UC3842 model is not working at all

Question

Greetings, I am trying to simulate switching regulator circuits with Multisim 10.
Specifically, I am trying to use the UC3844 model to create a boost regulator, buck regulator, and eventually a flyback regulator.
The UC3844 part is pretty easy to work with in real life, but is not functional in Multisim10.
The datasheet is from texas instruments -- SLUS223C
Try the example circuit on Page 7 from SLUS223C in Multisim.
I noticed that the Vref pin never has 5Vdc present during the simulation.  In real life, there is always 5Vdc present on the Vref pin as soon as the DC voltage on VCC rises above 16Vdc.
It's as though the part is not turning on or is stuck in undervoltage lockout.
Can anyone explain how this part is supposed to work in multisim 10, or is there a working example multisim simulation example I can reference?

Answer 1

kiki_barrios,
Hello - attached is the UC3842 model you are looking for in v10.1 in a flyback topology (modified from existing SMPS samples).   I suggest that for Switch Mode Power Controllers that you also reference the SMPS samples (File -> Open Samples -> SMPS).   Many of sample circuits in the topologies shown have corresponding SMPS controller ICs models with parametric values that allow you to match the specifications closely with the manufacturer's IC specifications.  The sample I included swapped out the BASSO model for the UC3842 model.
Recently a customer looking for a Linear Technologies SMPS controller (not in the DB) was successfully able to use a corresponding PWMCM BASSO model in lieu of the actual mfg SPICE model as many of these are propietary or encrypted.  
These BASSO models are relatively easy to use.  For a given topology (CM or VM, buck, boost, flyback), open up the sample circuit.  Adjust the model by opening up the SPICE model of the controller within the circuit (Double-click on part -> Edit Model button).   Adjust the 'Current Instance Parameters:' to match those found on the datasheet as shown below.  
Multisim customers that are using these, say there is close agreement to the simulations compared to what they see on the benchtop during verification testing.
Also in general I find when using these SMPS samples in your own applications, adjusting the simustion engine parameters 'RSHUNT' a few decades down (from default of 10^12 -> 10^11 or 10^10) [due to high C, L values] and adjusting the integration method 'METHOD' from 'trapezoidal' to 'gear' [due to switching signals] allows for better convergence performance of these models and SMPS circuits in general.   These settings are found in the Multisim menu as follows: (Simulate -> Interactive Simulation Settings -> Analysis Options [tab]-> Select 'Use custom settings' (hit 'Customize' button) -> locate/change the corresponding engine paramenters as indicated above).
By the way,  Basso's 'Switch-Mode Power Supply SPICE Cookbook ' is also a good reference for your design requirements as the examples in this Multisim sample folder are based on this book.
Hope this helps.
Regards,
Patrick Noonan
National Instruments
Attachments:
Flyback_VM_UC3842.ms10 ‏146 KB