run the simulation of a simple halfbridge circuit,however the upper switching loss is abnormal, it seem there is 0, but that’s not correct, the same set up for the pair of switch, the lower switching loss may seem correct
Hi Lok,
It would be helpful if you could share your model so we can take a closer look at what is happening.
eee.plecs (110.8 KB)
thank you for the reply, the thermal model i used the wolfspeed model
Hi Lok,
Thanks for providing the model. The issue you are running into is the following:
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Due to dead-time, the blocking voltage across Q3 is already 0 V by the time the turn-on gate signal arrives. The PLECS thermal model evaluates switching losses at the turn-on instant by looking at the blocking voltage immediately before turn-on and the conducting current immediately after turn-on. In your case, during the dead-time, the inductor current forces the body diode of Q3 to conduct. As a result, the blocking voltage is 0 V at the moment of turn-on. Therefore, the lookup table returns 0 J of switching energy loss for Q3.
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Q4 does not experience this behavior. In your model, the current through the lower switch appears to always flow from drain to source. During dead-time, the body diode of Q3 conducts, and Q4 only turns on when its gate signal goes high. As a result, the PLECS thermal model sees approximately 600 V of blocking voltage right before turn-on and about 5 A of conducting current immediately after turn-on. This leads to roughly 45 µJ of switching energy loss based on the lookup table.
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Another source of difference is conduction loss. The body diode is relatively lossy, so during dead-time the conduction losses of Q3 are higher due to body diode conduction. Although the duty cycle of diode conduction is relatively small, it is still something to be aware of. This does not occur for Q4, since its body diode never conducts in your operating condition because the current through Q4 remains positive.
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Finally, looking at the datasheet for the Wolfspeed C3M0045065J1 device that I downloaded in November 2025, the conduction losses are not perfectly symmetrical. Around the current levels seen in your model, approximately 5 A, the forward Ids conduction losses are slightly higher than the reverse Ids conduction losses. This asymmetry will also contribute to the differences you are observing.
Overall, the primary contributor to the discrepancy you are observing is that Q3 experiences essentially zero switching loss, while Q4 incurs both turn-on and turn-off switching losses.
Hope this helps!
thanks for the reply, but the turn on energy is zero is understandable cause the soft switching of the sychronous boost. the strange point is the turn off energy is also zero according to the scope shown in the figure. i mean the turn off energy should not be zero, but the simulation shows that only conduction loss is occured in the q3
thank you for your comment, you are right , so are there any solution to deal with it, we all know that the turn off energy is existing
hi lok,
What I mentioned earlier isn’t accurate, and I’ve removed it from this thread to avoid confusion. What is happening is the high-side switch at turn off has positive blocking voltage right after turn off and NEGATIVE conducting current right before turn off. In the thermal description for C3M0045065J1 the losses for this condition is zero and thus you are not seeing any turn-off switching losses.
In your setup, the high-side switch will effectively experience diode reverse recovery, which is typically modeled as a loss by extending the switching loss calculation to include positive blocking voltage and negative conducting current. Please see Diode reverse recovery loss modelling using the MOSFET-with-diode component - #2 by Bryan_Lieblick .
To obtain accurate results, you will need to contact the Wolfspeed applications team to determine whether they can provide the necessary reverse recovery data for your device.
Hope this helps and sorry about the confusion.
thank you very much, to my understanding, plecs simulation is right about the high-side switch turn on switching loss and the turn off switching loss, the loss should be zero since the body diode conduct(there are a little loss in reality but can omitted) . however, the reverse recovery energy of the body diode is missing during the low-side switch turn on, that’s the problem, am i right?
Yes, the high-side switch body diode reverse recovery, which in PLECS can be modeled in the thermal domain as a switching loss, is not included in the Wolfspeed thermal model.
As a result, in your simulation the reverse recovery of the high-side body diode during low-side turn-on is effectively being treated as an ideal diode, meaning no reverse recovery losses are accounted for.
thank you very much!!!