New Feature Released Today: Plot True Dissipation

Today’s release of QSPICE includes the ability to plot dissipation in devices. It’s implemented for resistors, capacitors, inductors, diodes, MOS level 1, VDMOS, and MOS level 2010; i.e., everything you need to model power devices.

This is actual dissipation in the device, not energy flow into the component, e.g., the power dissipated in the series and parallel losses of reactances. For the semiconductors, the device equations are fully replumbed to report only real current through real voltage, not current contributing to energy stored in the devices’ reactances. All the displacement currents are still in the simulation, but they don’t contribute to heating and aren’t added to the reported dissipation.

It’s off by default becuase it’s new and there’s a fair bit of compute overhead. To turn it on, add the SPICE directive

.options savepowers=1

Ctrl-Left click on a device to plot dissipation. Ctrl-right click on a plot label to average.



Is there an intention to add this function to BJTs? Thanks.

Yes it’s intended, but not scheduled. It involves rethinking the entire device evaluation – separating real and displacement currents through pages of scientific floating point math. It’s what I do for a living but it takes a couple days dedicated work.

In the past, I just summed the integrated Poynting vector over all ports. That was easy, but not really what is wanted or nearly perfectly correct. It’s a situation that exposes how pretty good and perfect are in fact enemies.


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