Reverse Recovery of a Power Diode : Reverse Recovery of a Power Diode

Requires: S-Pisces/MixedMode
Minimum Versions: Atlas 5.22.1.R

This example demonstrates the reverse recovery of a silicon power diode. It shows:

  • Structure definition using Atlas
  • The SPICE-like command syntax for simulating MixedMode circuits
  • Steady state and transient analysis of a power diode

The structure consists of a rectangular silicon power diode. Atlas is used to define the power diode structure including mesh, materials, electrodes, and doping. The mesh rect statement defines a rectangular mesh with grid lines at the locations specified by the x.m and y.m statements. The entire mesh is defined as one silicon region using the region statement. Electrodes are defined on top and bottom and the doping statement is used to define a uniform background concentration and gaussian n-type and p-type regions. This structure is saved and will be used as a device by MixedMode.

In this simulation, the MixedMode circuit simulator uses Atlas to calculate the electrical characteristics of the power diode under the specified circuit conditions. First, a steady-state simulation of the power diode circuit is performed.

The .begin and .end statements indicate the beginning and end of the MixedMode syntax. The MixedMode commands are similar to those used in SmartSpice. Circuit components, topology, and analysis are defined within. In general, the circuit component definition consists of three parts: the type of component, the lead or terminal node assignments, and the component value or model name. For example, the first component definition in this simulation is a dc voltage source. v1 defines the component as voltage source number one, 1 and 0 are the two circuit nodes for this component, and 1000 indicates that the voltage source value is 1000 volts. The remaining circuit components are resistors r1 r2 , inductor l1 and independent current source i1 . The adiode statement specifies a device to be analyzed by Atlas. The a part of the adiode command specifies that this is a device statement. The diode portion simply defines the device name. The option infile= indicates which device structure file is to be used. The .nodeset statement defines the initial values for node voltages and the .save outfile= statement saves the result to the indicated file. Since this is the steady state solution, no output log data file is needed. Additionally, the .options command sets the solution method to a modified two-level Newton using the m2ln parameter. Other command line options exist. Please refer to the MixedMode section of the Atlas user's manual for a complete list.

To completely specify the simulation, the physical models used by Atlas must be specified. The model statement is used to turn on the appropriate transport models. This set includes conmob: the concentration dependent mobility model, fldmob: the lateral electric field-dependent mobility model, consrh: Shockley-Read-Hall recombination using concentration dependent lifetimes, auger: recombination accounting for high level injection effects, and bgn: band gap narrowing. Refer to the Atlas user's manual for a description of these models. The material statement is used to override default material parameters. In this case, the carrier recombination fixed lifetimes are set. Finally, an impact ionization model is enabled using the impact statement with the selb option. This specifies that the Selberherr impact ionization model is to be used.

The next step is the transient analysis which is specified in a similar manner. The reverse recovery of the diode is simulated by dropping the value of output resistor r2 over a small increment of time. The r2 statement contains additional syntax to perform this task. Here, the resistor is treated as a source whose resistance decreases exponentially from 1 MOhm to 1 mOhm over the specified time step. This action essentially shorts out the parallel current source i1 which is also connected to the base of the diode. The .trans statement is used to specify the time stepping parameters for the transient analysis. In addition, the .log statement saves the diode output characteristics over the time interval specified. TonyPlot plots the transient reverse recovery of the power diode.

To load and run this example, select the Load example button in DeckBuild. This will copy the input file and any support files to your current working directory. Select the run button to execute the example.