Setting the Saturation V_ce and V_be in LTSpice

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Rainier Azucena

Joined Dec 18, 2015
7
I've been doing a few test with BJTs. A lot of times it's just easier to see how the general ideas pan out, so turning of a few nuisances and idealizing everything is great. But I can't seem to find a direct way to set both Saturation V_ce and V_be of NPN to 0V. How do I do it? It's not explicitly defined so does it only arise from the other parameters?
 

crutschow

Joined Mar 14, 2008
23,783
I've been doing a few test with BJTs. A lot of times it's just easier to see how the general ideas pan out, so turning of a few nuisances and idealizing everything is great. But I can't seem to find a direct way to set both Saturation V_ce and V_be of NPN to 0V. How do I do it? It's not explicitly defined so does it only arise from the other parameters?
It is defined by other BJT parameters, but I don't think you can readily adjust them to make Vce and Vbe equal to zero.
If you really want to simulate an ideal BJT (and I see no good reason to do that) then you can use the current-dependent current-source (f) located in the component selection window.
Read the Help file on it to determine how to set the parameters for the desired operation.
 

WBahn

Joined Mar 31, 2012
24,974
I think most device models are moving to parameterized models instead of physics-based models -- this means that the device behavior is defined via polynomial curve fitting to actual data. This is certainly true for process models, but I imagine that a lot of existing discrete models are still physics-based just because there's no compelling reason to change. But even with the physics-based models the Vce and Vbe voltages are derived. They are NOT constants -- that would almost completely defeat the whole point of the simulator!
 
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