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I am trying to reproduce this command circuit of a JFET semiconductor: enter image description here 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.

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    \$\begingroup\$ Modelling of the DC-DC converter is optional, for a low fidelity model, it can be replaced by a 6V voltage source. \$\endgroup\$
    – AJN
    May 20 at 9:06
  • \$\begingroup\$ @AJN Understood, thank you. \$\endgroup\$
    – Wallflower
    May 25 at 6:34
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Making a model is not easy work. Your interest should be the behaviour of the model, not the exact, nitty-gritty details of its internals. That's not to say that you can't go that way, there are people who made transistor-level 741s, and more, but those models will also be very slow in terms of simulation time.

Therefore, as AJN mentions, the converter can be replaced by a voltage source, referenced to the local ground. IXDD509 seems to be an IXYS component. And the opto-coupler, is an opto-coupler. Unless there are specifics about it, a diode and a current sensor should do (or even some voltge/current source, for even more simplicity).

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    \$\begingroup\$ PWM gets wrecked by optos when you go up in frequency. When that happens, not all the duty cycles can make it through. So the specific part# and end-application is going to play into what needs to be modeled on that opto. \$\endgroup\$
    – Ste Kulov
    May 20 at 21:03
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    \$\begingroup\$ @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. \$\endgroup\$ May 20 at 21:08
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    \$\begingroup\$ Roger that. I just wanted to point out to the questioner that there is going to be nuances with this. Based on how the question was asked, it seems like they just wanted to plug n' chug parts in...which might not work out without a better understanding of the problem they're trying to model or solve. Your comment adds sufficient context to that. thumbs-up \$\endgroup\$
    – Ste Kulov
    May 21 at 5:37
  • \$\begingroup\$ @aconcernedcitizen Understood, thank you for your response. We actually are trying to model a converter in LTspice and with that comes the command of the semiconductor that I had troubles performing. \$\endgroup\$
    – Wallflower
    May 25 at 6:25

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