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MS_19060803
Level 4
50 replies posted 100 sign-ins 5 solutions authored
Level 4

Hi all,

The RBSOA(reverse bias safe operating area) is written on the data sheet.
Could you please show me the SCSOA(Short circuit safe operating area) both at 25 degrees and 150 degrees, if you have?

Also, could you please show me the maximum allowable loss value at short circuit, if you have?

Best regards,

MS

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1 Solution
AZIZ_HASSAN
Moderator
Moderator 100 sign-ins 50 solutions authored 10 likes received
Moderator

Hi,

1) The maximum value for current we don't have because as I explained  you earlier, the maximum  current not only depends upon the device but also depends upon  the leakage inductance  (which is a system parameter) and we might not emulate your system parameter here.

2) Another point  in short circuit is , the peak current is not very important rather the energy which is dissipated during the short circuit is important( which seems to be perfectly fine in your case waveforms).

3) Yes at Vcc=180V, the current of peak 3500A for 7 usec is ok. 

So, in general  when you do short circuit at lower voltage and at your system parameters (mainly leakage inductance), the best way to check the proper operation is the gate driver should detect the desaturation fault and stop the device successfully. As long as this is happening, the waveforms are good and device is safe. 

I hope you understood my explanation.

Thanks,

 

BR,

AZIZ HASSAN

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AZIZ_HASSAN
Moderator
Moderator 100 sign-ins 50 solutions authored 10 likes received
Moderator

Hi,

Thank you for posting your query at Infineon community.

1) We can understand that unlike RBSOA, SCSOA is not  given in form of graph. However, in data sheet the SCSOA values is given in the table. I hope the table is sufficient to understand the short circuit area.

AZIZ_HASSAN_0-1642056536145.png

2) Generally, for short circuit the losses are not required because its once in a while event and as  long as the short circuit occurs within the specifications, no damage will happen to device.

However, you can estimate the losses using a oscilloscope  by doing a dead short circuit test in your two pulse set up.

 

BR ,

AZIZ HASSAN

 

 

 

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MS_19060803
Level 4
50 replies posted 100 sign-ins 5 solutions authored
Level 4

Thank you for your reply.

I have additional questions.

SC data is 2800A at 25 degrees and 2000A at 150 degrees on the data sheet, but they are typical value.
Could you please show me the maximum value?

When Vcc is 180V, is it acceptable to 3500A at 25 degrees for 7us?

Is there any problem with the waveform below?

MS_19060803_0-1642066702530.png

Best regards,

MS

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AZIZ_HASSAN
Moderator
Moderator 100 sign-ins 50 solutions authored 10 likes received
Moderator

Hi,

Thank you for understanding.

To answer your additional query regarding  the dead short circuit waveform, may I know the leakage  inductance, di/dt value during turn on at rated current and gate voltage  waveform during short circuit.

Generally, this peak current is limited by the device impedance , path (circuit leakage inductance) and the voltage applied across the device during short circuit. If you do short circuit at voltage lower than rated , the peak current will be lower with  more oscillations and can withstand for more time compared to short circuit at rated voltage (360V).

Prima facie, the nature of the waveform looks perfectly fine to me. However, please share the leakage inductance and di/dt  value.

BR,

AZIZ HASSAN

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MS_19060803
Level 4
50 replies posted 100 sign-ins 5 solutions authored
Level 4

Thank you for your quick reply.

Do you mean the red circle point below is di/dt?

MS_19060803_1-1642081768771.png

I couldn't understand what you mean by the leakage inductance.
Could you please tell me in detail what the leakage inductance is?

Best regards,

MS

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AZIZ_HASSAN
Moderator
Moderator 100 sign-ins 50 solutions authored 10 likes received
Moderator

Hi,

Yes the rise in current in red color is the di/dt. However, I am requesting  the di/dt at rated current not at short circuit.

Leakage inductance is nothing but parasitic or loop inductance of the complete set up( starting from DC+ to bus bar to DC-). It is generally inevitable and comes mainly due to the path travelled by the current (straight or curve while travelling from DC+ to DC-) and joints ( where the hardware are connected) in the complete circuit.

This leakage inductance leads to voltage overshoot across the CE terminal of IGBT during turn off.

By doing the two pulse test, one can measure the leakage inductance at the time of turn on or turn off.

Following is the method to measure leakage inductance.

1) During turn on-

When you turn on the device at rated current, the voltage will go down to zero in two steps. First the voltage will fall slightly to a non zero value and will stay for some time and after some time it will finally  fall to zero. The first fall of voltage to non zero value is due to leakage inductance.

During the constant voltage region after first fall, you can measure the rising di/dt and the amount of voltage fall from rated to constant voltage zone. Once you get the two values, you can calculate the leakage inductance value by a simple equation of voltage across inductor.

2) During turn OFF-

While turning  off, the voltage waveform will have some overshoot and will go higher than the dc bus voltage and after some time will come back to rated dc bus voltage. That difference in voltage from nominal dc bus  to peak overshoot voltage is due to leakage inductance.

During that overshoot, you can measure the di/dt and voltage difference to calculate the leakage inductance value.

I hope you understood.

Note- To finally comment on your short circuit waveform which  initially  looks fine, gate voltage waveform is required.

BR,

AZIZ HASSAN

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MS_19060803
Level 4
50 replies posted 100 sign-ins 5 solutions authored
Level 4

Hi,

They remeasured the waveform including the gate waveform at short circuit.

MS_19060803_0-1642494249338.png

The conditions for measuring di/di and inductance are as follows.

The voltage is 300V and the current is 700A.

At the time of turn-off, di/dt = 4.2A/ns, Inductance = 30.7nH.
At the time of turn-on, they couldn't measure those because the voltage didn't stay for any time.

Could you please give us your opinion on the waveform under this condition?

Best regards,

MS

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AZIZ_HASSAN
Moderator
Moderator 100 sign-ins 50 solutions authored 10 likes received
Moderator

Hi,

The waveform of gate voltage, collector current and collector voltage waveform looks fine. The values shared seems to be fine.

However, I requested the di/dt  at rated current and rated voltage of your operation not at short circuit.

Please share the two pulse result at rated voltage and current. The short circuit result are ok.

BR,

AZIZ HASSAN

 

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MS_19060803
Level 4
50 replies posted 100 sign-ins 5 solutions authored
Level 4

Hi,

Thank you for your reply.


Although you said "the short circuit result is OK", you requested di/dt value. Why do you need di/dt value?

If you really need the value, is it right to measure turn-on and turn-off at the rated current and voltage rating of their system?
Or do you mean the measurement at the rated current (400A) and rated voltage (600V) of FF400R06KE3?

Best regards,

MS

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AZIZ_HASSAN
Moderator
Moderator 100 sign-ins 50 solutions authored 10 likes received
Moderator

Hi,

Thank you for your reply.

To be very frank the di/dt is not needed now because your short circuit waveforms looks fine. However, just to on safer side I requested this waveform or data  at your system rated conditions. The reason for asking the di/dt waveform at operating conditions was just to make sure that the IGBT and gate driver are working fine at operating conditions as well and is your leakage inductance making you to go in clamping zone or near to it in every switching cycle or not.

Since, we have not seen your operating condition waveform,  the IGBT waveform at operating condition will give us  full satisfaction that the system works fine.

 

BR,

AZIZ HASSAN

 

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MS_19060803
Level 4
50 replies posted 100 sign-ins 5 solutions authored
Level 4


Hi,

Thank you for your support.

Could you give us your opinion on the following questions which I asked in your website on Jan 13, 2022?

SC data is 2800A at 25 degrees and 2000A at 150 degrees on the data sheet, but they are typical value.
Could you please show me the maximum value?

When Vcc is 180V, is it acceptable to 3500A at 25 degrees for 7us?

Best regards,

MS

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AZIZ_HASSAN
Moderator
Moderator 100 sign-ins 50 solutions authored 10 likes received
Moderator

Hi,

1) The maximum value for current we don't have because as I explained  you earlier, the maximum  current not only depends upon the device but also depends upon  the leakage inductance  (which is a system parameter) and we might not emulate your system parameter here.

2) Another point  in short circuit is , the peak current is not very important rather the energy which is dissipated during the short circuit is important( which seems to be perfectly fine in your case waveforms).

3) Yes at Vcc=180V, the current of peak 3500A for 7 usec is ok. 

So, in general  when you do short circuit at lower voltage and at your system parameters (mainly leakage inductance), the best way to check the proper operation is the gate driver should detect the desaturation fault and stop the device successfully. As long as this is happening, the waveforms are good and device is safe. 

I hope you understood my explanation.

Thanks,

 

BR,

AZIZ HASSAN

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