Simulating a variable resistance input with LTSpice?
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From: Jim Thompson on 13 Apr 2010 20:16 On Tue, 13 Apr 2010 17:03:55 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Tue, 13 Apr 2010 23:08:23 +0200, "Helmut Sennewald" ><helmutsennewald(a)t-online.de> wrote: > >>"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> schrieb im >>Newsbeitrag news:sfd9s511ormdiedjk9o725omcntmkttgpq(a)4ax.com... >>> 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 >> >> >>Hello John, >> >>LTspice has B-deviecs. They can do a lot of math. >>* >>** power >>/ divide >>sin >>tanh >>exp >> >>See the help pages for B-devices. >>The B-device is the best device to implement a NTC-resistor >>with it's exponential resistance versus temperature function. >> >>The LTspice Yahoo group provides examples. >> >>Best regards, >>Helmut >> >> >> > >Sure, but a canned multiplier component would be handy, without a >bunch of typing. As would an ideal diode. At least they have ideal >opamps. > >John Lazy spat wearer, can't even roll his own B-devices ;-) ...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: Joerg on 13 Apr 2010 20:28 Jim Thompson wrote: > On Tue, 13 Apr 2010 15:10:51 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> Jim Thompson 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? >>> Sorry, Joerg, I misread your need. It's actually quite simple, IF you >>> can describe the TC with coefficients of T and T^2... make your own >>> resistor model: >>> >>> Resistor >>> >>> General form >>> >>> R<name> <(+) node> <(-) node> [model name] <value> >>> + [TC = <TC1> [,<TC2>]] >>> >>> TC1, and TC2 are the linear and squared coefficients, respectively. >>> >>> See the LTspice manual for clarity (the above was pasted from >>> PSPCREF.pdf) >>> >> In the current case it's a whole lot uglier than that, see under >> "Inverse of the equation": >> >> http://en.wikipedia.org/wiki/Steinhart%E2%80%93Hart_equation >> >> T (Temperature) must be scooted. I think LTSpice will have a cow when I >> try this. > > Then use a resistance vs temperature table... trivial in PSpice, > probably so in LTspice. > > Besides, that smells like unnecessary obfuscation :-) > Depends on the client, how much precision they want, how much MIPS is there, how much RAM is there. > What kind of NTC? > Just the regular kind, silicon-based resistor. > They're usually spec's as R = Ro*e^(beta*(1/T-1/To)) > In industry it's usually the 2-term or the 3-term Steinhart-Hart equation. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 13 Apr 2010 20:31 John Larkin wrote: > On Tue, 13 Apr 2010 23:08:23 +0200, "Helmut Sennewald" > <helmutsennewald(a)t-online.de> wrote: > >> "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> schrieb im >> Newsbeitrag news:sfd9s511ormdiedjk9o725omcntmkttgpq(a)4ax.com... >>> 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 >> >> Hello John, >> >> LTspice has B-deviecs. They can do a lot of math. >> * >> ** power >> / divide >> sin >> tanh >> exp >> >> See the help pages for B-devices. >> The B-device is the best device to implement a NTC-resistor >> with it's exponential resistance versus temperature function. >> >> The LTspice Yahoo group provides examples. >> >> Best regards, >> Helmut >> >> >> > > Sure, but a canned multiplier component would be handy, without a > bunch of typing. As would an ideal diode. At least they have ideal > opamps. > There are modulators though, regular and I/Q, under special functions. -- 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 20:33 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? Thompson's Fundamental Rule #1, Stay away from PhD's, use this instead.... http://www.efunda.com/designstandards/sensors/thermistors/thermistors_theory.cfm Do you really have one bad enough to need the high order corrections? ...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: Jim Thompson on 13 Apr 2010 20:46
On Tue, 13 Apr 2010 17:28:51 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Jim Thompson wrote: >> On Tue, 13 Apr 2010 15:10:51 -0700, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> Jim Thompson 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? >>>> Sorry, Joerg, I misread your need. It's actually quite simple, IF you >>>> can describe the TC with coefficients of T and T^2... make your own >>>> resistor model: >>>> >>>> Resistor >>>> >>>> General form >>>> >>>> R<name> <(+) node> <(-) node> [model name] <value> >>>> + [TC = <TC1> [,<TC2>]] >>>> >>>> TC1, and TC2 are the linear and squared coefficients, respectively. >>>> >>>> See the LTspice manual for clarity (the above was pasted from >>>> PSPCREF.pdf) >>>> >>> In the current case it's a whole lot uglier than that, see under >>> "Inverse of the equation": >>> >>> http://en.wikipedia.org/wiki/Steinhart%E2%80%93Hart_equation >>> >>> T (Temperature) must be scooted. I think LTSpice will have a cow when I >>> try this. >> >> Then use a resistance vs temperature table... trivial in PSpice, >> probably so in LTspice. >> >> Besides, that smells like unnecessary obfuscation :-) >> > >Depends on the client, how much precision they want, how much MIPS is >there, how much RAM is there. > > >> What kind of NTC? >> > >Just the regular kind, silicon-based resistor. > > >> They're usually spec's as R = Ro*e^(beta*(1/T-1/To)) >> > >In industry it's usually the 2-term or the 3-term Steinhart-Hart equation. It's "usually" the equation I cited... I have several books here that say so ;-) And it's trivial to do in Spice. ...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 |