Simple! Since it's AC, tack on a transformer to step it up by an arbitrary ratio. You now have AC of suitable voltage, to drive any conventional circuit, or to use directly if it's of the right frequency already. ;-) Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com "Piotr Wyderski" <no@mail.com> wrote in message news:o3th89$m4e$1@node1.news.atman.pl...> If the power supply voltage is high, say >=3V, it is pretty simple > to design an oscillator (of unimportant output frequency and shape), > which can be powered from an AC power source: just add a diode bridge > at the power input lines and use any suitable DC-powered oscillator > circuit. But what if the supply voltage is really low, say 0.2V? > JFET-based oscillators can go really low, allegedly down to 25mV, > so it should be possible to pair two of them anti-paralelly and > power them directly from AC. However, the JFET structure exhibits > a high degree of symmetry, i.e. the D and S pins are called so > by convention and the device can work in "inversion mode". Is > it possible to use this fact to build an AC-powered oscillator > with a single JFET? > > Best regards, Piotr
Low-voltage AC-powered oscillator
Started by ●December 27, 2016
Reply by ●December 28, 20162016-12-28
Reply by ●December 28, 20162016-12-28
On 12/27/2016 11:59 PM, Tim Williams wrote:> Simple! > > Since it's AC, tack on a transformer to step it up by an arbitrary > ratio. You now have AC of suitable voltage, to drive any conventional > circuit, or to use directly if it's of the right frequency already. > > ;-) > > Tim >Hi Piotr, I saw this oscillator that will run on well under 20mV, and thought maybe it would be of interest to you. http://www.dicks-website.eu/fetosc/enindex.htm Mikek --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus
Reply by ●December 28, 20162016-12-28
On Tuesday, December 27, 2016 at 1:00:07 PM UTC-5, Steve Wilson wrote:> Piotr Wyderski <no@mail.com> wrote: > > > If the power supply voltage is high, say >=3V, it is pretty simple > > to design an oscillator (of unimportant output frequency and shape), > > which can be powered from an AC power source: just add a diode bridge > > at the power input lines and use any suitable DC-powered oscillator > > circuit. But what if the supply voltage is really low, say 0.2V? > > JFET-based oscillators can go really low, allegedly down to 25mV, > > so it should be possible to pair two of them anti-paralelly and > > power them directly from AC. However, the JFET structure exhibits > > a high degree of symmetry, i.e. the D and S pins are called so > > by convention and the device can work in "inversion mode". Is > > it possible to use this fact to build an AC-powered oscillator > > with a single JFET? > > > > Best regards, Piotr > > > > This is not what you asked, but the LTC3108 uses a MOSFET and operates down > to 20mV: > > http://www.linear.com/product/LTC3108 > > So it can be done and is available commercially.That's pretty neat. Surveying that and several JFET equivalent circuits out there, they all seem to consist of blocking oscillators featuring a depletion-mode switch. Cheers, James Arthur
Reply by ●December 31, 20162016-12-31
On 28/12/16 07:14, Jim Thompson wrote:> On Tue, 27 Dec 2016 12:10:17 -0700, Jim Thompson > <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: > >> On Tue, 27 Dec 2016 13:36:17 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 12/27/2016 01:27 PM, Jim Thompson wrote: >>>> On Tue, 27 Dec 2016 12:32:50 -0500, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> On 12/27/2016 12:27 PM, Jim Thompson wrote: >>>>>> On Tue, 27 Dec 2016 17:47:46 +0100, Piotr Wyderski >>>>>> <peter.pan@neverland.mil> wrote: >>>>>> >>>>>>> Phil Hobbs wrote: >>>>>>> >>>>>>>> Doesn't fix the polarization of the FET. It won't amplify if you come >>>>>>>> in via the drain. >>>>>>> >>>>>>> I'm afraid I don't understand what you mean, Phil. The only polarization >>>>>>> in a JFET I know of is the polarization of the gate diode, which is a >>>>>>> P region somehow embedded within the N silicon bar which makes up D and >>>>>>> S. Drain is the end with higher potential and source with the lower, but >>>>>>> it flips as the AC waveform changes. Is it correct? >>>>>>> >>>>>>> Do you mean the problems with *external* gate polarization circuitry, >>>>>>> which would inject current through the gate if powered incorrectly? >>>>>>> >>>>>>> Best regards, Piotr >>>>>>> >>>>>>> >>>>>> >>>>>> Phil only thinks discrete devices which (usually) have back >>>>>> gate/substrate tied to source. In my I/C world it's trivial to have >>>>>> both gates independent, so a _symmetrical_ grounded-gate situation is >>>>>> quite possible. >>>>>> >>>>>> (I am currently working with a major ASIC foundry to get a good JFET >>>>>> structure added to their repertoire.) >>>>>> >>>>>> ...Jim Thompson >>>>>> >>>>> >>>>> The voltage gradient along the channel is what makes the drain different >>>> >from the source, even in a perfectly symmetrical FET. (These exist in >>>>> discretes, e.g. the BF862.) >>>>> >>>>> Inverting the supply in a common-gate amplifier moves the pinch from one >>>>> end of the channel to the other, effectively interchanging drain and >>>>> source. It'll amplify one way, but not the other. >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>> >>>> Wrong >:-} >>>> >>>> ...Jim Thompson >>>> >>> Show your work. >>> >>> Cheers >>> >>> Phil Hobbs >> >> <http://www.analog-innovations.com/SED/PJFET_Construction.pdf> >> >> Which is drain and which is source is determined by potential >> direction... in this (PJFET) case drain is defined by the source/drain >> terminal that is negative relative to the other terminal. >> >> ...Jim Thompson > > Presently under analysis for practicality... > > <http://www.analog-innovations.com/SED/Circular_JFET.pdf>How many process step required to make that? More than the simple JFET, I presume...
