Device Physics II

Summary

This lecture delves into the physics of thyristors, key components in power electronics and control. It covers the thyristor's history, structure, and operation, highlighting its role in high-power applications since the 1960s. The discussion includes the device's forward and reverse blocking capabilities, the significance of the gate for triggering, and the impact of design on switching speed. Technical specifications from data sheets are reviewed, emphasizing the importance of understanding these for practical applications, with a look ahead to modern devices like IGBT and IGCT.

Takeaways

• 📚 The lecture is part of a series on device physics and power electronics, focusing on the thyristor.
• 💡 The thyristor was commercialized in 1960 and replaced thermionic-based switches like vacuum tubes due to its high power handling capabilities.
• 🔍 Thyristors are essentially two diodes connected in series, with a PNP-NPN transistor model used for analysis.
• 🛠️ The gate of a thyristor can be used to trigger the device from a forward-blocking state to a forward-conducting mode.
• ⚠️ It's crucial not to trigger a thyristor when the cathode voltage is greater than the anode voltage, as this could damage the device.
• 🔑 The thyristor consists of a four-layer p1n1p2n2 structure, with an anode, cathode, and gate as the main terminals.
• 🌡️ High voltage thyristors use a highly resistive n-base region to support large forward voltages when in the off state.
• 🔋 The thickness of the n-base region affects the thyristor's switching speed; a thicker region provides higher voltage blocking but slower switching.
• 🔗 Thyristors have different appearances and are often mounted on heat sinks due to their high power handling capabilities.
• 📈 The characteristics of thyristors include forward blocking, gate-triggered conduction, and a specific set of switching times like delay time (td), rise time, and gate turn-on time (tgt).
• 📉 The trade-off between forward blocking voltage rating and forward voltage drop during conduction is essential for selecting the right thyristor for an application.

Q & A

What is a thyristor and when was it first commercialized?

A thyristor is a four-layer semiconductor device composed of alternating PN type materials, with three terminals: anode, cathode, and gate. It was first commercialized in the 1960s and has since replaced thermionic-based emission switches like vacuum tubes due to its high power handling capabilities.

Why is the thyristor normally off?

The thyristor is normally off because when a voltage is applied such that VA>VK (anode voltage greater than cathode voltage), junction J2 is reverse biased, allowing only a small leakage current to flow, thus blocking the forward current.

How can a thyristor be turned on?

A thyristor can be turned on by applying a voltage to the gate terminal that is sufficient to break down the junctional barrier, allowing current to flow and putting the device into forward conduction mode.

What is the significance of the n-base region in a thyristor?

The n-base region in a thyristor is a highly resistive area that provides the device with its blocking capability. It is crucial for supporting the large forward voltage when the switch is off or in the forward blocking state.

How does the thickness of the n-base region affect the thyristor's performance?

The thickness of the n-base region affects the thyristor's forward blocking voltage and switching speed. A thicker n-base region can support a higher forward blocking voltage but will result in slower turn-on and turn-off times.

What is the role of the gate in a thyristor's operation?

The gate in a thyristor serves as a control terminal. It can be used to inject a small current that, when applied, can trigger the thyristor to switch from the off state to the on state, even when the anode-cathode voltage is below the breakdown voltage.

What are the two transistor models that represent a thyristor?

A thyristor can be represented by two transistor models: a PNP transistor and an NPN transistor, which are connected in such a way that the base-emitter junction of one transistor is connected to the base-collector junction of the other.

What is the forward breakdown voltage (VBO) of a thyristor and how is it determined?

The forward breakdown voltage (VBO) of a thyristor is the voltage at which the thyristor transitions from the forward blocking state to the forward conduction state. It is typically determined through destructive testing and is specified in the device's data sheet.

What is the difference between latching current and holding current in a thyristor?

The latching current is the minimum anode current required to maintain the thyristor in the on state immediately after it has been turned on and the gate signal is removed. The holding current is the minimum current needed to keep the thyristor in the on state without the gate signal.

Why is it not advisable to use thyristors with high dv/dt waveforms?

Using thyristors with high dv/dt waveforms is not advisable because the rapid change in voltage can falsely trigger the thyristor, leading to unintended conduction. This is due to the high rate of change of voltage causing a breakdown across the anode-cathode junction.

Outlines

00:00

🔬 Introduction to Thyristor Device Physics

The lecture delves into the fundamentals of thyristors, highlighting their commercialization in 1960 and their role in revolutionizing power electronics by replacing thermionic switches. Thyristors are described as four-layer devices, essentially two diodes connected in series, with a unique forward blocking capability. The lecture emphasizes the importance of the gate for triggering the device and cautions against triggering while the cathode is more positive than the anode to avoid damage. The thyristor's structure, symbol, and physical appearance, including heat sink requirements, are also discussed, along with its potential for high power handling up to kilo-ampere ratings.

05:02

🔧 Power Handling and Thyristor Characteristics

This section discusses the thyristor's power handling capabilities, which can reach megawatt levels. It explores the two-transistor model of the thyristor, explaining how the injection of current can lead to high current flow and triggering of the device. The lecture also touches on the evolution of commutation and its impact on device design. The characteristics of different layers within the thyristor, such as the p-emitter and n-base regions, are examined, with a focus on how these layers contribute to the device's blocking capability and operational efficiency. The trade-offs between forward blocking voltage and switching speed are also highlighted, along with the importance of selecting the right device for specific applications.

10:05

📈 Operational Modes and Triggering of Thyristors

The paragraph explains the operational modes of thyristors, focusing on the forward blocking mode and the conditions under which thyristors transition from a blocking to a conducting state. It discusses the role of the gate in triggering the thyristor and the impact of voltage and current on this process. The paragraph also covers different methods of triggering, including avalanche breakdown and dv/dt gate triggering, and their implications for device operation. The importance of understanding the I-V characteristics for proper thyristor operation is emphasized, along with the significance of gate current in determining the forward blocking voltage.

15:06

⏱ Switching Characteristics and Time Constants

This section delves into the switching characteristics of thyristors, detailing the various time constants associated with their operation. It defines terms like delay time, rise time, gate turn-on time, and reverse recovery time, which are crucial for understanding the device's performance. The importance of the reverse recovery time in ensuring the thyristor can maintain its forward blocking capability is discussed. The paragraph also introduces key parameters such as forward breakdown voltage, forward leakage current, and forward conduction drop, which are essential for the design and application of thyristors.

20:10

🔋 Current Ratings and Operating Parameters

The lecture focuses on the various current ratings and operating parameters of thyristors, which are critical for their safe and efficient use. It covers peak working forward blocking voltage, repetitive forward blocking voltage, surge blocking voltage, and their implications for device selection. The paragraph also discusses the importance of understanding the dv/dt rating to prevent false triggering and the need for protective circuits like snubbers. Voltage safety factors and their impact on device life are also examined, along with current ratings such as RMS current, average current, surge current, and di/dt ratings. The significance of gate current specifications for triggering and operation is highlighted, providing a comprehensive overview of the parameters that influence thyristor performance.

25:12

📊 Data Sheet Parameters and Practical Design Considerations

This final section provides an in-depth look at the parameters found in thyristor data sheets, which are essential for practical design and application. It discusses threshold voltages, current ratings, gate current and voltage specifications, and power dissipation, providing a clear understanding of how to interpret and apply this information. The paragraph emphasizes the importance of considering temperature effects on ratings and the need to select devices that meet the specific requirements of the application. It concludes with a brief mention of modern devices like IGBT and IGCT, setting the stage for further discussions in subsequent classes.

Keywords

💡thyristor

A thyristor, also known as a silicon controlled rectifier (SCR), is a four-layer, three-terminal semiconductor device that can conduct electricity with a specific direction. It is primarily used for high power applications. In the script, the thyristor is described as having replaced thermionic-based switches like vacuum tubes due to its high power handling capabilities. The device is normally off until triggered by a gate signal or by exceeding a certain voltage threshold, which makes it a key component in power electronics.

💡forward blocking capability

The forward blocking capability refers to the thyristor's ability to block current flow when it is not triggered, with the anode voltage being higher than the cathode voltage (VA>VK). This is a critical feature for the safe operation of the device, ensuring that it only conducts electricity when intended. The script mentions that the thyristor is normally off and can block voltage until a certain threshold is reached, highlighting its importance in controlling high power circuits.

💡gate

The gate in a thyristor is the control terminal used to trigger the device from its off state to an on state. It plays a crucial role in determining when the thyristor should conduct electricity. The script explains that by injecting a small current through the gate, one can break down the junctional barrier, causing the thyristor to switch to its forward conduction mode, illustrating the gate's pivotal role in the operation of thyristors.

💡PN junction

A PN junction is a boundary or interface between a P-type semiconductor and an N-type semiconductor. The thyristor is composed of alternating PN layers, forming a structure that is essential for its operation. The script describes the thyristor as essentially two PN junction diodes connected in series, which helps to explain its unique electrical characteristics and its ability to block current in one direction until triggered.

💡commutation

Commutation in the context of thyristors refers to the process of turning off the device and preparing it to be turned on again. It involves the removal of the current that keeps the thyristor in its on state. The script touches on this by mentioning that once the current goes to zero due to the external power circuit, the thyristor can be turned off, which is a part of the commutation process.

💡latching current

The latching current is the minimum current required in the anode to keep the thyristor in its on state after it has been triggered and the gate signal is removed. It is an important parameter for ensuring the stable operation of the thyristor. The script specifies that the thyristor current must exceed the latching current value to remain in the forward conducting mode, indicating its role in maintaining conduction.

💡holding current

The holding current is the minimum current needed to keep a thyristor in its on state once it has been turned on. It is a key parameter for the continuous operation of the device. The script explains that if the current is above the holding current, the thyristor will stay in the forward conduction mode, which is essential for maintaining the flow of electricity in power electronics applications.

💡Avalanche breakdown

Avalanche breakdown occurs when the electric field across a junction becomes strong enough to cause a multiplication of charge carriers, leading to a large current flow. In the context of thyristors, it can trigger the device to start conducting if the voltage across the anode and cathode exceeds a certain threshold. The script warns that if the voltage is increased beyond the breakdown voltage, avalanche breakdown can occur, which is a critical consideration in the safe operation of the device.

💡di/dt rating

The di/dt rating of a device refers to the maximum rate of change of current that the device can handle without being damaged. It is an important parameter for devices like thyristors that are used in high power applications where current can change rapidly. The script mentions the need for a di/dt protecting circuit if the device undergoes very high di/dt, which underscores the importance of this rating in the safe and effective use of thyristors.

💡dv/dt rating

The dv/dt rating indicates the maximum rate of change of voltage that a device can withstand. It is crucial for thyristors to have a specified dv/dt rating to prevent false triggering, especially in applications with rapidly changing voltage waveforms. The script advises against using thyristors with high dv/dt waveforms, such as square pulses, which could lead to unwanted triggering, highlighting the significance of this rating in device selection and application.

Highlights

Thyristor, a key component in power electronics, was commercialized in 1960, replacing thermionic-based switches.

Thyristor's basic structure consists of two PN junction diodes connected in series.

The thyristor is normally off and can only be turned on with an external trigger.

The gate of a thyristor is crucial for initiating conduction by breaking the junction barrier.

Thyristor's forward blocking capability is due to the reverse biasing of the J2 junction.

The thyristor can be damaged if triggered with a gate signal while VK is greater than VA.

The four-layer thyristor is composed of p1 n1 p2 n2 regions, forming a three-terminal device with anode, cathode, and gate.

Thyristor can be visualized as two transistors, a PNP and an NPN, interconnected.

High power handling capabilities of thyristors can reach kilo-ampere ratings and megawatt levels.

The n-base region in thyristors is responsible for blocking capability and supporting large forward voltage.

High voltage thyristors use aluminum or gallium diffusion to create a deep junction in the n-base for reduced conduction loss.

Thyristor's switching speed is inversely related to the thickness of the n-base region.

Thyristor operation modes include forward blocking and forward conduction, influenced by anode-cathode voltage.

Gate triggering of a thyristor can be achieved with a potential VG applied at the gate terminal.

Avalanche breakdown and high dv/dt can lead to unintended triggering of thyristors.

Thyristor characteristics include forward blocking, conduction upon gate current application, and holding current requirements.

Switching characteristics of thyristors involve delay time, rise time, and turn-off time, crucial for device performance.

Thyristor's forward breakdown voltage (VBO) and forward leakage current are key parameters defined by data sheets.

Latching current and holding current are essential for maintaining the thyristor's on state and conduction mode.

Data sheets provide detailed specifications for thyristors, including voltage and current ratings, gate characteristics, and safety factors.

Thyristor's temperature ratings affect its current carrying capacity, with derating required at higher temperatures.

Modern devices like IGBT and IGCT are successors to thyristors, offering improved performance.

Transcripts

Welcome to our second lecture on device physics and the fourth lecture of advance power electronics

and control.

We shall continue with our discussion which was left you know previous discussions that

was thyristor.

So we have told that actually we have commercialized, this product is commercialized in 1960 and

it has replaced thermionic-based emission switches like vacuum tubes and all and it

is used for the high power handling capabilities and true power electronics starts with the

inventions and application of the thyristors.

So what essentially thyristor is, thyristor is essentially we can think of that one PN

junction diode, another PN junction diode is connected in series.

So essentially what happened, since when you applied a voltage actually it is a VA is>VK

or cathode.

Then, these junctions you know this J2 is automatically going to be reverse biased and

this junction J1 and J3 is forward biased and that gives features of forward blocking

capability, so this device is normally off.

Why?

If you apply a voltage VA>VK junction J2 is reverse biased; only leakage current will

flow.

Similarly, if VK is>VA then naturally J3 and J1 are reverse biased and then also it will

be blocked but you can make it on with the external devices or external way.

So forth this is and you know you got a gate, you can inject external current that will

basically break down the junctional barrier object and it comes into the forward conduction

mode.

Please mind it, never give a great trigger while VK is>VA, it may damage the thyristor.

So let us come into the discussions.

The thyristor is a four-layer, you have a four-layer you can name it p1 n1 p2 n2 like

that.

Three terminal devices you got anode, you got cathode and you got gate which each layer

consisting of alternatively PN type material.

For example, PN, PN the main terminals are labeled as anode and cathode across the full

four layers.

And the control terminal is called gate and it is attached to the p-type terminal near

to the cathode.

So this is the configuration of it and you know what happen if you actually truncate

the thyristors, then you can see two transistors, so it is said to be a two transistors model

PNP and NPN and in between they have got connections.

So generally thyristor is analyzed by the two transistors model for its turn-on applications.

So different kind of thyristors appearance, this is the symbol of the thyristors.

This anode, cathode and gate and you will have a different kind of pictures which is

basically the heat sink, it required to put onto the heat sink.

This is anode and ultimately it will be go into the heat sink and will can tighten the

screws and there is a different kind of segments and current handling capabilities of the thyristors

in fax devices, it can go as high as kilo ampere rating.

So power handling capabilities of these devices can go as high as you know megawatt level.

So this is the actually a truncated version of the thyristors.

So we can visualize as two transistors model, one is PNP; another is NPN where actually

Ig is injected.

Thus, you know if you write the KCL from this point to this point, ultimately Ia becomes

alpha Ig+ICB1, this is basically the base current of transistor 1 and ICB2 is a base

current of transistor 2.

And you will find that 1-alpha 1+alpha 2.

Here this alpha 1 and alpha 2 are essentially are not constant, this value can change depending

on the value of injections of this value and generally this value is alpha 2 generally

changes and it may so happen that by changing this value, this denominator can be made close

to zero and thus high current will flow and we say that thyristor is triggered or latched.

And it will continue to flow till some external action has been added to actually put it off

or commutation.

Commutation itself is a big chapter of discussions but with the invention of the GTOs and all

those things there is literally phasing out.

So let us come to the different layers and its concentrations.

So it is called p-emitter region.

This is called n-base region ((then again)) (07:09) it is called p-base region and it

is n-emitter region.

So this is the model and a highly resistive region n-base region is present in all thyristor

to give a blocking capability and it is the region n-base and associated junction J2 which

must support the large applied forward voltage that occurs when switch is off or the forward

blocking state or the non-conducting state, so this is the region.

High voltage thyristors generally made by diffusing aluminium or gallium into both the

surface to create p-doped region forming a deep junction in the n-base.

So that will reduce the all-state conduction loss.

The higher forward blocking voltage of the thyristors, the thicker n-base region, it

is basically used; however, increasing the thickness of this resistive region will actually

will reduce the operations, reduce the faster operation that means it will slower the turn-on

and the turn-off.

So it will take larger time to turn it on and require higher gate current and also you

know you have to do the commutation put it off when actually we may have a natural commutation.

In case of the rectifier operation, when you applied to the AC sources, you get a negative

voltage applied cathode to anode.

So thus turn off also will be slower and it will be suitable for the low frequency switching

devices because most of the trap charge required to be removed and that takes lot of time than

the faster devices.

So there are something we require to trade it off, we have to put according to the applications.

So if the thyristors has a high blocking forward voltage generally it is very slower device

and switching time will be actually slow.

Between forward blocking voltage rating and the forward voltage drop during conduction

should be kept in mind.

Since high voltage thyristor generally of the aluminum and the gallium drop surface,

so that gives a higher voltage blocking capability.

But it also increases the all-state conduction losses or the resistance of the devices.

So we have to trade it off.

For this reason, we required to choose suitable devices.

We should not choose a high blocking thyristors where we will find pretty high conduction

losses and reverse you choose devices with a low conduction losses but it cannot sustain

that forward blocking capability or the reverse blocking capability.

Then, circuit will burn simply.

So for this reason, designer has to judicially use these features of the thyristor.

Operation, when anode is positive potential that in VAK is positive with respect to the

cathode and no voltage is applied to the gate, it is said to be the forward blocking mode.

The junction J1 and J3 are the forward biased while junction J2 are reverse biased and J2

will actually block the whole voltage.

If VAK is increased beyond the breakdown voltage of BO that has been prescribed in the data

sheets for the thyristors, Avalanche breakdown of J2 takes place and thyristor start conducting.

But sometime it may damage the thyristors because you know when actually it start conducting,

current is also high and it has got a considerable voltage drop across the junction and that

if you properly heat is not dissipated this mode may damage the thyristor.

If applied a potential VG at the gate terminal with respect to the cathode, the breakdown

of junctional voltage J2 occurs at considerably lower voltage.

It can be as less than 10 times less or 20 times less depending on the amount of the

current you are injecting.

By selecting the appropriate value of the VG, the thyristor can be switched on on a

sudden state.

So this is the I-V characteristics of the thyristors, once VG is zero, so this zone

is called the forward blocking region and the current leakage current will flow through

it and thereafter what happen forward leakage current will flow through it and thereafter

when it will cross the value of VBO, it will be triggered and current will flow from this.

If you keep this value of IG of some value let say here around half of the VBO or two

third of the VBO, it can actually come this point to this point.

And it will give you a drop of very small drop.

Similarly, you can turn it on from the VBO, again you please remember that IG2 should

be much greater than IG1.

So larger the gate current, you get lower the forward blocking voltage.

So apart from the gate triggering, there is a different method of gate triggering, Avalanche

breakdown that is actually high voltage applied across the anode and cathode.

Dv/dt gate triggering if you apply high rate of change of voltage that also leads to the

triggering, for this reason it is not advisable to use thyristors in pulse kind of waveform.

If you have a square pulses which has a very high dv/dt which may falsely trigger the thyristors.

So for this reason, will not use it most of the cases and light activation thyristor there

is a special kind of thyristors when the depletion region can be actually reduced by activation

of the light or doping charges.

And high junction voltage and what we generally use is that gate triggering.

Gate triggering is something we use for the triggering thyristor that is a common mode

of practice.

A different kind of gate triggering can be there that is RC or we can have a UJT based

gate triggering that different kind of gate triggering circuit may be used.

So characteristics of the thyristors let us come to it.

So blocking occurs when reverse biased current is applied depending on the gate current.

When forward biased and the gate current is applied, conduction takes place and it will

be high current and actively it will be blocked by the load of the system.

Once turn on goes on, gate is no longer required.

You can put up the gate, so it will just require to turn it on.

Once it is turn on, gate circuit may be put off and thus you can avoid a constrained dissipation

of the current across the gate.

Gate turn off when decreasing current goes to zero because of the external power circuit

also.

Now this is actually the switching characteristics of the thyristors.

So this is actually the voltage across VAK that is anode to cathode voltage and it will

drop.

You can find that current through the thyristor will take around 10% time to actually to its

peak value, it would whatever time it will take 0% to 10% or the leakage current you

can assume to be 0% to 10% of the load current or the final rated current, so that current

is said to be td or the delay time.

Thereafter, you will have 10% to 90% we say that is a rise time, so faster is the rise

time so faster that will be a faster device.

If rise time is slower, it will be slower device.

Thereafter, it takes you know some amount of time to actually settle down and tgt is

a gate turn on time.

Similarly, we come to the reverse recovery time, reverse recovery time totally depends

on the current.

Reverse recovery time is the total current actually trr and this one is actually tgr

and total time is said to be the turn off time that is represented by the tq.

Again, actually like that we require it is a very important feature of the reverse recovery

time.

So for this reason, you know when it will be off, when both are recover, the recovery

time means actually it has got a forward blocking capability.

But if you have a false triggering gate it will turn conduction.

For this reason, we got a forward recovery time or this total actually combines and then

we can say that thyristor has hold the forward blocking capability.

So you have to wait till time trr+tgr.

So there are few important terms that is forward breakdown voltage VBO that is this has been

prescribed by your data sheet, it is done by the destructive test of the devices generally

it does not survive after the test.

So we generally will do with the few samples and presented in the data.

So this is VBO and that is called forward breakdown voltage and once it was actually

in a forward mode, forward blocking mode some amount of current will flow that is called

forward leakage current.

That is around 10 to the power 4 times lower than this actually the thyristor current and

thereafter you have a gate triggered.

So accordingly voltage will change and this is a forward conduction drop.

Generally, it slants almost it, due to this ohmic losses, it will be little bit slanted,

so if it is because you know as there is two diode in series.

This model is essentially can we think of that two diode put into the series.

And since the silicon based diode of course you can assume that both will have a junction

and drop of J1 and J3 in forward conduction mode of 0.7 and 0.7 that gives you the 1.4

volt but depletion region is made in a such a way by dropping of the aluminium and other

things but forward conduction mode will try to restricts less than 1.4 volt.

That is actually one of the technical advancement has been achieved in case of the thyristor.

There are two important parameter, one is called latching current.

Latching current is associated with the turn-on process.

Once thyristors is put on, thyristor current required to go more than the value of IL.

Then, if you remove the gate, then also it will be in a forward conducting mode.

So thus the minimum anode current is required to maintain the thyristor in on state, immediately

after its turn on and gate signal has been removed.

Same way holding current, what is holding current?

This current should minimum current it should hold to keep it in a conduction mode.

So that is called a holding current and that is associated with the turn on of the thyristors.

If the current is above, the holding current, thyristors will stay in a forward conduction

mode.

The minimum anode current maintain the thyristor in an off state.

And of course from this figure it is quite clear that this holding current should be

less than the latching current.

Now these are the few parameters you know it is quite important while analysis the thyristors

and use it the thyristors.

First of all, peak working forward blocking voltage or forward off state voltage VDM.

So this is basically the VDM which is quite important because since the repetitive supply

is there, so this voltage has to be block, you may trigger this point, you may trigger

this point, you may trigger this point, you may trigger this point.

So safely it should be able to block the value of the medium then value will be prescribed.

So peak repetitive forward blocking voltage, this is VRM because sometimes we may have

a notch and notch actually follows so that value will be actually pretty peak repetitive

forward blocking voltage.

Peak non-repetitive or the surge blocking voltage if all of a sudden high voltage comes

that is said to be the surge and it has not has ((periodic occurrence)) (21:20).

Then, that voltage is said to be the actually VDSM and the VDSM value also will be prescribed.

Some notches may come, maybe after one hour or two hours or even after a day.

So that value actually said to be the VDSM.

Peak working reverse voltage, it is same so as this actually forward voltage, this is

basically VRWM this one.

Then, peak repetitive reverse voltage, this one it is same as this one but it is in a

reverse direction.

Peak non-repetitive surge, so this will be this one and this has to be actually almost

reciprocal to the forward voltage and we required to understand that forward dv/dt rating.

So this is quite important, you know that supply voltage undergoes some changes if it

is say sinusoidal wave it is quite slow.

If it is a pulse kind of voltages, then it will have a very fast dv/dt.

So dv/dt rating of this device required to be prescribed, otherwise we require to put

a dv/dt protection circuits that is called snubber.

We shall take out the circuit protections in totality.

Thereafter, voltage safety factors that is VSF that is given by peak repetitive reverse

voltage by 2*RMS value of the voltage.

So some value will come out accordingly life of the device will be decided.

So more the safety factor more will be the life of the device but definitely cost of

the component will go high and finger voltage of SCR that is called FV.

So these are the few parameters has been prescribed in your data sheets and we will continue to

actually have operating on those data sheet for the practical design aspects.

Apart from that, we have current ratings, that is same that is maximum RMS current rating

and thereafter maximum average current rating, mostly it will be for the DC value, maximum

surge current rating, all of a sudden if high current comes it has to sustain and thyristors

I square R rating.

So for the conduction losses was the one it is on state and thereafter di/dt rating, so

if it undergoes very high di/dt, then also it can damage the thyristors.

For this reason, we required to put a di/dt protecting circuit and that we will discuss

about the di/dt and dv/dt protections but thyristor has to ensure that we will have

its di/dt rating; we are operating in a separate sheet.

Thereafter, we have some specification on the gate current.

So gate current to trigger there will be a minimum current there is a safety operation

where it is not triggered because noise also gives you some amount of the gate current.

But that should not trigger the thyristor falsely, so for this reason, gate current

to trigger that value will be there.

Similarly, we will have some value will be there actually, we shall come into the discussions.

So gate voltage to trigger, there will be some voltage.

So this VG and this IG, this is the minimum value.

This zone will not trigger; this may come due to the noise.

So non-triggering gate voltage, this is basically non-triggering gate voltage.

And peak reverse gate voltage, the maximum voltage you should apply.

You should not go beyond that; we may damage the gate.

Peak reverse gate voltage, again that comes into the picture in a reverse mode.

So you should not allow actually the reverse gate voltage.

Average gate power dissipation, this is the power line so you have to fix into it in the

power line.

You should not go beyond the power dissipation.

Otherwise, the gate circuit will fail and peak forward gate current that value also

will be specified by the thyristors.

So this is the data sheets of the thyristors.

You see that you know there are some values.

It has a forward blocking capability of 1200 volt and it can carry as high, we are discussing

a diode of 3 ampere or 8 ampere and it has a power handling capability of the 50 ampere

but you see this ratio, this gate current is 1000 times less, so this is the efficiency

counts, the IGT is actually 50 milliampere.

And all the values is provided what has been discussed into the data sheets.

So in a different temperature level in a conduction temperature 50 amperes.

If it is temperature rises to 100 degree centigrade, it has to be considerably d-rated, it has

to be operated to the 31 ampere and all the data has been prescribed.

So peak gate current can be 8 ampere, peak power dissipation should be 1 watt.

And maximum peak reverse voltage is 5 volt.

Similarly, you will see that actually what should be the IGT, IGT should be it actually

prescribed that is 50 milliampere but you can operate anywhere in between actually 8

to 50 so that you can turn it on a different voltages.

Similarly, holding current has been prescribed when gate is open.

It is 500 milliampere.

Similarly, latching current has been prescribed, that should be actually 1.2 times of the IGT.

So from there you can calculate and this value is generally it is actually 1 to 5 milliampere

and value of this dv/dt also is given that is actually 1000 volt per microsecond.

Similarly, value of the tq that is the turn off time, you can see that, that is in the

range of the 100 microsecond.

Please recall that you know it is quite slow, in diode we have come out, we have seen a

fast diode having a turn off time in nanoseconds.

And snappy diode will have around 2 or 1.2 microsecond but this will take a considerable

high amount of time to turn it off.

So turn it off of this devices it is quite slower because of the trap charges in junction

J2 okay.

We shall continue to our discussions.

These are the ratings you can follow.

So these are the threshold voltages and IDRM and RDRM.

So all those data has been actually explained so that student can take out for the design

purpose and how to read the data sheet properly.

We shall continue till few aspects of the thyristors in our next classes and followed

by some modern devices like IGBT and IGCT.

Thank you so much for your attention.