Diode Modeling

Diode Modeling Statement

DR. SPICE diode model parameters cover all diode types, but you may not need to use them. For many applications, the default statement generates the desired model.

The default statement for a diode is:

.DATASHEET <DEVICE NAME> DIODE

The statement format for a diode with parameters is:

.DATASHEET <DEVICE NAME> DIODE <PARAMETERS>

Use parameters to specify the following diode characteristics:

Forward conduction characteristics
Diode capacitances
Reverse breakdown characteristics
Transit time as a function of reverse recovery time

Forward Conduction Parameters

These parameters generate the forward conduction characteristics based on the forward current vs. forward voltage graph. If you do not have this graph, omit these parameters.

Forward Conduction Parameters

*Parameter*	*Description*
if1	A low value of forward current
if2	A value of forward current that is in the exponential portion of the curve
if3	A high value of forward current, measured on a portion of the curve where the current is clearly limited by the parasitic resistance of the device
vf1	The voltage at which if1 is measured
vf2	The voltage at which if2 is measured
vf3	The voltage at which if3 is measured

Diode Capacitance Parameters

These parameters generate the diode capacitances based on a graph of junction capacitance vs. reverse voltage. Note that voltages should be entered as positive numbers. If you do not have this graph, omit these parameters.

Diode Capacitance Parameters

Parameter	Description
cj1	A value of the diode capacitance measured at a low reverse voltage.
cj2	A value of the diode capacitance measured at a high reverse voltage.
vcj1	The voltage at which cj1 was measured.
vcj2	The voltage at which cj2 was measured.

Reverse Breakdown Parameters

These parameters are most important for zener diodes, but you should include reverse breakdown voltage if there is any possibility that your circuit will exceed the reverse breakdown voltage across the diode.

Reverse Breakdown Parameters

Parameter	Description
iz	Zener current, or the current at reverse breakdown iz.
vz	Zener voltage, or the reverse breakdown voltage bv.
zz	Zener impedance.

Transit Time Parameter

This parameter calculates the transit time tt, as a function of the reverse recovery time Trr. This parameter is usually only important in switching circuits.

trr - Reverse recovery time, measured at Ir=If

Diode Modeling Example

The following .DATASHEET statement generates a model of a 1n5827 diode:

.DATASHEET d1n5827 DIODE
+ if1=0.2 vf1=.21 if2=15 vf2=.4 if3=100 vf3=0.8
+ cj1=2e-9 vcj1=70e-3 cj2=600e-12 vcj2=7
+ vz=100 iz=1e-3

The Model Maker output file for this example (d1n5827.mod) is as follows:

.MODEL d1n5827 D ( IS = 6.21191e-05 bv = 0.001
+m = 0.536018 cjo = 2.09798e-09 rs = 0.0032 tt = 1.4e-12)

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