Electrical Engineering

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Marla

01:08

@yogece I agree with W5VO. Even though I have used the same Semikron device on a 670 volt buss (protection transistor) @100% duty cycle, I don't know how to address your questions.

1 hour later…

yogece

02:35

@Marla i understood we can use IGBT in continuous conduction mode at that time Tj &Tc and Vce & Ic are the limiting factors. since you have used the Semikron device @100 duty cycle i have few questions to ask you

1)How much current flowing through the device and What is the type of Load?

2)How long the device kept @100% duty?

3)How much was the initial Tc and steady state Tc?

4) How much was Ta?

5) which topology used? single switch?(high or low side switch?) half bridge or full bridge?

Marla

03:12

@yogece . .in the use I spoke of, I don't remember the thermal details. Thermal calculations start with heat sink temperature. Then there are barriers to heat flow (thermal resistance). Heatsink to case resistance is dependent upon many things and Semikron gives great detail about the surface and flatness of their mounting surface of the case. Semikron also details what finish and flatness your heatsink should be. . . . continued. . .

I decided on a junction temperature at 125 degrees C. Then worked backwards through the thermal calculations to determine how much current I could push through the transistor.

yogece

@Marla Thanks for the immediate reply.Your experience is my age:)

Marla

You have two endpoints, the junction temperature and heatsink temperature.

In your case, you also have one switching loss per cycle.

This will need to be accounted for also.

yogece

how far the simulation(Thermal and electrical) correlates with the bench setup. i have seen some papers they have mentioned +/- 30% but in that paper they haven't shown the setup and simulation details much

Marla

Is this the direction you are going?

yogece

i am wondering i couldn't find a single resource about IGBT based chopper for DC motor control because there they would be talking about the Duty cycle Vs Temperature and other details

Marla

03:21

I can't say about simulator versus real, but you have to place your trust in the data sheet and the manufacturer.

Just add your switching loss and conduction loss total, and then use the thermal resistances given by Semikron.

yogece

i have already sacrificed some IGBTs and learnt few lessons. now i thought of going in a different route that's why i am looking for Simulation versus Real correlation

Marla

In the many years we used Semikron devices, the data sheets never led me wrong. And it was discipline on our part go assure our heatsinks finish was proper and that proper torque on the bolts.

Inevitably, failures occurred which were problems with our heatsinks or methods.

And the IGBTs are not cheap. As you know

yogece

and one more thing i came to know the manufacturers of IGBT use simulation software's to generate various characteristic graphs of IGBT that means they won't even check every parameters in real time. I got this information from "NIST manual about IGBT model" i have that document with me

this is the reason for having good hope with simulation tools. Many manufacturers use PLECS based simulator. Infineon uses PLECS online simulator

I dont know about the Semikron Semisel simulator. NIST documents talk only about "Saber" simulator

Marla

03:39

You might want to start with the specifications of your heatsink and compare to what Semikron says to use.

The surface finish is critical when using high power devices.

yogece

@Marla Thank you so much indeed for your help. And one thing pestering in my mind for long time "Why do people help the unknown persons without expecting anything from them "

Marla

I am retired, and it keeps me up to date and not forgetful.

Also, what is wisdom if it is not shared.

yogece

i am from india and i am a member of few whatsapp & telegram technical groups but most of the time people don't help each other.

Marla

I have no competition ;)

yogece

:) if you write any blog or articles can you share me the link

Marla

03:49

I haven't written any blogs.

yogece

bye for now....

2 hours later…

yogece

05:50

Q: IGBT contactor design

I found this circuit in an older post. I was thinking about using this in place of a contactor to break under load. The load would be at 500V 300A DC. There would be overcurrent protection in line with this. I do realize that this would be less efficient than a contactor and maybe more expensive....

@JonRB Any suggestions?

Q: Is it possible to make an IGBT to work at duty cycles up to 100%?

I am designing an IGBT based chopper with single Low side switching IGBT (chosen low side switching because ease of driving the IGBT.) There are plenty of resources available for SMPS (buck, boost, buck-boost,) PFC chopper, inverters, welding power sources, UPS and motor control applications. ...

power-electronics igbt powermosfet

10 hours later…

W5VO

15:54

@yogece manufacturers make models from measured data. They also make the datasheet based off of measured data. The models are not absolute, or always correct, and they may behave erratically if you do something odd.

4 hours later…