dc-dc step down converter model and the command of a JFET in LTspice

I am trying to reproduce this command circuit of a JFET semiconductor: and there are many components I am struggling to reproduce in LTspice. For instance, for the dc-dc converter, does LTspice provide a simple model or do I have to remake it from scratch? Also, this figure is a screen shot of the datasheet of the component of interest. Is an IXDD component an "AND component"? and What about the Opto part? This has been bothering me for quite a while now. I woud be very appreciative for pieces of advice and your help.

• Modelling of the DC-DC converter is optional, for a low fidelity model, it can be replaced by a 6V voltage source.
– AJN
May 20 at 9:06
• @AJN Understood, thank you. May 25 at 6:34

• @SteKulov That's true, but the simple diode could be modelled with a relatively large cjo, and the current lowpass filtered and with a schmitt, for example. The effect is a diminishing trigger the higher the frequency. I'm not saying it's perfect, or that's how it should be done, just that it could be, in the same way the "simple voltage/current" approach wouldn't (that's why I added "unless there are specifics"). The PWM will suffer, yes, but if all the effects are needed, then you're into more than just a behavioural model. May 20 at 21:08