Modeling Switching Losses and Efficiency

Date

Previously Held on September 14th, 2017

This one hour webinar will explore measuring switching losses and efficiency on SIMPLIS circuits. In order to effectively model switching losses, the MOSFET driver circuit must be modeled with more detail than is typical. The driver sourcing and sinking current limits, as well as the saturation resistances, must be realistically modeled for the switching losses to approximate a real circuit. 

Once the driver is accurately modeled, the MOSFETs must be considered, and the non-linear capacitance characteristics understood. Once the combination of an accurate MOSFET model and the driver for the MOSFET is complete, an accurate simulation of the switching losses and the power supply efficiency can be made.

Link to Webinar Recordings

The webinar recording can be viewed at this link: Modeling Switching Losses and Efficiency (54:42)

Abstract

  • Part I: Estimating Switch Losses
    • Accuracy
    • Modeling MOSFET Losses
    • Modeling Nonlinear Source and Sink Current of Driver
  • Part II: Measuring Efficiency
    • Efficiency Calculator
    • DVM automated measurements and reporting

Reference Materials

Schematics and presentation slides for the webinar can be downloaded here: ModelingSwitchLosses_Efficiencty.Sept2017.zip

Questions and Answers

Q1: If my switch and driver models are subcircuits of my IC model, and the circuit is flattened to an ASCII netlist, how can I measure efficiency with power probes?

A1: The power probes work on any subcircuit, including .sxcmp files. So a power probe placed on the IC model symbol will reflect the overall loss of the IC model. Unfortunately, once the circuit is flattened, there is no way to break out the individual power losses of the subcircuit using our tools.

Q2: Why can't we use CV squared for switching loss estimation?

A2: The MOSFET capacitance in non linear, so this method will introduce a large error. You can integrate the capacitance over the voltage swing to get the charge and this will be accurate. This is effectively how SIMPLIS works - nonlinear capacitors are defined on the Charge vs. Voltage plane. This results in an accurate estimation of the switching losses.