Losses in LTSpice

[teslaaa]

Hello everybody,
i am new here and I tried to estimate some losses in LTSpice using a DPT for several devices. However, I am not getting reliable results, since the voltage is just linearly increasing and my drain source voltage is not looking like expected. If there are some hints, where I have some mistakes, it is kindly appreciated! Attached there are the files.

Thanks in advance!
Best regards

 

[Harald Kapp]

You have floating nodes:

ERROR: Node u1:x1:x_rs:m is floating and connected to current source u1:x1:x_rs:G1
ERROR: Node u1:x1:x_rd:m is floating and connected to current source u1:x1:x_rd:G1
ERROR: Node u2:x1:x_rs:m is floating and connected to current source u2:x1:x_rs:G1
ERROR: Node u2:x1:x_rd:m is floating and connected to current source u2:x1:x_rd:G1

Try connecting the respective source and source_sense of each GaN FET like so (you'll have to remove the net named MID to avois a collision of net names):

 

[teslaaa]

Hi Harald,
Thanks for your response and time. I modified my circuit and got following:


Since I am going to estimate it for several semiconductors I looked up for this one. It is very strange since I have to adjust all the time my load inductance by hand, otherwise it will look e.g. like following traces:


I just changed the load inductance to 10 µH! Seems quite strange for me.

With regards

 

[Alec_t]

The V3 and V4 voltages aren't specified in your schematic.

 

[teslaaa]

I found the mistake in my circuit. Thanks for the help.

 

[smithjones]

Hello everybody,
i am new here and I tried to estimate some losses in LTSpice using a DPT for several devices. However, I am not getting reliable results, since the voltage is just linearly increasing and my drain source voltage is not looking like expected. If there are some hints, where I have some mistakes, it is kindly appreciated! Attached there are the files.

Thanks in advance!
Best regards

Without seeing the schematic, the most common causes are missing or incorrect gate drive, no proper load or snubber, and incorrect device models or initial conditions. A linearly rising drain–source voltage usually means the switch is never fully turning on or off, often due to insufficient gate voltage, wrong reference for the gate driver, or a floating node. Double-check the gate drive amplitude and timing, ensure the source/emitter reference is correct, and verify that the DPT setup includes realistic parasitics and a proper load path.

 

[Sunnysky]

errors still exist in log after edits
ERROR: Node u1:x1:x_rs:m is floating and connected to current source u1:x1:x_rs:G1
ERROR: Node u1:x1:x_rd:m is floating and connected to current source u1:x1:x_rd:G1
ERROR: Node u2:x1:x_rs:m is floating and connected to current source u2:x1:x_rs:G1
ERROR: Node u2:x1:x_rd:m is floating and connected to current source u2:x1:x_rd:G1