Simulating a variable resistance input with LTSpice?
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From: Joerg on 13 Apr 2010 13:58 Hello Folks, Got stuck when trying to simulate an NTC. This temperature-variant resistor will be the only variable input so ".STEP" and stuff do not cut it because that only overlays multiple curve in an AC or DC simulation. I want just one curve: Output of my circuit versus varying NTC resistor value. Tried to make a voltage dependent resistor this way: http://www.electro-tech-online.com/attachments/general-electronics-chat/40714d1269571000-sine-variable-resistor-ltspice-d2.png It works but is incredibly slow. Any better ideas? -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: John Larkin on 13 Apr 2010 14:26 On Tue, 13 Apr 2010 10:58:03 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Hello Folks, > >Got stuck when trying to simulate an NTC. This temperature-variant >resistor will be the only variable input so ".STEP" and stuff do not cut >it because that only overlays multiple curve in an AC or DC simulation. >I want just one curve: Output of my circuit versus varying NTC resistor >value. > >Tried to make a voltage dependent resistor this way: > >http://www.electro-tech-online.com/attachments/general-electronics-chat/40714d1269571000-sine-variable-resistor-ltspice-d2.png > >It works but is incredibly slow. Any better ideas? Do you need a voltage to resistance converter? That's easy if you have a multiplier. Interestingly, LT Spice doesn't provide a multiplier component. John
From: Joerg on 13 Apr 2010 14:53 John Larkin wrote: > On Tue, 13 Apr 2010 10:58:03 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> Hello Folks, >> >> Got stuck when trying to simulate an NTC. This temperature-variant >> resistor will be the only variable input so ".STEP" and stuff do not cut >> it because that only overlays multiple curve in an AC or DC simulation. >> I want just one curve: Output of my circuit versus varying NTC resistor >> value. >> >> Tried to make a voltage dependent resistor this way: >> >> http://www.electro-tech-online.com/attachments/general-electronics-chat/40714d1269571000-sine-variable-resistor-ltspice-d2.png >> >> It works but is incredibly slow. Any better ideas? > > Do you need a voltage to resistance converter? That's easy if you have > a multiplier. Interestingly, LT Spice doesn't provide a multiplier > component. > Well, the one in the link works now. Turns out one shall not get too close to very low values where LTSpice has a hard time. At least it heats my office :-) When do we get some global warming out here? This function stuff is pretty cool. For example, it can be used to get pressure sensor readings from a file into something that electrically resembles the sensor. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jim Thompson on 13 Apr 2010 15:11 On Tue, 13 Apr 2010 10:58:03 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Hello Folks, > >Got stuck when trying to simulate an NTC. This temperature-variant >resistor will be the only variable input so ".STEP" and stuff do not cut >it because that only overlays multiple curve in an AC or DC simulation. >I want just one curve: Output of my circuit versus varying NTC resistor >value. > >Tried to make a voltage dependent resistor this way: > >http://www.electro-tech-online.com/attachments/general-electronics-chat/40714d1269571000-sine-variable-resistor-ltspice-d2.png > >It works but is incredibly slow. Any better ideas? Get this file... VVR.zip VOLTAGE VARIABLE RESISTOR SYMBOL/SUBCIRCUIT On the Subcircuits and Symbols Page of my website. It's just a text file... all you care about is the "Template" line. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy
From: Fred Bartoli on 13 Apr 2010 15:29
Joerg a �crit : > Hello Folks, > > Got stuck when trying to simulate an NTC. This temperature-variant > resistor will be the only variable input so ".STEP" and stuff do not cut > it because that only overlays multiple curve in an AC or DC simulation. > I want just one curve: Output of my circuit versus varying NTC resistor > value. > > Tried to make a voltage dependent resistor this way: > > http://www.electro-tech-online.com/attachments/general-electronics-chat/40714d1269571000-sine-variable-resistor-ltspice-d2.png > > > It works but is incredibly slow. Any better ideas? > The way I'd do it is with a B current source (OK, sink). Basically you measure voltage across the NL resistor nodes (a,b) and sink a current between these nodes which is your NL function of V(a,b). That also better handles the R=0 pathological case, because you're less tempted to allow infinite current flow :-) -- Thanks, Fred. |