On Thu, 08 Oct 2015 08:18:55 +0100, John Devereux <john@devereux.me.uk> wrote:>John Larkin <jjlarkin@highlandtechnology.com> writes: > >> On Sat, 3 Oct 2015 20:42:59 -0400, "Tom Miller" >> <tmiller11147@verizon.net> wrote: >> >>> >>>"rickman" <gnuarm@gmail.com> wrote in message >>>news:mupjij$k5a$1@dont-email.me... >>>> On 10/3/2015 5:57 PM, Tom Miller wrote: >>>>> >>>>> "rickman" <gnuarm@gmail.com> wrote in message >>>>> news:muph5o$88r$2@dont-email.me... >>>>>> On 10/3/2015 4:58 PM, John Larkin wrote: >>>>>>> On Sat, 3 Oct 2015 11:09:40 -0700 (PDT), dagmargoodboat@yahoo.com >>>>>>> wrote: >>>>>>> >>>>>>> >>>>>>> PV optocouplers are cool for driving isolated gates, but maybe not >>>>>>> available in your junk box. >>>>>>> >>>>>>> I'm designing a kilovolt-range linear voltage regulator, and a PV is a >>>>>>> really easy way to drive the pass transistor gate. >>>>>>> >>>>>>> Hey, a packaged SIP dc/dc converter would make a nice SSR gate driver. >>>>>>> $4 or something from Mouser. >>>>>> >>>>>> That is the point of this circuit. A PV photocoupler needs a power >>>>>> source. This circuit *is* the power source. >>>>>> >>>>>> >>>>> >>>>> No, a PV optocoupler makes it own voltage. Just add it to the 12 volts >>>>> to drive the gate. >>>> >>>> Since when? They use a phototransistor, not a PV solar cell. >>>> >>>> -- >>>> >>>> Rick >>> >>>I guess that's why they call them PV optocouplers. >> >> A phototransistor optocoupler will generate a little voltage on the >> output side, not enough to be useful for anything I can imagine. > >Maybe the trick of generating a negative bias current to pull an opamp >output down though ground?Something like that, where you need a half a volt of negative voltage and don't want a charge pump or anything like that. We use some cool Ixys self-protecting SSRs as current limiters, where we don't need either isolation or switching. The PV optocouplers are under 1% efficient. Lots of other uses would appear for one that was, say, 10%. More than that would be difficult.
A very silly circuit
Started by ●October 3, 2015
Reply by ●October 8, 20152015-10-08
Reply by ●October 8, 20152015-10-08
On 08/10/2015 08:18, John Devereux wrote:> John Larkin <jjlarkin@highlandtechnology.com> writes:>> A phototransistor optocoupler will generate a little voltage on the >> output side, not enough to be useful for anything I can imagine. > > Maybe the trick of generating a negative bias current to pull an opamp > output down though ground? >You don't even need an opto-coupler for that. As Pease wrote: just use a 2N2222 (or similar) with base grounded, zener the emitter junction with plenty mA and see a small negative voltage at the collecter. The B-E zener emits light that excites the B-C junction as a photodiode. piglet
Reply by ●October 8, 20152015-10-08
piglet wrote:> You don't even need an opto-coupler for that. As Pease wrote: just use a > 2N2222 (or similar) with base grounded, zener the emitter junction with > plenty mA and see a small negative voltage at the collecter. The B-E > zener emits light that excites the B-C junction as a photodiode.Since it's not April, the 1st, so.. please explain. :-) Best regards, Piotr
Reply by ●October 8, 20152015-10-08
On 08/10/2015 16:46, Piotr Wyderski wrote:> piglet wrote: > >> You don't even need an opto-coupler for that. As Pease wrote: just use a >> 2N2222 (or similar) with base grounded, zener the emitter junction with >> plenty mA and see a small negative voltage at the collecter. The B-E >> zener emits light that excites the B-C junction as a photodiode. > > Since it's not April, the 1st, so.. please explain. :-) > > Best regards, Piotr >I thought my description did explain it. Go on, try it: <https://www.dropbox.com/s/g9zwy6wyb4lhx4a/peasecon.pdf> Have fun. piglet
Reply by ●October 8, 20152015-10-08
On Thursday, October 8, 2015 at 11:59:16 AM UTC-4, piglet wrote:> On 08/10/2015 16:46, Piotr Wyderski wrote: > > piglet wrote: > > > >> You don't even need an opto-coupler for that. As Pease wrote: just use a > >> 2N2222 (or similar) with base grounded, zener the emitter junction with > >> plenty mA and see a small negative voltage at the collecter. The B-E > >> zener emits light that excites the B-C junction as a photodiode. > > > > Since it's not April, the 1st, so.. please explain. :-) > > > > Best regards, Piotr > > > > I thought my description did explain it. Go on, try it: > > <https://www.dropbox.com/s/g9zwy6wyb4lhx4a/peasecon.pdf> > > Have fun. > > pigletWeird, I got -0.37V with a 3904, but 10 k ohm load killed it, 100k ohm and it fell to ~ -0.037. George H.
Reply by ●October 8, 20152015-10-08
On 08/10/2015 17:07, George Herold wrote:> Weird, I got -0.37V with a 3904, but 10 k ohm load killed it, > 100k ohm and it fell to ~ -0.037. > > George H. >Yeah, power conversion efficiency is terrible but that can be OK if you only need a micro-amp. I believe someone has used this as a way of getting a few tens of millivolts for op-amp offset nulling! Watch out how you use the transistor after your experiment, the sustained Veb breakdown will have reduced beta and increased noise. I tried this again just now and initial beta of 553 fell to 525 after jsut one minute of experiment. piglet
Reply by ●October 8, 20152015-10-08
piglet <erichpwagner@hotmail.com> writes:> On 08/10/2015 08:18, John Devereux wrote: >> John Larkin <jjlarkin@highlandtechnology.com> writes: > >>> A phototransistor optocoupler will generate a little voltage on the >>> output side, not enough to be useful for anything I can imagine. >> >> Maybe the trick of generating a negative bias current to pull an opamp >> output down though ground? >> > > You don't even need an opto-coupler for that. As Pease wrote: just use > a 2N2222 (or similar) with base grounded, zener the emitter junction > with plenty mA and see a small negative voltage at the collecter. The > B-E > zener emits light that excites the B-C junction as a photodiode.That's a new one on me. I imagine that is even less efficient! -- John Devereux
Reply by ●October 8, 20152015-10-08
On Thursday, October 8, 2015 at 11:59:16 AM UTC-4, piglet wrote:> On 08/10/2015 16:46, Piotr Wyderski wrote: > > piglet wrote: > > > >> You don't even need an opto-coupler for that. As Pease wrote: just use a > >> 2N2222 (or similar) with base grounded, zener the emitter junction with > >> plenty mA and see a small negative voltage at the collecter. The B-E > >> zener emits light that excites the B-C junction as a photodiode. > > > > Since it's not April, the 1st, so.. please explain. :-) > > > > Best regards, Piotr > > > > I thought my description did explain it. Go on, try it: > > <https://www.dropbox.com/s/g9zwy6wyb4lhx4a/peasecon.pdf> > > Have fun. > > piglethttp://electronicdesign.com/site-files/electronicdesign.com/files/archive/electronicdesign.com/files/29/6362/figure_01.gif Applied for bias cancellation... http://electronicdesign.com/analog/single-supply-op-amp-input-bias-current-cancellation Cheers, James Arthur
Reply by ●October 8, 20152015-10-08
On Thu, 8 Oct 2015 09:59:55 -0700 (PDT), dagmargoodboat@yahoo.com wrote:>On Thursday, October 8, 2015 at 11:59:16 AM UTC-4, piglet wrote: >> On 08/10/2015 16:46, Piotr Wyderski wrote: >> > piglet wrote: >> > >> >> You don't even need an opto-coupler for that. As Pease wrote: just use a >> >> 2N2222 (or similar) with base grounded, zener the emitter junction with >> >> plenty mA and see a small negative voltage at the collecter. The B-E >> >> zener emits light that excites the B-C junction as a photodiode. >> > >> > Since it's not April, the 1st, so.. please explain. :-) >> > >> > Best regards, Piotr >> > >> >> I thought my description did explain it. Go on, try it: >> >> <https://www.dropbox.com/s/g9zwy6wyb4lhx4a/peasecon.pdf> >> >> Have fun. >> >> piglet > >http://electronicdesign.com/site-files/electronicdesign.com/files/archive/electronicdesign.com/files/29/6362/figure_01.gif > >Applied for bias cancellation... >http://electronicdesign.com/analog/single-supply-op-amp-input-bias-current-cancellation > >Probably noisy. And maybe drifty. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●October 8, 20152015-10-08
On Thursday, October 8, 2015 at 1:19:50 PM UTC-4, John Larkin wrote:> On Thu, 8 Oct 2015 09:59:55 -0700 (PDT), dagmargoodboat@yahoo.com > wrote: > > >On Thursday, October 8, 2015 at 11:59:16 AM UTC-4, piglet wrote: > >> On 08/10/2015 16:46, Piotr Wyderski wrote: > >> > piglet wrote: > >> > > >> >> You don't even need an opto-coupler for that. As Pease wrote: just use a > >> >> 2N2222 (or similar) with base grounded, zener the emitter junction with > >> >> plenty mA and see a small negative voltage at the collecter. The B-E > >> >> zener emits light that excites the B-C junction as a photodiode. > >> > > >> > Since it's not April, the 1st, so.. please explain. :-) > >> > > >> > Best regards, Piotr > >> > > >> > >> I thought my description did explain it. Go on, try it: > >> > >> <https://www.dropbox.com/s/g9zwy6wyb4lhx4a/peasecon.pdf> > >> > >> Have fun. > >> > >> piglet > > > >http://electronicdesign.com/site-files/electronicdesign.com/files/archive/electronicdesign.com/files/29/6362/figure_01.gif > > > >Applied for bias cancellation... > >http://electronicdesign.com/analog/single-supply-op-amp-input-bias-current-cancellation > > > > > > Probably noisy. And maybe drifty.Dunno. Zeners are still lower noise than band-gaps, right? Woodward's one of the best, but it has been eighteen years since he wrote that. And he was souping up what is basically a high-test LM324, so it just might not matter that much. www.linear.com/product/LT1013 Cheers, James Arthur
