The following is a Q and A and Q I posted on a Yahoo group. I didn't get the info I needed to procede. Please read the exchange and see if you could help with my lack of info. .............................................................................................. Q. I have noted the switch (SW) that comes with Ltspice has ½ ohm of resistance between contacts. I would like to modify it to be an ideal switch. When I do a control/right click, the sw has no value or spiceline attributes. zero ohms, zero capacitance, etc. may not compute, so I could set them very low. I have the printed users manual in front of me and still can't figure it out.
Please describe how to display and change the qualities of the SW or any other device. Step by step advice would best help me. Thanks, Mike .................................................................................................. A. The switch (SW) requires a .model line. In this line you can set the Ron and Roff values (and other parameters).. This is an example taken from the help file: .model MySwitch SW(Ron=.1 Roff=1Meg Vt=0 Vh=-.5 Lser=10n Vser=.6)
The following are the default values of the parameters
Voltage Controlled Switch Model Parameters
name parameter units default
--------------------------------------------- Vt threshold voltage Volts 0. Vh hysteresis voltage Volts 0. Ron on resistance Ohms 1. Roff off resistance Ohms 1/gmin Lser series inductance Henry 0. Vser series voltage Volts 0. ilimit current limit Amps infin.
To get an almost ideal switch put Ron=1u and Roff=1000G ............................................................................................ Q. I am sorry, but I don't know where to put this info. I've tried opening the component atribute editor, changing the prefix to X and adding the info to the spiceline, among other things without success. Where do I install a .model? And then how do I pull it up to make a schematic?
Thanks again, Mike