Diode with Reverse Recovery.

The dynamic model for the diode is based on Spice parameters. A great advantage compared to the original Spice model is that the dynamic diode model called DiodeReverseRecovery can also simulate reverse recovery.
The model for the diode exhibits reverse recovery based on various sets of parameters. It can either be based on Spice parameters, physical quantities or measured data. The reverse recovery diode model is found in components/library/Semiconductor/Diode.

Static characteristic
The static V-I characteristic is based on spice parameters and forms the basis for the static curve of the dynamic diode model.

I_d=I_s(e^{q · Ud / N ·k ·T}-1) where

• q=1.6e-19
• k=1.38e-23

This equation is approximated with the internal Caspoc Diode model that is also temperature dependent. The constant value for R_S is added to the on-resistance calculated from the above equation and the total R_on is made dependent on temperature as indicated in the Power Electronics Handbook by the following relation:
R_on(T) =R_on · (T/300)^2.3. Here T is the junction temperature in degrees Kelvin. The on-resistance of the diode, models the losses during the conduction of the diode.

Dynamics
The junction capacitance C_j0 is constant in this model. In the original spice model this capacitance is non-linear to model reverse recovery, but since this model includes a new mechanism for modeling the reverse recovery, the junction capacitance is kept constant. The reverse recovery is modeled based on various parameters which are outlined in the next section.

Reverse Recovery
The reverse recovery in the DiodeReverseRecovery model is based on stored charge during the conduction interval. Dependent on the way the diode is forced to turn-off, the reverse recovery current is provided by the stored charge in the diode. This can be modeled and parameterized in various ways:

• Spice parameter based
• Physical parameter based
• Measured data based

Each method predicts the reverse recovery current during turn-off. Depending on the parameters provided, the model is parameterized. Leaving the remain parameters equal to zero, cancels them.

• Spice parameter based The original spice parameters are not that bad. The only problem is the model, that was originally designed for small signal diodes. However the parameter TT, modeling the transit time, can be used to model the reverse recovery behavior.
  The parameter TT can apprximately be choosen as TT=40ns for a diode with a blocking voltage of 100V, to TT=4us for a diode capable of blocking 1000Volt. If TT is set to zero the transit time is approximated from the reverse breakdown voltage BV.
• Physical parameter based The forward storage time in the diode is modeled by the parameter TT, modeling the transit time. The parameter is the same as in the original spice specification, so it can be used to model the reverse recovery behavior.
  The parameter TT can approximately be choosen as TT=40ns for a diode with a blocking voltage of 100V, to TT=4us for a diode capable of blocking 1000Volt. If TT is set to zero the transit time is approximated from the reverse breakdown voltage BV.
  The time constant with which the reverse recovery is ending is specified by the parameter τ_rr. If τ_rr (tau_rr)=0, the diode snaps off very fast. A value greater than zero defines the time constant by which the reverse recovery current decays from I_RR towards zero.
• Measured data based If measured data is available, the parameters I_F, dI_F/dt, Q_RR and T_RR can be specified.
  

  IF	The maximum forward current during the conduction of the diode. During conduction the total amount of scharge is depending on this value.
  dIF/dt	The gradient of the diode current during turn of, measured at the zero crossing of the diode current. This value is depending on the load circuit connected to the diode and the parasitic inductance in series with the diode.
  QRR	The reverse recovered charge is taken from the specification in the data sheet and is specified for a typical forward current IF and turn off gradient dIF/dt of the forward current
  TRR	The reverse recovery time is taken from the specification in the data sheet and is specified for a typical forward current IF and turn off gradient dIF/dt of the forward current

  In the datasheet the parameters Q_RR and T_RR are specified for a typical measurement, where I_F and dI_F/dt are the test circuit conditions.

To model the reverse recovery correctly, the step size dt for the simulation should be choosen such small, that the reverse recovery can be simulated in detail. This requires a small value of the step size dt, which leads to longer simulation times. However it will show the transients that will occur during the turn off of the diode and any unwanted effects due to a possible high reverse recovery current. Also the effects of the parasitic components surrounding the diode can be studied in more detail.

Losses and Thermal simulation
The diode model has a thermal connection that has to be connected to a heat sink model. The temperature rise due to the conduction and reverse recovery losses is modeled on this connnection. A heat sink is build from the components found in components/library/Heatsink The parameter R_th and C_th model the thermal model form junction to case. The initial temperature of the junction is modeled by the parameter InitialTemp. If a more detailed thermal model for the junction to case thermal path has to be build, R_th and C_th simply model the first chip-layer and the following layers are modeled by subsequent thermal models.

The parameter for the diode are summarized in the following table. For the parameters that are compatible with the spice diode model the column Spice shows the spice parameter name. Parameters that do not exist in the spice model are indicated with a N.A. Default values for the parameters are given.

Parameter	Default	Spice	Function
IS	10-14	IS	Saturation current.
BV	106	BV	Reverse breakdown "knee" voltage.
N	1.5	N	Emission coeficient.
TT	0	TT	Forward Storage Time (Transit Time).
Cj0	50pF	CJ0	Junction capacitance.
RS	1mOhm	RS	On resistance.
τrr (tau_rr)	0	N.A.	Decay time constant of the reverse recovery current after IRR. If this value is set to zero, the diode has a snappy recovery.
Rth	1	N.A.	Thermal junction-case resistance.
Cth	0.5m	N.A.	Thermal junction-case capacitance.
InitialTemp	25	N.A.	Initial junction temperature.
IF	0	N.A.	Measured maximum forward current.
dIF/dt	0	N.A.	Measured current gradient during turn off. (Measure at the zero-crossing)
QRR	0	N.A.	Measured reverse recovery charge.
TRR	0	N.A.	Measured reverse recovery time.