Spectrum Software
Industrial Strength Simulation




Spectrum Software has released Micro-Cap 11, the eleventh generation of our SPICE circuit simulator.

For users of previous Micro-Cap versions, check out the new features available in the latest version. For those of you who are new to Micro-Cap, take our features tour to see what Micro-Cap has to offer.




How to Model a Zener Diode


Modeling zener diodes is not much more complicated than modeling LEDs. As with LEDs, modeling is done using the diode primitive and the primary objective is to match the reverse characteristic. To model a zener diode, set the diode model parameters to the indicated data sheet values.

To model a zener diode, set the diode model parameters to the indicated data sheet values.

Model ParametersData Sheet Values
TBV1(TC in mV/C)/(BV*1000)
To simplify the process, consider the following test circuit.
Zener Test Circuit
This circuit, when run in DC analysis with the analysis limits shown below, plots the diode's reverse current vs. the reverse voltage, stepping the value of temperature from 0 to 127 in steps of 50 degrees.

Zener Analysis Limits

The figure below shows what the DC analysis looks like for the MMSZ5221BT1 zener.

Zener Analysis Limits
Note that Micro-Cap 6 adjusts the saturation current parameter, IS, to match the BV, IBV point exactly by taking into account the RS value.

For example, the RS of 30 in this case produces an additional drop when the diode current is at the IBV value of 20ma of 600mv, which, without compensation, would push the BV at 20ma to 2.4 + 600mv = 3.0 volts.

You can also add the CJO parameter from the C vs. nominal zener voltage curves, if they are given in the data sheet. Use the 0 volt bias curves.
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