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In the Infineon Application Note, two of the parameters they've used to calculate the switching loss of the MOSFET are Vds(on) and Vds(off).

Vdson vs Vdsoff

  • Is the Vds(off) the blocking voltage?
  • Where do they obtain the Vds(on) and Vds(off) values from? Are they:
    1. arbitrarily chosen
    2. taken directly from the datasheet
    3. dependent on the converter it's used in
  • If it's the third option, how to calculate the Vds(off) specifically?

Reference:

Application Note: https://www.infineon.com/dgdl/Infineon-ApplicationNote_MOSFET_CoolMOS_How_to_select_the_right_CoolMOS-AN-v01_00-EN.pdf?fileId=db3a304412b407950112b40acf580693

MOSFET Datasheet: https://www.datasheetarchive.com/pdf/download.php?id=76cd77451b2171be9a0ed7cbcf732382c7b37e&type=M&term=SPP04N60C3

Richard Escobia
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    It depends also on the transition speed during shutoff with current still flowing as the voltage rises. – Tony Stewart EE75 Aug 25 '20 at 00:11
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    You should probably reference the files directly from the manufacturer, personal files could be suspect. – Voltage Spike Aug 25 '20 at 00:35
  • Ah let me see. I skimmed the app note, then slowly read S 11 switching losses. I noticed that they mentioned the term "***measurement***" "often". So my quick and dirty conclusion is that they are ***measuring things*** under different test conditions and perhaps also use a bunch of devices to collect statistical values and draw graphs (Fig 5 ~ 8). In other words, they might, by trials and errors, arbitrarily vary parameters, say freq, current etc, and *** measure*** Vds on/off etc. PS - I am a power MOSFET hobbyist. I use US$300 Rigol DS1054 50MHz 4Ch storage scope to ***measure*** things. – tlfong01 Aug 25 '20 at 03:19
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    Thank you for your insight @tlfong01 You're right, the information here is based on the "investigations of a usual boost converter driven in the double pulse measurement mode." But if Vds(off) were taken directly from the test circuit, then the Correcting Factor during the turn off switching, CFoff(Vds(off)), should be equal to 1 in the DCM calculation in Section 12. I want to use this method to select MOSFETs for my converter, but I'm stumped as to how to figure out what Vds on/off is, since my thinking is that Vds is 0V(ideal) during turn on switching, but here it has a value of 380V – Richard Escobia Aug 25 '20 at 04:26
  • Thank you for your nice words and encouragement. So you are playing with something me newbie never heard of: "***Boost converter driven in the double pulse measurement mode***". Of course me neither heard of "Correcting Factor during turn off switching, ***CFoff(Vds(off))***". You also remind me of the scary ***380V Vds*** which I never imagine of and why it comes up (Back EMF, perhaps?). Anyway, me hobbyist is happy to have a glimpse of what the pros are developing things with MOSFETS. Cheers. – tlfong01 Aug 25 '20 at 04:52

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