# Zero Switching losses on synchronous boost **URL:** \ **Category:** PLECS\ **Tags:** thermal-model, switching-losses\ **Created:** [December 24, 2025, 8:56am UTC](https://forum.plexim.com/t/zero-switching-losses-on-synchronous-boost/2775 "2025-12-24T08:56:28Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![harazogo](https://avatars.discourse-cdn.com/v4/letter/h/b3f665/32.png) [@harazogo](https://forum.plexim.com/u/harazogo)\ **Post date:** [December 24, 2025, 8:56am UTC](https://forum.plexim.com/t/zero-switching-losses-on-synchronous-boost/2775/1 "2025-12-24T08:56:28Z")
Hello. I have simulated a synchronous boost converter with thermal model for mosfets AIMDQ75R011M2H (attached). I noticed that I have switching losses for the synchronous mosfet (in model: M2) only when it turns on. The turn-off switching losses are zero. I searched a bit in Plecs forum and followed your advice to mirror the look-up tables for negative current values, but I get the same results ( [Switching losses - MOSFET, negative current](https://forum.plexim.com/t/switching-losses-mosfet-negative-current/464) ). Also, if I add dead-time (1-2% of Tsw), switching losses do not change either. In forum, I also found that: “For turn-on loss, PLECS looks at the voltage directly before the switching event and the current directly after. For turn-off loss, PLECS looks at the voltage directly after the switching event and the current directly before.” Is it possible for me to check which values Plecs takes into account around switching, in order to calculate the losses? Is there anything else that I should take into account for calculating switching losses? Thank you in advance, Hara [Synchronous\_Boost\_losses.plecs](https://forum.plexim.com/uploads/short-url/8bUfwtjRJXTAhyHLQC4aqSayku4.plecs) (54.2 KB) ---
**Author:** ![harazogo](https://avatars.discourse-cdn.com/v4/letter/h/b3f665/32.png) [@harazogo](https://forum.plexim.com/u/harazogo)\ **Post date:** [December 24, 2025, 8:57am UTC](https://forum.plexim.com/t/zero-switching-losses-on-synchronous-boost/2775/2 "2025-12-24T08:57:11Z")
Here is the xml for mosfet as well. [AIMDQ75R011M2H-plecs.xml](https://forum.plexim.com/uploads/short-url/acgDDjthwNj8gnUXGN73HlCEQoG.xml) (22.8 KB) ---
**Author:** ![RetoChristen](https://dub1.discourse-cdn.com/flex006/user_avatar/forum.plexim.com/retochristen/32/1225_2.png) [@RetoChristen](https://forum.plexim.com/u/RetoChristen)\ **Post date:** [December 24, 2025, 1:42pm UTC](https://forum.plexim.com/t/zero-switching-losses-on-synchronous-boost/2775/3 "2025-12-24T13:42:36Z")
Hi Hara, first of all, I want to point out that the thermal description is not optimally defined for switching losses. In particular, it is important that the switching losses at 0 A and 0 V are explicitly defined as 0 J in order to avoid incorrect interpolation. I have added this condition to the thermal descriptions. > “For turn-on loss, PLECS looks at the voltage directly before the switching event and the current directly after. For turn-off loss, PLECS looks at the voltage directly after the switching event and the current directly before.” This behavior can best be verified by probing the MOSFET **M2** and inspecting its signals. In the added **Scope6** , you can see all the relevant waveforms required to pinpoint the loss calculation. In this specific case, the situation is a bit tricky because the thermal description not only includes a lookup table, but also an additional equation. If you change the **Computation method** from _Lookup table and formula_ to _Lookup table_, you will notice that no switching losses occur. The reason is that only negative currents are present, and therefore no switching losses are generated. In this operating condition, the body diode starts conducting and the MOSFET channel can turn on and off under ZVS conditions. You can verify this by disconnecting the gate signal, only the diode will then conduct. While conduction losses increase significantly, there are still no switching losses. If you switch the **Computation method** back to _Lookup table and formula_, you will see that turn-off losses become non-zero. This is caused by the additional term `+lookup('Eoss', v, T)` that is added to the **Turn-on loss** formula. For **Turn-off loss** , the same term is subtracted, but the overall formulation ensures that no negative loss values occur. The explanation for this additional term can be found in the **Comment** section provided by Infineon: > Since electrical measurements overestimate the Eoff losses, > we correct this behavior by transferring the Eoss-related > energy to the respective turn-on energies. > > Qrr is not modelled explicitly – it is implicitly included in the energy values. For this application, it may therefore make more sense to explicitly model the reverse-recovery losses of the body diode, as explained in this forum post: > [@Diode reverse recovery loss modelling using the MOSFET-with-diode component](https://forum.plexim.com/t/diode-reverse-recovery-loss-modelling-using-the-mosfet-with-diode-component/1796): > > I’m trying to create the loss model of a MOSFET power module and would like to use the MOSFET-with-diode component from the PLECS library instead of using a separate MOSFET and a diode. I found a way to input the diode and MOSFET conduction loss data into separate tabs by enabling gate dependent conduction losses (which is not intuitive to discover, by the way), but I can’t find a way to enter the reverse recovery losses of the body diode. There are tabs to enter the turn-on and off … I hope this helps. [AIMDQ75R011M2H-plecs\_RC.xml](https://forum.plexim.com/uploads/short-url/jlAXKasEJ3ITZYXA2j7sEDAfGc3.xml) (23.0 KB) [Synchronous\_Boost\_losses\_RC.plecs](https://forum.plexim.com/uploads/short-url/5jIbhIyzefiUSlOePWsHRsoIPRu.plecs) (59.4 KB)