Hi all,

I'm writing since I need to simulate on Spice the breakdown effect of avalanche BJT transistors. Now, the Gummel-poon model does not describe this phenomenon, so I came across several options. The first one is the VBIC model, which should be supported by LTspice, but it is hard (if not even impossible) to find some models around. I also wrote to Diodes Inc. to ask for VBIC models of some of their avalanche BJT, but I never got a reply.
The same is for the Mextram BJT model.

Now, I recently came across the @Bordodynov outstanding LTspice library, and I found some avalanche BJT models fully working in the breakdown region!
Since I need it for a High voltage pulser, I have to use some BJT with higher BV voltage, such as ZXT415 or FMMT417, and I'd like to ask @Bordodynov some additional information on how you modeled this effect in the example transistors you included in your library. Do you have some references? how can I replicate this model for those BJT I mentioned? Do I need some experimental data? thank you so much in advance!

 

I complemented the standard transistor model by including the effects of carrier avalanche propagation using Miller's formula. I also made available examples in addition to the element library. This is in the example.zip file. The transistors you mentioned are in my library.

 

Thank you @Bordodynov, for your quick reply.

Indeed, I looked into the examples->npnavalanche, but I can see only examples for 2N2369, KT315 (that should be a replacement for 2N3904), KT342 ( I found only a Russian datasheet, but unfortunately, I'm not able to read it) and MBBT2369.



Looking in to the [ZZZ] library, under 'Avalanche' there are the ZTX413 and ZTX415, and FMMT417, but it seems to me they are standard models.

 

and ZTX415, and FMMT417:

 

Dear @Bordodynov , yes, I found the ZTX413 model in the [Avalanche] folder, but I guess it is not the modified SGP model with avalanche multiplication.



Here, on the left there is one of your examples of 2N2369A avalanche. On the right, I replicated the schematic with the ZTX413 model from the avalanche library. You can see on the ZTX413, once the BV is reached, the voltage is somehow truncated and the current folwing into the 50 Ohm load doesn't overcome the 100 uA value. This is the same behaviour that can be obtained with the standard gummel-poon model of the transistor.

The difference is that, in your example, the symbol points to your custom schematics:



which is this:



while the ZXT413 doesn't have a specified path for a custom schematic, but there is a spice model dropdown list:



Do you have a custom schematics also for ZTX413, ZTX415 or FMMT417 like taht of the 2N2369? thanks in advance

 

These transistors do not work in relaxers. They need an external trigger.
You can make the model yourself. My model includes the parameters of the transistor, as well as the breakdown voltage of the collector junction and the breakdown voltage of the collector-emitter with a broken base. You can also set the breakdown of the emitter junction. My model tries to simulate the physics of the model, and the model from Zetex is supplemented with various switches. Their goal they have achieved - avalanche operation with external switching.

 

Ok, thank you so much for your help!

 

Cool!

 

Sorry @Bordodynov , could you also give me some references for the spark gap model you implemented in your library? what is the numerical/circuital model that you used as a reference? Thanks in advance!

 

I took the model of the arrester from the person with the nickname Analogspiceman as the basis. This information was on ltwiki. Unfortunately I do not know his real name. I added inertia to his model. I did not make any publications and I had no other sources of information.