Modeling a switch in LTspice

[carbonzit]

Sometimes it seems the simplest things are the hardest to deal with ...

I'd like to model this circuit in LTspice:

**broken link removed**

In order to test it, I need to be able to "throw" the switches. How do I do that? For instance, I'll run the simulation for one second, and I want to throw the "set" switch half a second after starting.

I'm guessing this falls under the heading of "behavioral" circuit elements, but I have no clue as to how to implement it. Any (hopefully) simple way of doing this?

 

[Mikebits]

I use voltage controlled switch. See asc file for example.

 

[Mikebits]

Here is a switch model I found on the net. Have not used it, but I am sure it will work.

 

[Mikebits]

Oh, I see what your asking. Right click the switch in LTspice, in the component attribute editor in the value box you can set switch to on/off eg. value SW1 On
For real time control, I dunno.

 

[carbonzit]

No, actually your first idea what what I needed, something that can be automagically switched during the simulation. I tried it and it works fine. Thanks.

Pretty clunky to implement on the schematic, though. What I'd really like would be a SPICE subcircuit, called "switch" that just appears on the schematic as a single 2-terminal component and which I can set to close (or open) at some specified time. I hate having to include all those stray .model directives and such on a nice neat schematic. So I'll play around with this. (Any advice how to do this appreciated.)

 

[simonbramble]

I have designed a switch circuit that I have stored in a file called 'switch'. I then just copy and paste it into any circuit I need. Yes it is a pain to implement everytime. Alternatively, you can do the same above with MOSFETs - one of the internal models in LTSpice. The ON resistance is so low, it can be assumed to be as good as a switch. Control it with a Pulse voltage source. I use a MOSFET when I can get away with it purely for simplicity

 

[crutschow]

Electronic Workbench from Multisim has a simple switch that can be controlled from a keyboard key while the simulation is running, which is very handy. Unfortunately LTspice does not seem to support such a feature.

 

[carbonzit]

I have designed a switch circuit that I have stored in a file called 'switch'. I then just copy and paste it into any circuit I need. Yes it is a pain to implement everytime.

Yes, it is. But I believe LTspice gives you all the "hooks" one needs in order to implement this in a neat package that could actually be chosen from the "component" menu, by building a .subckt and attaching it to an .asy symbol. Anyone know enough about this program to tell us how to do that?

 

[simonbramble]

Hmmm. I've had a think about this... How would making it into a subckt make it any simpler? You still need a switch input and output and I/O to provide a drive signal to activate the switch. The only thing you can simplify is the ON resistance. Regardless you would still need a .subckt command to specify it, so you might as well import your own library part... Attached is the file I use if it helps (just remove V1)

 

[ericgibbs]

Hmmm. I've had a think about this... How would making it into a subckt make it any simpler? You still need a switch input and output and I/O to provide a drive signal to activate the switch. The only thing you can simplify is the ON resistance. Regardless you would still need a .subckt command to specify it, so you might as well import your own library part... Attached is the file I use if it helps (just remove V1)

hi simon
I also use a 'master' asc on which I have common components with their includes. Arranged such that they can be copied and pasted in a couple of seconds, to a new asc file.

I would say that its important that the components used should be kept as standard as possible if its intended that the asc files be shared with other LTS users.

 

[Mikebits]

Eric, that sounds really handy.

 

[simonbramble]

You can always open up 2 schematics - one with the library part (switch.asc) and one with the schematic you are editing, then use <F6> to copy from one to the other. it is clunky, but I use this every time