# LTSpice - Voltage Controlled Switch in hardware circuit?

I have a question considering LTSpice's voltage Controlled switch ! (http://www.linear.com/solutions/5735)

In my circuit I want to pass on the voltage from one circuit to another with the voltage controlled switch. The switch gets a control signal, which, if >= 1V (or 0.5V), turns the switch on and connects the 2 circuits.

This is currently modelled with a .spice directive. But as I cant do that in hardware, I need to figure something out!

I tried a NPN Transistor, but it didnt really work out as I had to apply the load of the latter circuit to the emitter, what in turn altered the output I was hoping to get !

In short terms: I need something switch that goes "on" when the control voltage is > 0.5 Volt and that doesnt alter the input voltage it is supposed to carry across !

Any ideas are greatly appreciated !

• Wouldn't it be nice to have a VCCS in real life? Apr 6, 2017 at 6:08

Use a comparator (I recommend some small amount of hysteresis) set up to trigger at 0.5V and then use it to drive a low Rds(on) MOSFET. I cannot tell which channel mosfet would be the most useful for your application since you do not mention whether you are doing high or low side switching

• Thanks for your answer ! I have a AND gate that gives me "1" when the switch is supposed to switch to "on" ! So i guess it's a N mosfet ? But how do I model the treshold voltage in LTSpice ? Do you happen to know that? Cheers ! Apr 5, 2017 at 14:37
• I'm assuming you are familiar with comparator circuits so i will omit that part, otherwise I recommend you google them, they are quite a common type of circuit and plenty of information. To simulate the voltage that triggers the comparator you can use the voltage source in the piecewise linear mode Apr 5, 2017 at 17:09
• I'm familiar with comparators, fair enough! By any chance, do you have a rough estimate what the propagation time of such a comparator circuit would come up to (the rough order) ? Apr 5, 2017 at 17:36
• A quick Digikey search says it can vary from 1.3ms down to 0.085ns Apr 5, 2017 at 17:56