On 23 Okt., 00:30, Joerg <inva...@invalid.invalid> wrote:> langw...@fonz.dk wrote: > > On 22 Okt., 23:23, Joerg <inva...@invalid.invalid> wrote: > >> Folks, > > >> Looked at Digikey and some others. Where are those huge capacitance > >> varicaps? The ones with several hundred pF of range for AM radios. All > >> gone lalaland by now? > > >> Even the ones I found in the 100pF range are either obsolete or not > >> recommended for new designs. > > >> What I am trying to do: I need to control a switcher chip in frequency > >> because I've got a very resonant load to deal with. Unfortunately it > >> sets the frequency with a timing cap. I'll have to somehow vary that > >> between 750pF and 2000pF. Can also be digital but then with a > >> granularity of 5pF. The sawtooth voltage across it is 2.5Vpp. > > >> Doing it with caps and a mux chip or two has its own challenges. The > >> ADG-series from AD is around 11pF per pin, otherwise their Rdson is too > >> high. Talking about the a rock and a hard spot here. > > >> Oh, and cost is not very important. If a diode or two or three are > >> needed that cost $5 a pop that's ok. > > >> -- > >> Regards, Joerg > > >>http://www.analogconsultants.com/ > > > possible to force you own triangle in? > > Not on this one. It issues a major reset pulse of almost 50mA and if > that sees any obstructions it all goes bonkers. It already does when you > tough it with a 10k resistor, like the princess on the pea. > > -- > Regards, Joerg > > http://www.analogconsultants.com/this too crazy? http://www.falstad.com/circuit/e-capmult.html -Lasse
Large capacitance varicaps, where are thee?
Started by ●October 22, 2012
Reply by ●October 22, 20122012-10-22
Reply by ●October 22, 20122012-10-22
langwadt@fonz.dk wrote:> On 23 Okt., 00:30, Joerg <inva...@invalid.invalid> wrote: >> langw...@fonz.dk wrote: >>> On 22 Okt., 23:23, Joerg <inva...@invalid.invalid> wrote: >>>> Folks, >>>> Looked at Digikey and some others. Where are those huge capacitance >>>> varicaps? The ones with several hundred pF of range for AM radios. All >>>> gone lalaland by now? >>>> Even the ones I found in the 100pF range are either obsolete or not >>>> recommended for new designs. >>>> What I am trying to do: I need to control a switcher chip in frequency >>>> because I've got a very resonant load to deal with. Unfortunately it >>>> sets the frequency with a timing cap. I'll have to somehow vary that >>>> between 750pF and 2000pF. Can also be digital but then with a >>>> granularity of 5pF. The sawtooth voltage across it is 2.5Vpp. >>>> Doing it with caps and a mux chip or two has its own challenges. The >>>> ADG-series from AD is around 11pF per pin, otherwise their Rdson is too >>>> high. Talking about the a rock and a hard spot here. >>>> Oh, and cost is not very important. If a diode or two or three are >>>> needed that cost $5 a pop that's ok. >>>> -- >>>> Regards, Joerg >>>> http://www.analogconsultants.com/ >>> possible to force you own triangle in? >> Not on this one. It issues a major reset pulse of almost 50mA and if >> that sees any obstructions it all goes bonkers. It already does when you >> tough it with a 10k resistor, like the princess on the pea. >> >> -- >> Regards, Joerg >> >> http://www.analogconsultants.com/ > > this too crazy? http://www.falstad.com/circuit/e-capmult.html >Not crazy at all but there can't be an R3 in my case. Falls apart when it gets into the tens of ohms. It's sawtooth, not triangular. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●October 22, 20122012-10-22
Les Cargill wrote:> Joerg wrote: >> Folks, >> >> Looked at Digikey and some others. Where are those huge capacitance >> varicaps? The ones with several hundred pF of range for AM radios. All >> gone lalaland by now? >> >> Even the ones I found in the 100pF range are either obsolete or not >> recommended for new designs. >> >> What I am trying to do: I need to control a switcher chip in frequency >> because I've got a very resonant load to deal with. Unfortunately it >> sets the frequency with a timing cap. I'll have to somehow vary that >> between 750pF and 2000pF. Can also be digital but then with a >> granularity of 5pF. The sawtooth voltage across it is 2.5Vpp. >> >> Doing it with caps and a mux chip or two has its own challenges. The >> ADG-series from AD is around 11pF per pin, otherwise their Rdson is too >> high. Talking about the a rock and a hard spot here. >> >> Oh, and cost is not very important. If a diode or two or three are >> needed that cost $5 a pop that's ok. >> > > > Could something like this be a start? > > http://www.timeelectronics.com/products/category/decade-boxes/1071-capacitance-box > > > Gets pretty close - 10 pF resolution if I read that right. >Then we'd have to ship a bearded professor in SMT size with every board, for the self-alignment routine :-) -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●October 22, 20122012-10-22
On Mon, 22 Oct 2012 14:22:49 -0700, Joerg <invalid@invalid.invalid> wrote:>Folks, > >Looked at Digikey and some others. Where are those huge capacitance >varicaps? The ones with several hundred pF of range for AM radios. All >gone lalaland by now?http://www.angelfire.com/electronic2/index1/VariableCap.html About half way down.>Even the ones I found in the 100pF range are either obsolete or not >recommended for new designs.No kiddin? ;-)>What I am trying to do: I need to control a switcher chip in frequency >because I've got a very resonant load to deal with. Unfortunately it >sets the frequency with a timing cap. I'll have to somehow vary that >between 750pF and 2000pF. Can also be digital but then with a >granularity of 5pF. The sawtooth voltage across it is 2.5Vpp.Use a regulator with an external clock. That's what we do (all of our switchers are synchronized).>Doing it with caps and a mux chip or two has its own challenges. The >ADG-series from AD is around 11pF per pin, otherwise their Rdson is too >high. Talking about the a rock and a hard spot here. > >Oh, and cost is not very important. If a diode or two or three are >needed that cost $5 a pop that's ok.A regulator with an external clock shouldn't be an issue, then.
Reply by ●October 22, 20122012-10-22
On 23 Okt., 01:08, Joerg <inva...@invalid.invalid> wrote:> langw...@fonz.dk wrote: > > On 23 Okt., 00:30, Joerg <inva...@invalid.invalid> wrote: > >> langw...@fonz.dk wrote: > >>> On 22 Okt., 23:23, Joerg <inva...@invalid.invalid> wrote: > >>>> Folks, > >>>> Looked at Digikey and some others. Where are those huge capacitance > >>>> varicaps? The ones with several hundred pF of range for AM radios. All > >>>> gone lalaland by now? > >>>> Even the ones I found in the 100pF range are either obsolete or not > >>>> recommended for new designs. > >>>> What I am trying to do: I need to control a switcher chip in frequency > >>>> because I've got a very resonant load to deal with. Unfortunately it > >>>> sets the frequency with a timing cap. I'll have to somehow vary that > >>>> between 750pF and 2000pF. Can also be digital but then with a > >>>> granularity of 5pF. The sawtooth voltage across it is 2.5Vpp. > >>>> Doing it with caps and a mux chip or two has its own challenges. The > >>>> ADG-series from AD is around 11pF per pin, otherwise their Rdson is too > >>>> high. Talking about the a rock and a hard spot here. > >>>> Oh, and cost is not very important. If a diode or two or three are > >>>> needed that cost $5 a pop that's ok. > >>>> -- > >>>> Regards, Joerg > >>>>http://www.analogconsultants.com/ > >>> possible to force you own triangle in? > >> Not on this one. It issues a major reset pulse of almost 50mA and if > >> that sees any obstructions it all goes bonkers. It already does when you > >> tough it with a 10k resistor, like the princess on the pea. > > >> -- > >> Regards, Joerg > > >>http://www.analogconsultants.com/ > > > this too crazy?http://www.falstad.com/circuit/e-capmult.html > > Not crazy at all but there can't be an R3 in my case. Falls apart when > it gets into the tens of ohms. It's sawtooth, not triangular. > > -- > Regards, Joerg > > http://www.analogconsultants.com/I'm just guessing, diode across R3 ? -Lasse
Reply by ●October 22, 20122012-10-22
langwadt@fonz.dk wrote:> On 23 Okt., 01:08, Joerg <inva...@invalid.invalid> wrote: >> langw...@fonz.dk wrote: >>> On 23 Okt., 00:30, Joerg <inva...@invalid.invalid> wrote: >>>> langw...@fonz.dk wrote: >>>>> On 22 Okt., 23:23, Joerg <inva...@invalid.invalid> wrote: >>>>>> Folks, >>>>>> Looked at Digikey and some others. Where are those huge capacitance >>>>>> varicaps? The ones with several hundred pF of range for AM radios. All >>>>>> gone lalaland by now? >>>>>> Even the ones I found in the 100pF range are either obsolete or not >>>>>> recommended for new designs. >>>>>> What I am trying to do: I need to control a switcher chip in frequency >>>>>> because I've got a very resonant load to deal with. Unfortunately it >>>>>> sets the frequency with a timing cap. I'll have to somehow vary that >>>>>> between 750pF and 2000pF. Can also be digital but then with a >>>>>> granularity of 5pF. The sawtooth voltage across it is 2.5Vpp. >>>>>> Doing it with caps and a mux chip or two has its own challenges. The >>>>>> ADG-series from AD is around 11pF per pin, otherwise their Rdson is too >>>>>> high. Talking about the a rock and a hard spot here. >>>>>> Oh, and cost is not very important. If a diode or two or three are >>>>>> needed that cost $5 a pop that's ok. >>>>>> -- >>>>>> Regards, Joerg >>>>>> http://www.analogconsultants.com/ >>>>> possible to force you own triangle in? >>>> Not on this one. It issues a major reset pulse of almost 50mA and if >>>> that sees any obstructions it all goes bonkers. It already does when you >>>> tough it with a 10k resistor, like the princess on the pea. >>>> -- >>>> Regards, Joerg >>>> http://www.analogconsultants.com/ >>> this too crazy?http://www.falstad.com/circuit/e-capmult.html >> Not crazy at all but there can't be an R3 in my case. Falls apart when >> it gets into the tens of ohms. It's sawtooth, not triangular. >> >> -- >> Regards, Joerg >> >> http://www.analogconsultants.com/ > > I'm just guessing, diode across R3 ? >No, there is more or less a wire. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●October 22, 20122012-10-22
On Oct 22, 6:27=A0pm, Joerg <inva...@invalid.invalid> wrote:> George Herold wrote: > > On Oct 22, 5:23 pm, Joerg <inva...@invalid.invalid> wrote: > >> Folks, > > >> Looked at Digikey and some others. Where are those huge capacitance > >> varicaps? The ones with several hundred pF of range for AM radios. All > >> gone lalaland by now? > > >> Even the ones I found in the 100pF range are either obsolete or not > >> recommended for new designs. > > >> What I am trying to do: I need to control a switcher chip in frequency > >> because I've got a very resonant load to deal with. Unfortunately it > >> sets the frequency with a timing cap. I'll have to somehow vary that > >> between 750pF and 2000pF. Can also be digital but then with a > >> granularity of 5pF. The sawtooth voltage across it is 2.5Vpp. > > >> Doing it with caps and a mux chip or two has its own challenges. The > >> ADG-series from AD is around 11pF per pin, otherwise their Rdson is to=o> >> high. Talking about the a rock and a hard spot here. > > >> Oh, and cost is not very important. If a diode or two or three are > >> needed that cost $5 a pop that's ok. > > >> -- > >> Regards, Joerg > > >>http://www.analogconsultants.com/ > > > Hmm.. I have no idea Joerg. > > So silly ideas, can you parallel a bunch of small ones? > > What's the frequency? =A0Could you use a cruddie Y5/Z5 ceramic? > > > (You've most likely already been down both these roads.) > > Yup :-( > > They don't make Z5U this small. Paralleling gets to be tough for space > reasons because I'd need a boatload.OK so how 'bout a few Z5U in series? George H.> > -- > Regards, Joerg > > http://www.analogconsultants.com/- Hide quoted text - > > - Show quoted text -
Reply by ●October 22, 20122012-10-22
On 23 Okt., 01:16, Joerg <inva...@invalid.invalid> wrote:> langw...@fonz.dk wrote: > > On 23 Okt., 01:08, Joerg <inva...@invalid.invalid> wrote: > >> langw...@fonz.dk wrote: > >>> On 23 Okt., 00:30, Joerg <inva...@invalid.invalid> wrote: > >>>> langw...@fonz.dk wrote: > >>>>> On 22 Okt., 23:23, Joerg <inva...@invalid.invalid> wrote: > >>>>>> Folks, > >>>>>> Looked at Digikey and some others. Where are those huge capacitance > >>>>>> varicaps? The ones with several hundred pF of range for AM radios. All > >>>>>> gone lalaland by now? > >>>>>> Even the ones I found in the 100pF range are either obsolete or not > >>>>>> recommended for new designs. > >>>>>> What I am trying to do: I need to control a switcher chip in frequency > >>>>>> because I've got a very resonant load to deal with. Unfortunately it > >>>>>> sets the frequency with a timing cap. I'll have to somehow vary that > >>>>>> between 750pF and 2000pF. Can also be digital but then with a > >>>>>> granularity of 5pF. The sawtooth voltage across it is 2.5Vpp. > >>>>>> Doing it with caps and a mux chip or two has its own challenges. The > >>>>>> ADG-series from AD is around 11pF per pin, otherwise their Rdson is too > >>>>>> high. Talking about the a rock and a hard spot here. > >>>>>> Oh, and cost is not very important. If a diode or two or three are > >>>>>> needed that cost $5 a pop that's ok. > >>>>>> -- > >>>>>> Regards, Joerg > >>>>>>http://www.analogconsultants.com/ > >>>>> possible to force you own triangle in? > >>>> Not on this one. It issues a major reset pulse of almost 50mA and if > >>>> that sees any obstructions it all goes bonkers. It already does when you > >>>> tough it with a 10k resistor, like the princess on the pea. > >>>> -- > >>>> Regards, Joerg > >>>>http://www.analogconsultants.com/ > >>> this too crazy?http://www.falstad.com/circuit/e-capmult.html > >> Not crazy at all but there can't be an R3 in my case. Falls apart when > >> it gets into the tens of ohms. It's sawtooth, not triangular. > > >> -- > >> Regards, Joerg > > >>http://www.analogconsultants.com/ > > > I'm just guessing, diode across R3 ? > > No, there is more or less a wire. >I meant add diode so discharge is fast -Lasse
Reply by ●October 22, 20122012-10-22
On Mon, 22 Oct 2012 14:22:49 -0700, Joerg <invalid@invalid.invalid> wrote:>Folks, > >Looked at Digikey and some others. Where are those huge capacitance >varicaps? The ones with several hundred pF of range for AM radios. All >gone lalaland by now? > >Even the ones I found in the 100pF range are either obsolete or not >recommended for new designs. > >What I am trying to do: I need to control a switcher chip in frequency >because I've got a very resonant load to deal with. Unfortunately it >sets the frequency with a timing cap. I'll have to somehow vary that >between 750pF and 2000pF. Can also be digital but then with a >granularity of 5pF. The sawtooth voltage across it is 2.5Vpp. > >Doing it with caps and a mux chip or two has its own challenges. The >ADG-series from AD is around 11pF per pin, otherwise their Rdson is too >high. Talking about the a rock and a hard spot here. > >Oh, and cost is not very important. If a diode or two or three are >needed that cost $5 a pop that's ok.SVC383 ex-Sanyo, is still in the ON catalog, with no product notices re last run or anything. Dual 500pf. http://www.onsemi.com/pub_link/Collateral/ENN6264-D.PDF RL
Reply by ●October 22, 20122012-10-22
krw@att.bizzzzzzzzzzzz wrote:> On Mon, 22 Oct 2012 14:22:49 -0700, Joerg <invalid@invalid.invalid> wrote: > >> Folks, >> >> Looked at Digikey and some others. Where are those huge capacitance >> varicaps? The ones with several hundred pF of range for AM radios. All >> gone lalaland by now? > > http://www.angelfire.com/electronic2/index1/VariableCap.html > > About half way down. > >> Even the ones I found in the 100pF range are either obsolete or not >> recommended for new designs. > > No kiddin? ;-) > >> What I am trying to do: I need to control a switcher chip in frequency >> because I've got a very resonant load to deal with. Unfortunately it >> sets the frequency with a timing cap. I'll have to somehow vary that >> between 750pF and 2000pF. Can also be digital but then with a >> granularity of 5pF. The sawtooth voltage across it is 2.5Vpp. > > Use a regulator with an external clock. That's what we do (all of our > switchers are synchronized). >Well, I need one from LTC because it must be simulated. The load is really ugly yet must be well regulated with some unorthodox loop elements in there. Linear only has the 3721 and 3723 for push-pull. Some older ones as well but they have the same engine type in them.>> Doing it with caps and a mux chip or two has its own challenges. The >> ADG-series from AD is around 11pF per pin, otherwise their Rdson is too >> high. Talking about the a rock and a hard spot here. >> >> Oh, and cost is not very important. If a diode or two or three are >> needed that cost $5 a pop that's ok. > > A regulator with an external clock shouldn't be an issue, then.If LTC had a suitable one. We have a processor so sync'ing is no big deal except that I usually get the looks if I request processor MIPS. Analog dudes aren't really entitled to those. Anyhow, it's not a show stopper, I can use a small varicap plus mux. The mux is like an umpteen-speed gear shifter, not very pretty. If big varicaps were still available it would become very easy. But I guess even if I found one the risk is too great that it's going to be obsoleted in a few years. -- Regards, Joerg http://www.analogconsultants.com/
