UJT model works in SPICE but not Multisim

[dingebre]

I want to use a UJT in a simulation. I've found several SPICE models and have used the one I attached in other SPICE software and it works fine. I can't get this one to work with the "standard" UJT oscillator. Can some kind soul please explain to me where I made a mistake. I'm sure it's simple, but I can't see it.

David 

[OStep]

Hi David,

I believe you have an incorrect symbol-model mapping. The .subckt ports 1,2,3 have logical meanings E, B1, B2, respectively (according to the text file). You must edit your model in the database in order to correct this. I am attaching the fixed model anyway.

Thanks,

[dingebre]

Thank you. I was sure it was something simple.

David

[dingebre]

I'm sorry to be slow, but I don't see what you changed. Could you give me a little more detail, please?

[OStep · Accepted solution]

1. Open Component Properties

2. In the Value tab, press "Edit Component in DB" (you may need to save if it is not in your User/Coporate database)

2. Note the mapping in the model tab (the "Model Nodes" column lists the .subckt ports in the order than they appear in the .subckt statment. According to the comment in Motorola's text file, E should be mapped to the first model port, B1 to the second, and B3 to the third.

I should also mention that you ave an unused .subckt (X2N2646) in your model data. Motorola seems to be providing two independent .subckts representing two variations of the component.

Thanks

[dingebre]

OK, I see what you mean. Thanks Max. It all works now.

David

[usama1000]

facing the same problem! would you please explain this thing in detail, I am unable to understand your statement number 3. "note the maping in the model tab......."  

[OStep]

Let's use this model:

* Motorola IP=.5U IV=6M VB1(sat)=3 Rbb=6.1K Vob1=3.6: E, B1, B2
.SUBCKT X2N2646 1 2 3
DE 1 4 EMITTER
VE 4 5 DC 0
HVE 6 0 VE 1K
RVE 0 6 1MEG
BBB 5 7 I=0.00028*V(5,7)+0.00575*V(5,7)*V(6)
CBB 5 7 35P
RB1 7 2 38.15 RMOD
RB2 3 5 2.518K RMOD
.MODEL RMOD R TC1=.01
.MODEL EMITTER D (IS=21.3P N=1.8)
.Ends

The original model in this post has two redundant .subckts, so it a source of confusion.

I suggest that you use the Component Wizard (under the Tools menu) to create a new UJT component using the above model (simply paste the above text into the model text box). 

See the attached screen capture of the mapping. 

Note that you need to map the symbol pins to the pins on the .subckt line. There is a comment above the .subckt line that (not so cleary) hints that pin 1 is E, pin 2 is B1 and pin 3 is B2. So that is how you need to match them up to the symbol pins.

Let me know if that helps you.

[usama1000]

Thanks Alot, It works fine!

[ultraxp]

Hello,

I have to use in my circuit D5K2, 2N6114 Complementary unijunction transistor. But I don't have any model. Do you have model of these CUJTs or equivalent's? Can UJT transistor model transform to the CUJT model?

Best regards.