So it has a forward conduction capability and the reverse blocking capability.

This is the characteristics of the diode.

Anywhere you require this kind of characteristics; you can suitably place a diode instead of

any control switches.

So let us see that you know we have a different kind of diode where we will find that it is

a normal diode that will be used for the rectifier operation mainly.

Most of the power actually from AC to DC you actually use rectifications but power qualities

and issues still we use that and for this reason we have a different kind of diode and

for this we require to understand actually dynamic characteristics of the diode.

So what happened when you apply a point of voltage builder, current also builds up and

there is a rate of change of the forward voltage current and that will pick up.

So in this region you can see that the voltage is also building up, current is also building

up because it has got a junction capacitance, so current will also build up.

So in this region you know actually diode will give you a voltage drop, power drop across

this diode.

That is called the turn-on loss of the diode.

Thereafter, what happen once it reaches through the voltage then voltage will fall and ultimately

you know when voltage becomes zero to when voltage falls down to its actually forward

blocking voltage let say 0.7 or 0.8 volt or more than that depending on the amount of

the depletion layer, so this time is called t2.

By the time you know actually, current will be actually to its saturated value or whatever

the rated current it will flow.

And it will continue thereafter once you decided to actually take steps to reduce the voltage,

then definitely actually you can find essentially here current become zero but even though the

current becomes zero it does not have a reverse blocking capability because of the trap charge

into the PN junction diode and you know since there is extra substrate present, it will

take considerable more amount of time to actually drain out the charges from the trap region.

For this reason, you know actually you have to apply a reverse voltage; this is called

reverse recovery voltage VRR.

Then, actually this trap charges will come out gradually, ultimately current will flow

in the negative direction for the short duration of the time and ultimately again it will go

out and this time you know actually total time it is called the trr and it will have

a leakage.

Thereafter, after trr leakage current will flow through it and leakage current should

be actually one-fourth of this actually the maximum reverse current flows.

So it should be around 25%.

So this is the actually the characteristics of the diode.

So let us get familiar with the few terms that is trr that is reverse recovery time

measured at the time between the initial zero crossing of the diode current to the same

time.

When this current reaches 20% of the peak reverse current and that is assumed to be

basically the leakage current of the diode and IRR maximum reverse current that will

be also specified on a data sheet, will show it and you know trr is a major fundamental

parameter of the diode for different applications.

If you are using a diode for SMPS kind of applications and which is for choosing frequency

is very high and thus require very fast reverse or very small reverse recovery time.

So we have to choose a fast diode.

Similarly, diode is using for rectification operation of the 50 Hertz or 60 Hertz supply.

You can afford to take a slow device, slow diode or a snappy diode and if you require

extremely fast devices almost zero on in level of the nanoseconds then Schottky diode will

be preferred but of course higher will be the power of blocking capability.

So trap charge will be there and higher will be your value of the trr and also now your

drop conduction drop will also increase if it has a higher PIV or peak inversion voltage

and ta is a time between the zero crossing and the maximum reverse current and that is

due to the charge stored in the depletion region of the junction and tb is the time

is where actually the time reverses.

This is basically the two times ta and tb, so we have to find it out the maximum power

reverse current trr is 25% of the maximum reverse current and IRR is due to the charge

stored in depletion region or bulk semiconductor material.

So let us see, so this much is ta and this much is tb and if this recovery is this kind

of thing, it takes actually considerable amount of time, then we call it is soft recovery

and stress across this diode is less and diode will have a less conduction loss also, so

but you will have a higher value of trr but if you want actually very fast recovery for

high frequency applications then what happened you know tb is considerably low.

Ratio of ta and tb is basically one of the measurement of the diode's promptness but

problem lies, there is a two problem if you require to have a fast higher recovery voltage,

you cannot do anything, you require to choose this kind of diode.

It will have a high EMI, EMC problem as well as you know actually cost of the diode definitely

will be more.

Apart from that actually the stress across this diode also will be higher.

So we have another diode that is called Schottky diode which has extremely low or almost zero

turn off time.

Reverse blocking capability is extremely low compared to the power diodes.

So these diodes are used where low forward voltage drop usually 0.3 volt is needed in

low output voltage circuit.

So these diodes are limited to their blocking capabilities of the voltage in the range of

50 to 100 volt whereas actually you will find that power diode can easily block 1000 volts.

As compared to the PN junction diode, it has lower cut in a voltage, higher reverse leakage

current that is we guess you know they will find that leakage current will be little higher

and two times higher than the normal power diode of the same rating.

Higher operating frequency, you can operate for the SMPS and other applications.

So this is one of the applications.

So this is basically the PN junction diode and this is a Schottky diode and this drop

will be instead of 0.7, it will be around 3 to 4 volt and PN junction will have a 0.7

volt and one of the advantages is that it has got a fastest recovery except SIC.

So how you will categorize fast diode and the slow diode?

So fast recovery diode actually will go from this point to this point, so basically this

is the region you know this is the current, if you integrate over time, this is the charge.

Ultimately, your depletion region should hold very less amount of charge that is the only

solution to provide a fast recovery and that is used for the high frequency application.

So if you integrate over it though this gives you the charge.

So this is used for the high frequency circuit in a combination with the controllable switch

by a small reverse recovery time is needed at power level of the several hundred volt

and several hundred amperes of diodes, trr having times less than the microsecond.

We shall see the dataset in a normal rectification operation, what kind of trr you will get it

and another is that low frequency diode.

Low frequency diode is normally used for the rectifier operations and we want actually

lower conduction loss because it can carry then higher current and drop will be lower

but it will have a soft recovery or a slow recovery.

So the on state voltage of the diode is designed to be low as possible as a consequence it

has larger trr which are acceptable for the line frequency applications in 50 hertz or

60 hertz depending on the countries you are using.

These diodes are available with a blocking voltage of ratings of the several kilovolts

and the current ratings of the several kilo amperes.

Moreover, they can be connected in series and parallel to satisfy the voltage and the

current requirement.

So this is the data sheets of one of the power diode in a nominal power rating not very high

rating.

So you can see that what are the parameter will be given, you know this is the current

carrying capability of this diode is only 1 ampere to 3 ampere and at a temperature

of the still 75 degree centigrade there is no thermal runaway or the thermal breakdown

and one aspect is that surge current capability.

Surge current capability is quite high, it is as high as 200 ampere and you know there

is power dissipation and you know this power dissipation can be as high as 6 watt, 6.25

watt and you know this is the thermal resistance and junctional operating point can be -55

to 150 degree centigrade.

Another important data is given that value of the trr, I am coming to this little you

can see that it is 1.5 microsecond.

And you know there is difference series depending on you can choose a different power rating,

you can see that this is basically the peak repetitive voltage if you apply for the rectifier

operation that is very important because you have a negative half cycle.

So it can block, it can start from actually the 50 to 1000 you can choose any diode depending

on its rating in between and so if you choose 5408, it has a blocking capability of the

1000 volt.

And maximum RMS rating will be 700 volt and reverse blocking capability will be same.

The peak voltage, peak repetitive voltage that will be 1000 volt and you can have a

maximum forward voltage at you can see that this is not actually 0.7 volt which you have

assumed in the actually analog electronics or the linear electronics diode.

It is basically 1.2 volts, so it gives you the considerable drop.

And we have a full leakage current of around 0.5 milliampere and you got a junctional capacitance

in the range of the 30 picofarad at 1 megahertz.

So now let us see a fast diode okay.

Generally, two anti-parallel diodes are connected in series so forth this is and we have this

kind of terminal.

So you can have a 4 terminal, so generally these diodes will have a series of MUR 16

thereafter some numbers, 10 is actually will have a lower blocking capability and 60 will

have a higher blocking capability.

So ultrafast diode, you have seen that you know in previous diode has a trr or reverse

recovery time in 1.5 or 1500 nanosecond, here it will have only 35 to 60 nanosecond.

Thus, it is a fast diode or fast recovery diode and find its application in SMPS or

the any application where high frequency demands.

It has got a huge operating point; it can operate as high as 175 degree centigrade.

Popular package is this one and it meets actuals this is the UL standard, UL actually the standard

is used for the European Union for anyone is exporting in a European Union, it has to

meet this security standard of UL94.

Higher temperature glass passivated junction, for this it can operate at 175 degree centigrade

and high voltage capability, it can block as high voltage as 600 volt, leakage has been

specified even as high temperature 150 degree centigrade.

Current derating both the cases of the ambient temperature has been specified and one aspect

is that now one of the standard requirements of any modern country is that it should have

a lead-free package.

You would also have a lead-free package for the environmental issues and weight is just

you can see that around 2 grams, quite light and all external surfaces corrosion free and

lead temperature of the soldering purpose and temperature while soldering can go to

the actually 260 degree centigrade for the period of 10 seconds.

No harm will be done on the diode.

So these are the few features I was talking about, as this number goes you know you can

see that power blocking capability increases.

See that we had a blocking capability of the 1000 volts but anyway since it has a very

fast recovery; it has only a power blocking capability of only 600 volt.

So for this reason while choosing a diode, you require to understand it.

What is another advantage of it?

It can handle huge current; you know it can handle 8 ampere of current or 16 ampere of

current.

Now the peak forward current is basically the 16 ampere and negative repetitive peak

surge current can be as high as 100 ampere, it was same there but operating range is quite

high, it is -65 to 175 degree centigrade.

So it is a quite suitable for high frequency application.

And apart from that you know actually we have actually other data's that is that is what

the important thing is that trr value is 35 or 25 nanoseconds depending on the forward

current and if it is 1 ampere current is flowing and di/dt is 50 ampere per microsecond then

actually you will have only 35 microsecond.

If it is 0.5, then it will have actually 25 nanoseconds and data's are almost same for

other values.

So these are basically the forward conduction voltage drop, you can see, it is just little

above 0.7 volt.

So thus it is an excellent diode, it is 0.895 and 0.975 for different junctional temperature,

higher junctional temperature will give you lower conduction loss that is the advantage

of it and this is basically the characteristics of this diode.

Now we shall get ventured into a controlled device.

But first we will go to the semi controlled device.

Problem of diode is that it can block reverse voltage and allow current to flow in forward

conduction mode but it is quite necessary for different application we required to have

forward voltage carrying capability and thus is necessitate or it is a controlled though

it is semi controlled because you cannot stop that switch but you can on it.

So for this reason, actually one device was discovered 60 years ago in 1956.

So the thyristors is called half controlled device and as turn on time can be controlled

only.

So you can control when to turn it on and it has got a forward blocking voltage capability

and we can say that power electronics era started with the invention of the thyristor.

Thus, we get into the venture into the power electronics when thyristors becomes fully

functional and we can play around thyristors in those days.

And there is many research because turning on can be controlled, turn off cannot be controlled

so how to turn off, so that was the main research in actually 60s.

Thereafter, once we come out with the different technique of turn off, then it has been applied

to the different topology apart from the controlled rectification operations and that was a domain

of 70s.

Thereafter, full controlled device due to the Baliga and all IGBT came and thus different

application we do not use thyristors anymore.

And GTO came but still considering the power handling capability, no one cannot breach

the capability of the thyristors.

Thyristors has got highest power handling capability as far as current and voltage is

concerned and also the less loss compared to the turn-on and turn-on loss compared to

any other devices as concerned.

So these are the few information we shall take it away.

It was the same lab where transistors were discovered.

It was invented in 1956 in Bell Laboratories and first came into the production after a

year in 1957, so it is almost 60 years and later after one year later the commercially

it is available and it basically replaced all the vacuum power devices.

We had a thermionic emission-based control rectification and that was removed and we

came into the era of this power electronics from that point.

And it is used in high-power application due to its high power handling capability.

We shall continue with the thyristors in our next class.

Thank you for your kind attentions.

We shall discuss thyristors in thorough and its characteristics and its applications,

thereafter we will switch over to the GTO and other devices.

Thank you so much for your attention.