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true_kobefans
Level 1
Level 1
5 sign-ins First reply posted First question asked

hi all! When using the FF450R12KT4 module,failures occur frequently.Measure the failed IGBT modules,the G and C  are often short-circuited,Sometimes there is also a short circuit between C and E.The bidirectional TVS  on the drive board is also short-circuited.The gate drive voltage is +15V/-8V,the bidirectional TVS is SMAJ16CA. why and how this happened?THANKS~

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1 Solution
Guru_Prasad
Moderator
Moderator
Moderator
250 replies posted 100 solutions authored 25 likes received

Dear @true_kobefans 

Greetings!

The current flowing through the Cgc will create voltage spikes when the switch is OFF. due to that voltage can be generate more. you can refer the below image.

Guru_Prasad_0-1683691662319.png

here the voltage spike is depends on the switching frequency and voltage rate of raise which is  dv/dt.  if the voltage spikes are with in limits it is fine.

is it possible to capture the Vgc ?

you mentioned one  point "The bidirectional TVS  on the drive board is also short-circuited"  please share the schematic of your driver where is the TVS diode is connected? 

Thank you

Guru

 

 

 

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Guru_Prasad
Moderator
Moderator
Moderator
250 replies posted 100 solutions authored 25 likes received

Dear @true_kobefans 

Greetings!

Turn-on or turn-off of IGBT can cause high dVce/dt. Displacement currents flow through the parasitic
capacitances of power transistors and may lead to an unintended turn-on of IGBT. For example, in a half bridge configuration, the switched-off IGBT tends to dynamically turn on during turn-on phase of the opposite IGBT.

Guru_Prasad_0-1683203436760.png

 

The Gate to Collector short will happen because of the high voltage spikes which were generated due stray inductance of DC side. so to avoid this spike you can do below practices,

1)Try to optimize DC side stry inductance  

2)use miller cap circuits

3)optimize the speed of the device.

Thank you

Guru 

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Dear @Guru_Prasad 

Thanks for the suggestions!

I've noticed the crosstalk issues with full-bridge circuits.I wasn't using Miller clamping circuits at this moment because of the spike on the Vge is  far below the Vgeth and the Gate-emitter peak voltage.Also,I'm a little confused about "The Gate to Collector short will happen because of the high voltage spikes which were generated due stray inductance of DC side".I hope you can explain a little more specifically about this. Stray inductance of DC side may  result in excessive VCE,but it's normal for me to measure Vce.The switching speed is already slow because the gate resistance is large(5Ω).

true_kobefans_0-1683294730775.png

Expect to get a response from you!

Thank you

 

 

PREVIEW
 
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Guru_Prasad
Moderator
Moderator
Moderator
250 replies posted 100 solutions authored 25 likes received

Dear @true_kobefans 

Greetings!

The current flowing through the Cgc will create voltage spikes when the switch is OFF. due to that voltage can be generate more. you can refer the below image.

Guru_Prasad_0-1683691662319.png

here the voltage spike is depends on the switching frequency and voltage rate of raise which is  dv/dt.  if the voltage spikes are with in limits it is fine.

is it possible to capture the Vgc ?

you mentioned one  point "The bidirectional TVS  on the drive board is also short-circuited"  please share the schematic of your driver where is the TVS diode is connected? 

Thank you

Guru

 

 

 

0 Likes