PWM & transformer spice modeling using functional block

I had just downloaded the jumbocad. I want to simulate my flyback converter. However its magnetic core model didn't work.
The jumbocad schematic provide a lot of functional block such as gain, differentiator, integrator, multiplier, limiter, voltage & current source.....etc.
I want to create my transformer and PWM model using the functional block, can someone provide some examples showing how to construct a PWM and transformer model using functional block ?