SIMPLIS Diode Models

Any SPICE diode model installed in the SIMetrix library can be converted for use in SIMPLIS. When a diode is placed on a SIMPLIS schematic, a model parameter extraction routine is invoked to automatically convert the SPICE model to a SIMPLIS model. During the model parameter extraction process, SIMetrix/SIMPLIS automatically runs several SPICE simulations on the SPICE model and extracts the SIMPLIS model parameters. After the Piecewise Linear (PWL) model parameters have been extracted, the resulting diode model will run in SIMPLIS. Any installed SPICE diode model can be used in SIMPLIS.

The extracted diode model can then be used to create a model for one of four diode configurations:

Configuration Description Additional Parameter
Single A single diode none
Parallel Multiple diodes in parallel Number of parallel diodes
Series Multiple diodes in series Number of series diodes
Bridge Four diodes in a bridge configuration Bridge imbalance voltage

These diode configurations are more than a convenience, SIMPLIS will run faster with these models, and run into less problems with errors.

In this topic:

Extracting the Diode Parameters

When you place a Diode symbol on a schematic, the Extract Diode Parameters dialog opens for you to edit the default test conditions. The default test conditions are defined using the command shell menu File > Options > SIMPLIS Options... . For additional information, see SIMPLIS Diode Options.

The following table describes the Extract Diode Parameters dialog test conditions.

Extracted Diode Model

Test Condition Default Value Units Description
SPICE Model D1N4148   The SPICE model used to extract SIMPLIS parameters.
Model type Extracted   Invokes the model parameter extraction algorithms.
Forward current 200m A The peak forward current used for curve fitting. The algorithm fits a straight line between 50% and 100% of this value.
Reverse voltage 100 V The peak off-state voltage seen by this device. Used to extract capacitance for model level = 1 which includes parasitic capacitance. Breakdown is not modeled.
Model temperature 50 °C Temperature used for all extraction simulations.
Model level 0   Model complexity. For information on choosing the model level, see SIMPLIS_Diode_Model_Levels.
Number of Segments 3   Diodes may have two segments - representing On and Off Resistance or three segments with the third segment representing the transition between the On and Off states.
Initial Condition 0 Reversed Biased Sets initial conducting segment.
Limit maximum off resistance Checked none Limits the off resistance for the diode. For some SPICE models, this will produce a SIMPLIS model which runs faster.
Maximum off resistance 100Meg W The maximum off resistance of the diode. This value is used only if the "Limit maximum off resistance" checkbox is Checked.

Show extracted PWL waveforms option

Beginning in version 8.2, there is now an option to plot the extracted parameters as a set of PWL curves. To enable this option, select the Show extracted PWL waveforms checkbox and extract the model. After the model is extracted, a set of curves will be generated comparing the extracted PWL curves against the simulated SPICE curves. The curves displayed will depend on the model level being extracted.

Below is a typical PWL approximation of the Forward Bias Current characteristic of the diode, with the SPICE curve in red and the PWL curve in blue.

SIMPLIS Diode Model Levels

The SIMPLIS Diode models support two levels: 0 and 1.

  • Level 0 is a pure conduction diode.
  • Level 1 adds the junction capacitance.

SIMPLIS extracts a model based on the model level chosen in the Extract Diode Parameters dialog. Although these models are internally saved as ASCII text, the following illustrations show the two model levels in a schematic form.

Level 0 Model

Level 0 models a diode on/off resistance values only. This Level 0 model can be used  for almost every simulation you may encounter in SIMPLIS.

  • The diode conduction region is modeled with a 2- or 3-segment resistor.
  • There is no junction capacitance in a Level 0 model.

Below is a schematic view of Level 0 model:

Level 0 models these circuit elements Level 0 Schematic
!R_D_POWER: Diode modeled by PWL Resistor

Level 1 Model

Level 1 models a diode with on/off resistance values and a junction capacitance with up to 4 PWL segments.

  • The diode conduction region is modeled with a 2- or 3-segment resistor.
  • The junctions capacitance is modeled with a variable number of segments, with a maximum of four.

Below is a schematic view of Level 1 model:

Level 1 models these circuit elements Level 1 Schematic
!R_D_POWER: Diode modeled by PWL Resistor
CJ: Junction Capacitance modeled by PWL capacitor
 

User-defined Models

The user-defined model uses parameters entered directly in the Edit Diode Parameters dialog without invoking the model extraction algorithms. A Diode can be switched from an extracted model to a user-defined model at any point; however the extracted parameters are by default copied over to the user-defined parameters, replacing any user-entered values. You can disable this behavior in the SIMPLIS Options by clearing the check box labeled Automatically copy extracted parameters to User-defined parameter. You can access these options from the command shell menu File > Options > SIMPLIS Options... . For more information, see SIMPLIS Diode Options.

User-defined Diode Model

Parameters Default Value Units Description
Label: USER_LABEL    
Model type: User-defined    
Forward voltage: 750m V Diode forward voltage drop. The diode effectively turns on at this voltage.
Forward resistance: 10m The diode resistance at voltages higher than the Forward voltage.
Off Resistance: 1G The resistance of the diode at voltages less  than the Forward voltage.
Output Capacitance: 0 F Linear capacitance at the Reverse voltage

User-defined model

Models these circuit elements User-defined Schematic
!R_D_POWER: Diode modeled by PWL Resistor
CJ: Junction Capacitance modeled by a linear capacitor

Manually Generate and Customize Diode Models

You can customize or manually generate your own diode models using a parameter string with multiple PARAM_NAME=PARAM_VALUE key-value pairs. The parameter names and their functions are described in the Diode Model Parameters section below. You can interpret the SIMPLIS parameter values from device datasheet specifications and curves.

You can compose the parameter string in a text editor, spreadsheet, or script. The order of the parameter names in the parameter string and the capitalization of the parameter names are irrelevant.

You can include a PROTECTED=1 key-value pair to prevent from extracting a model and overwriting your manually generated parameters. The PROTECTED=1 key-value pair is not used in the simulation.  

Note: When you click on the device after adding the PROTECTED=1 key-value pair, the following message box appears to warn you that this is a hand-edited model.

To customize or generate your own diode model, follow these steps:

  1. Create a parameter string of multiple PARAM_NAME=PARAM_VALUE key-value pairs using your preferred text editor, spreadsheet or script.
  2. Add the PROTECTED=1 key-value pair to the parameter string.
  3. Extract a diode model and place it on a schematic.
  4. Right click on the symbol and select Edit/Add Properties....
  5. Double click on the PARAM_VALUES property.
    Result: The Edit Property dialog opens. At this point, you can change individual parameters in the Value box, or replace the entire default properties with the parameter string that you created in Step 2.
  6. To replace the entire string, follow these steps:
    1. Click in the Value box and type Ctrl A to select all of the existing parameter string, and press Delete.
    2. Copy the parameter string you completed in Step 2 and paste into the Value box.
    3. Click Ok.
  7. To change the name of your customized model, double click the VALUE property in the Edit Properties dialog, and change the name in the Value box.
  8. To return to the schematic, click Ok.
Alternately you can write the PARAM_VALUES property to the symbol using the Prop command in the command line with the following syntax:  
prop PARAM_VALUES parameter_string
where parameter_string is the set of key-value pairs that you created in Steps 1 and 2 above.
Important: Since parameter_string contains spaces, the entire string must be enclosed in double quotes.

Diode Model Parameters

The following tables detail the parameters which define the electrical behavior of the Diode model. Several other parameters in the PARAM_VALUES property have no effect on the electrical behavior of the model. These parameters are used to populate the Extract Diode Parameters dialog box.

Note: The default values are unlikely to appear in an extracted model. If these parameter values appear in your design, there has been an error in composing the parameter string.

Conduction Model

Diodes are modeled in SIMPLIS with Piecewise Linear (PWL) resistors. The PWL segments are represented by X,Y points

  • The points are defined with the voltage on the X-axis and  the current on the Y-axis.
  • The resistance is the inverse of the slope of any segment.
  • The subscripts on IDx and VDx indicate the point pair location from lowest voltage, i.e.  reverse biased, to highest voltage, i.e. forward conduction.

Conduction Parameters

Parameter Names Default Value Description
NUMSEG   3 Number of segments in the diode model.
  • Valid NUMSEG are 2 , 3, 4, 5, 6
VD0 ID0 1.123456789 X-Y point definitions for diode:
  • X-axis is the Anode-Cathode voltage  in volts (V).
  • Y-axis is the Diode forward current in Amps (A).
  • Points with subscripts greater than the NUMSEG parameter are ignored.
VD1 ID1 1.123456789
VD2 ID2 1.123456789
VD3 ID3 1.123456789
VD4 ID4 1.123456789
VD5 ID5 1.123456789
VD6 ID6 1.123456789

Capacitor Model

Capacitors are modeled in SIMPLIS with Piece-Wise Linear capacitors.

  • The same system of point-pairs is used,but the plane is defined with Voltage on the X-axis and Charge  on the X-axis.
  • The same system of subscripts is used to define the point pairs.
  • VCJ0 and QCJ0 represent the lowest Voltage-Charge pair, with increasing subscripts representing  increasing reverse bias.
  • On the Voltage-Charge plane, capacitance is the slope of any segment.

Junction Capacitance Parameters (LEVEL=1 Only)

Parameter Names Default Value Description
CJ_NSEG   4 Number of segments in the Junction capacitor model
VCJ0 QCJ0 1.123456789 X-Y point definitions for Junction capacitor:
  • X-axis is Cathode-to-Anode voltage in volts (V).
  • Y-axis is charge in coulombs (C).
  • Points with subscripts greater than the CJ_NSEG parameter are ignored.
VCJ1 QCJ1 1.123456789
VCJ2 QCJ2 1.123456789
VCJ3 QCJ3 1.123456789
VCJ4 QCJ4 1.123456789
VCJ5 QCJ5 1.123456789
VCJ6 QCJ6 1.123456789
VCJ7 QCJ7 1.123456789
VCJ8 QCJ8 1.123456789
VCJ9 QCJ9 1.123456789
VCJ10 QCJ10 1.123456789

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