Voltage-Controlled Capacitor Spice Model now on my website.
See VControlledCap.zip on the Device Models & Subcircuits Page.
Includes Library File (.LIB), LTspice Symbol (.ASY), and a JPEG
showing how it was developed.
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Voltage-variable capacitor doesn't work in LTSpice
Started by ●March 16, 2015
Reply by ●March 18, 20152015-03-18
Reply by ●March 18, 20152015-03-18
On Wed, 18 Mar 2015 09:28:57 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:>Voltage-Controlled Capacitor Spice Model now on my website. > >See VControlledCap.zip on the Device Models & Subcircuits Page. > >Includes Library File (.LIB), LTspice Symbol (.ASY), and a JPEG >showing how it was developed. > > ...Jim ThompsonI don't have time to play with this just now, but one quick question: Given that C is a variable capacitor, set C to 1F and charge it to 1 volt. Now change C to 0.5F. What is the new voltage? -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●March 18, 20152015-03-18
On Wed, 18 Mar 2015 10:30:44 -0700, John Larkin wrote:> On Wed, 18 Mar 2015 09:28:57 -0700, Jim Thompson > <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: > >>Voltage-Controlled Capacitor Spice Model now on my website. >> >>See VControlledCap.zip on the Device Models & Subcircuits Page. >> >>Includes Library File (.LIB), LTspice Symbol (.ASY), and a JPEG showing >>how it was developed. >> >> ...Jim Thompson > > I don't have time to play with this just now, but one quick question: > > Given that C is a variable capacitor, set C to 1F and charge it to 1 > volt. Now change C to 0.5F. What is the new voltage?How many 1 farad capacitors are you aware of? Oh and would not a 1F charged cap dump into a 0.5F cap and fully charge it? If that answer is yes, then the voltage would be the same... slightly less even, all elements considered. You thought it would morph the EMF into something else?
Reply by ●March 18, 20152015-03-18
On Wed, 18 Mar 2015 17:40:06 +0000 (UTC), DecadentLinuxUserNumeroUno <DLU1@DecadentLinuxUser.org> wrote:>On Wed, 18 Mar 2015 10:30:44 -0700, John Larkin wrote: > >> On Wed, 18 Mar 2015 09:28:57 -0700, Jim Thompson >> <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >> >>>Voltage-Controlled Capacitor Spice Model now on my website. >>> >>>See VControlledCap.zip on the Device Models & Subcircuits Page. >>> >>>Includes Library File (.LIB), LTspice Symbol (.ASY), and a JPEG showing >>>how it was developed. >>> >>> ...Jim Thompson >> >> I don't have time to play with this just now, but one quick question: >> >> Given that C is a variable capacitor, set C to 1F and charge it to 1 >> volt. Now change C to 0.5F. What is the new voltage? > > How many 1 farad capacitors are you aware of?In LT Spice, you can use any C value. 1F is the generic capacitor. I usually normalize theoretical circuits to 1F, 1H, 1 ohm. [1] In real life, Digikey will sell you 1F caps. Or 5000F caps. But not variable 1F caps.> > Oh and would not a 1F charged cap dump into a 0.5F cap and fully charge >it? If that answer is yes, then the voltage would be the same... >slightly less even, all elements considered. > > You thought it would morph the EMF into something else?I'd like to know if Jim's model conserves charge, or conserves energy, or conserves voltage. Or whatever it does. [1] I do find myself picking standard values, like 39nF instead of 40 nF, and worrying about leakage and stray capacitance and power dissipation, when none of these matter in Spice. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●March 18, 20152015-03-18
On Wed, 18 Mar 2015 10:30:44 -0700, John Larkin <jlarkin@highlandtechnology.com> wrote:>On Wed, 18 Mar 2015 09:28:57 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: > >>Voltage-Controlled Capacitor Spice Model now on my website. >> >>See VControlledCap.zip on the Device Models & Subcircuits Page. >> >>Includes Library File (.LIB), LTspice Symbol (.ASY), and a JPEG >>showing how it was developed. >> >> ...Jim Thompson > >I don't have time to play with this just now, but one quick question: > >Given that C is a variable capacitor, set C to 1F and charge it to 1 >volt. Now change C to 0.5F. What is the new voltage?I haven't tried that. Since it _is_ a capacitor, it'll depend on whether a simulator treats capacitors as charge-controlled devices or otherwise. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●March 18, 20152015-03-18
Voltage-Controlled Resistor Spice Model Updated
See VVR.zip on the Device Models & Subcircuits Page of my website
Includes Library File (.LIB), LTspice Symbol (.ASY), PSpice Symbol
(.SYM)and a JPEG showing how it was developed.
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Reply by ●March 18, 20152015-03-18
On 17/03/2015 00:26, Joerg wrote:> Gentlemen, > > Setting up voltage-controlled resistors is easy: R=(V(X)+0.01) or > whatever. Works, always did. Doing the same with a capacitor fails with > this error message: > > Error on line 6 : c1 n002 0 c=(v(x)+0.01) > Unable to find definition of model "c" > > * Unknown parameter "x" > WARNING: Less than two connections to node X. This node is used by V4. > Fatal Error: Missing capacitance value for "C1" > > Both sims attached. What gives? Ideas how to make it work? Disregard the > values that wouldn't make sense for the cap here, this is just to find > the principal reason why the control method doesn't work with capacitors. ><snip> This is what I did for a time-varying capacitance. In the component 'Value' field, I put Q=(4p/(0.25 +(time*5)))*x which swept the capacitance from 16pF downwards controlled by the internal variable 'time'. I can't remember why you need the Q and the x, but you do, and it took a good while to find out - it seems you can't just vary the capacitance directly. Replace time with a voltage and the appropriate scaling and you should be good to go. Cheers -- Syd
Reply by ●March 18, 20152015-03-18
On 2015-03-18 11:54 AM, Syd Rumpo wrote:> On 17/03/2015 00:26, Joerg wrote: >> Gentlemen, >> >> Setting up voltage-controlled resistors is easy: R=(V(X)+0.01) or >> whatever. Works, always did. Doing the same with a capacitor fails with >> this error message: >> >> Error on line 6 : c1 n002 0 c=(v(x)+0.01) >> Unable to find definition of model "c" >> >> * Unknown parameter "x" >> WARNING: Less than two connections to node X. This node is used by V4. >> Fatal Error: Missing capacitance value for "C1" >> >> Both sims attached. What gives? Ideas how to make it work? Disregard the >> values that wouldn't make sense for the cap here, this is just to find >> the principal reason why the control method doesn't work with capacitors. >> > <snip> > > This is what I did for a time-varying capacitance. In the component > 'Value' field, I put Q=(4p/(0.25 +(time*5)))*x which swept the > capacitance from 16pF downwards controlled by the internal variable 'time'. > > I can't remember why you need the Q and the x, but you do, and it took a > good while to find out - it seems you can't just vary the capacitance > directly. Replace time with a voltage and the appropriate scaling and > you should be good to go. >Tried it and that completely bungled the linearity when the cap is inside a resonant circuit. At least no more error messages which is good. Well, maybe I just do it in hardware then, firing up the old Weller. I'd have to buy a bag of varicaps but those are cheap. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●March 18, 20152015-03-18
On Wed, 18 Mar 2015 13:36:27 -0700, Joerg <news@analogconsultants.com> wrote:>On 2015-03-18 11:54 AM, Syd Rumpo wrote: >> On 17/03/2015 00:26, Joerg wrote: >>> Gentlemen, >>> >>> Setting up voltage-controlled resistors is easy: R=(V(X)+0.01) or >>> whatever. Works, always did. Doing the same with a capacitor fails with >>> this error message: >>> >>> Error on line 6 : c1 n002 0 c=(v(x)+0.01) >>> Unable to find definition of model "c" >>> >>> * Unknown parameter "x" >>> WARNING: Less than two connections to node X. This node is used by V4. >>> Fatal Error: Missing capacitance value for "C1" >>> >>> Both sims attached. What gives? Ideas how to make it work? Disregard the >>> values that wouldn't make sense for the cap here, this is just to find >>> the principal reason why the control method doesn't work with capacitors. >>> >> <snip> >> >> This is what I did for a time-varying capacitance. In the component >> 'Value' field, I put Q=(4p/(0.25 +(time*5)))*x which swept the >> capacitance from 16pF downwards controlled by the internal variable 'time'. >> >> I can't remember why you need the Q and the x, but you do, and it took a >> good while to find out - it seems you can't just vary the capacitance >> directly. Replace time with a voltage and the appropriate scaling and >> you should be good to go. >> > >Tried it and that completely bungled the linearity when the cap is >inside a resonant circuit. At least no more error messages which is >good. Well, maybe I just do it in hardware then, firing up the old >Weller. I'd have to buy a bag of varicaps but those are cheap.Are you trying to sim a VCO? Simulating oscillators is always tedious. You could use a diode model, which does include variable capacitance. https://dl.dropboxusercontent.com/u/53724080/Circuits/Caps/Cap_Sweep.asc Try to get the Skyworks sample kit. It has a lot of varicaps, and many other cool things. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●March 18, 20152015-03-18
On Wed, 18 Mar 2015 18:54:11 +0000, Syd Rumpo <usenet@nononono.co.uk> wrote:>On 17/03/2015 00:26, Joerg wrote: >> Gentlemen, >> >> Setting up voltage-controlled resistors is easy: R=(V(X)+0.01) or >> whatever. Works, always did. Doing the same with a capacitor fails with >> this error message: >> >> Error on line 6 : c1 n002 0 c=(v(x)+0.01) >> Unable to find definition of model "c" >> >> * Unknown parameter "x" >> WARNING: Less than two connections to node X. This node is used by V4. >> Fatal Error: Missing capacitance value for "C1" >> >> Both sims attached. What gives? Ideas how to make it work? Disregard the >> values that wouldn't make sense for the cap here, this is just to find >> the principal reason why the control method doesn't work with capacitors. >> ><snip> > >This is what I did for a time-varying capacitance. In the component >'Value' field, I put Q=(4p/(0.25 +(time*5)))*x which swept the >capacitance from 16pF downwards controlled by the internal variable 'time'. > >I can't remember why you need the Q and the x, but you do, and it took a >good while to find out - it seems you can't just vary the capacitance >directly. Replace time with a voltage and the appropriate scaling and >you should be good to go. > >CheersQ is charge and X is the cap voltage. Q = (expression) * X just means that (expression) is the capacitance. Seems silly to me. http://ltwiki.org/LTspiceHelp/LTspiceHelp/C_Capacitor.htm I tried a capacitor that changes value abruptly at 0 volts, like the example. That works. If I try to change C abruptly at a non-zero voltage, the sim crashes. Some conservation thingie was violated. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
