# How to create an LTspice model for 1N4733A Zener Diode?

I'm new to LTspice. I'm using EveryCircuit as a crutch and would like to run my circuit simulation in LTspice to compare simulation results.

I've built a basic circuit to understand how a zener diode works. The physical zener diode I have hooked up is an (obsolete) 1N4733 glass-packaged zener diode. The circuit I'm working with is:

In my experiment, I've flipped the direction of the z-diode to see what happens:

I can't find an LTspice model for the 1N4733 but have found what appears to be parameters for a zener diode that you'd put into a SPICE directive:

.model D1N4733  D(Is=1.214f Rs=1.078 Ikf=0 N=1 Xti=3 Eg=1.11
+ Cjo=185p M=.3509 Vj=.75 Fc=.5 Isr=2.601n Nr=2 Bv=5.1 Ibv=.70507
+ Nbv=.74348 Ibvl=4.8274m Nbvl=6.7393 Tbv1=176.471u)


And the transient simulation results:

You can see that the LTspice simulation result doesn't match that of EveryCircuit's nor what was measured on the o-scope. The zener voltage is ~5V and in the forward-bias orientation, I expected the Vn002 to clip at -5V. The SPICE directive must be incorrect.

Problem is, those parameters and their values are gobbly gook to me. What do they mean? Which one represents the zener voltage value?

Solution

First, your diode should be reversed, since it's a Zener. Then you have to rename it to reflect the model that you just pasted in the schematic: rename D to D1N4733 (that is the name that follows .subckt). And last, if all you need is to use the diode then there's no need to worry about the parameters -- they're simply passed to the intrinsic model of the diode in order to behave like a real one, or at least as well as the model is. So, you can ignore them, unless you want to know the details, in which case you should be searching for tutorials for SPICE.
• @MinhTran Best place to start is the built-in Help. Either press F1 or in the Menu Bar: Help -> Help Topics. Look for D. Diode in there. If you want to get into the equations and theory for what those parameters do, then I really like this book: amazon.com/dp/0070024693 Commented Dec 7, 2020 at 2:21