In circuits with zero drain-source voltage turn-on (ZVS), this output capacitance energy is recycled to the load and/or input capacitance. When a FET turns off and voltage across it increases from near zero to its steady off-state voltage, energy is stored in the output capacitance. How is turn-off loss calculated for topologies with zero voltage turn-on (ZVS)? The power rating can therefore be thought of as output power. Power semiconductor efficiency in most systems is high enough to make the small error in power loss calculations from ignoring input versus output power negligible. Is this input or output power?įET-Jet Calculator makes no distinction between input and output power. Power rating is an input parameter for each topology. For this reason, the vast majority systems using SVM are 3-phase. Losses calculated with SPWM and alternating-nulls space vector modulation (SVM) are almost identical, but unlike SPWM, the switching of each phase with SVM is interdependent on the other phases. Although most systems are 3-phase, each phase is independent of the others with SPWM, and entering line-to-neutral voltage and then calculating line-to-line voltage allows support for any number of phases. Sine-triangle pulse width modulation (SPWM) is used to calculate power loss in AC/DC topologies. The AC/DC converters have line-to-neutral voltage as an input parameter. With SPWM, each phase is independent of the others, and therefore any number of phases is supported. Furthermore, SVM applies almost exclusively to 3-phase systems. However, only space vector can physically realize the 1.15x higher AC voltage with a given DC link voltage compared with SPWM. Both SPWM and SVM yield mathematically meaningful results with a modulation index up to. Overmodulation (pulse skipping) is not supported in Revision 1 of FET-Jet Calculator. In this case, the conduction and switching losses of SPWM versus SVM are almost identical, and it is practical to simply use SPWM for the loss calculations for both SPWM and SVM. There are many variations of SVM, but typically the time spent in each zero-state is balanced to minimize switching transitions and loss. What if I am using space vector modulation (SVM)? The AC/DC converters use sine-triangle pulse width modulation (SPWM). For surface mount on insulated metal substrate (IMS), please refer manufacturer’s data. If using a non-phase-change isolator pad, then a value of 1.8 ☌/W would be typical, but please refer data from the isolator material manufacturer. A value of 0.6 ☌/W is a conservative value for modern phase-change isolators. Many applications require electrical isolation between the conductive backside of the package and the heatsink. What value for Rthcs (isolator pad) should I use? Accuracy is quite sufficient for the intended purpose of FET-Jet Calculator, which is a power device selection and topology comparison tool for use early in a design cycle. FET-Jet Calculator balances these by minimizing sources of error wherever possible and making simplifications that allow quick results with little loss of accuracy for typical applications. There are tradeoffs between accuracy, ease of use, and speed.
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