Time domain simulation - voltage controlled switch

Hi everyone,

After a lot of "debugging" I still can't get the most basic voltage controlled switch to work:


Any help would be greatly appreciated.

Many thanks dbro

by dbro
April 15, 2015


Both simulations work correctly.

Perhaps you misunderstand how they should behave.

What would you expect the voltage across a 1R resistor to do if you connect and disconnect it to a -1V power supply with a switch that has a very large OFF resistance (approx 1e15 Ohms) and a 0.1R ON resistance?

The MOSFET example is a little harder to interpret because you have connected the source of the fet to a -1V supply so you have at most a -4V Vgs with which to turn the MOSFET on.

The sinewave gate drive has slow edges and the MOSFET has a relatively low gain (actually transconductance: Iout/Vin) so the voltage across the resistor turns on and off slowly and, due to the modest maximum Vgs, the MOSFET never turns fully on so some voltage is dropped across it. Therefore the voltage across the resistor is somewhat less that the -1V you might expect.


by signality
April 15, 2015

signality, thanks for getting back so quickly!

Actually I'm happy with the behavior up to a simulation time of 16s; it's when I try 17s or longer that the simulation fails.

Sorry, I should have made this clearer :( my bad). I have edited the circuit so the simulation time is 17s. Solver now reports the error:

Solver Aborted - Error in Transient Solver nonfinite scale

:( dbro

by dbro
April 15, 2015


thanks for all your help and suggestions, which I will follow up.

:) dbro

by dbro
April 16, 2015

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