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MOSFET (Si/SiC) Forum Discussions

NXTY_Shibata
Level 2
Level 2
5 replies posted First solution authored 5 questions asked

I have been measuring SiC MOSFET with EVAL_PS_DP_MAIN and the daughter board. But it currently not good since there is very noisy from waveform. But I noticed it became better after I connected shunt to Id150 point in mother board. So I'd like to confirm to do better measurement.

The things to be checked are following 2 points.
1.Is this circuit required to set shunt or jumper in on Id150 to implement correct measurement? It's described in attached  "Infineon-Schematics_EVAL...".
2.The reason why 4 resistors are connected to capacitors between HV_VDC and GND. Is these used as RC snubber? This is described in attached "SiC-MOSFET_EVAL Board.pdf".

If there is a quesiton, please let me know.

Best Regards,

Shibata@Nexty

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1 Solution
Neo_Qin
Moderator
Moderator
Moderator
100 sign-ins 10 likes received 50 replies posted

Hi @NXTY_Shibata  san,

This is my first time to reach out to the EVAL_PS_DP_MAIN evaluation board, please forgive me for answering the question_2 first, so that you can know that we are working on this thread.

I think these 4 resistors have the following functions:

1.  Clamp the ringing spikes that may appear on the HS_HV_VDC network, avoid capacitor damage due to overvoltage.

The previous version evaluation board provided test data (refer to the figure 14 of attachment). The peak VDS voltage of S1 may reach 960V, while the withstand voltage of C152/C153 is only 1000V. The series resistors can improve the reliability of the circuit.

So, I agree with you that it's a snubber circuit.

2.  If the capacitor is regarded as a first-order filter, there is a resonance point, which will not weaken the noise but strengthen. A small resistance in series with the capacitor can play a damping role.

Of course, this comes at a cost. On the one hand, it increases the power loss (the power loss is shared by two resistors in parallel). On the other hand, it reduces the fast attenuation speed of the filter beyond the cut-off frequency.

Regards,

Neo

 

 

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2 Replies
Neo_Qin
Moderator
Moderator
Moderator
100 sign-ins 10 likes received 50 replies posted

Hi @NXTY_Shibata  san,

This is my first time to reach out to the EVAL_PS_DP_MAIN evaluation board, please forgive me for answering the question_2 first, so that you can know that we are working on this thread.

I think these 4 resistors have the following functions:

1.  Clamp the ringing spikes that may appear on the HS_HV_VDC network, avoid capacitor damage due to overvoltage.

The previous version evaluation board provided test data (refer to the figure 14 of attachment). The peak VDS voltage of S1 may reach 960V, while the withstand voltage of C152/C153 is only 1000V. The series resistors can improve the reliability of the circuit.

So, I agree with you that it's a snubber circuit.

2.  If the capacitor is regarded as a first-order filter, there is a resonance point, which will not weaken the noise but strengthen. A small resistance in series with the capacitor can play a damping role.

Of course, this comes at a cost. On the one hand, it increases the power loss (the power loss is shared by two resistors in parallel). On the other hand, it reduces the fast attenuation speed of the filter beyond the cut-off frequency.

Regards,

Neo

 

 

Hi Neo-san,

Thanks for your kindness!!

My Question 1 seems my misunderstanding, so it's not important any more.

My assumption seems correct from your answer, I agree with your  opinion. Recently, RC snubber has been avoided compared to C snubber. So this was my unclearness but it became clear now.

Regards,

Shibata

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