On Thu, 21 Dec 2023 03:51:20 -0800 (PST), Fred Bloggs <bloggs.fredbloggs.fred@gmail.com> wrote:>On Wednesday, December 20, 2023 at 10:53:15?PM UTC-5, John Larkin wrote: >> I think this works. >> >> https://www.dropbox.com/scl/fi/kbfnta8idc9f8o3ww6zt6/Current_Sink_3.jpg?rlkey=06hl3vdh8eataurw8cf5l7dor&raw=1 > > >That goes back a ways. You'll find examples of that in the older opamp cookbooks circa 1970s-1980s -ish. Disadvantage is it requires a single OA pkg, also I has to be in excess of OA supply current. Other than that it's a perfectly good circuit.I hadn't seen it before, but I guess most simple circuits have been discovered before, somewhere. What's relatively new is fabulous cheap low-current RRIO opamps.
current sink
Started by ●December 20, 2023
Reply by ●December 21, 20232023-12-21
Reply by ●December 21, 20232023-12-21
John Larkin <jl@997PotHill.com> wrote:> I think this works. > > https://www.dropbox.com/scl/fi/kbfnta8idc9f8o3ww6zt6/Current_Sink_3.jpg?rlkey=06hl3vdh8eataurw8cf5l7dor&raw=1 > > >Fun! Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
Reply by ●December 21, 20232023-12-21
torsdag den 21. december 2023 kl. 04.53.15 UTC+1 skrev John Larkin:> I think this works. > > https://www.dropbox.com/scl/fi/kbfnta8idc9f8o3ww6zt6/Current_Sink_3.jpg?rlkey=06hl3vdh8eataurw8cf5l7dor&raw=1https://www.edn.com/op-amp-can-source-or-sink-current/
Reply by ●December 21, 20232023-12-21
John Larkin wrote:> Fred Bloggs wrote: >> John Larkin wrote: >>> >>> I think this works. >>> >>> https://www.dropbox.com/scl/fi/kbfnta8idc9f8o3ww6zt6/Current_Sink_3.jpg?rlke >> >>That goes back a ways. You'll find examples of that in the older opamp cookboo > > I hadn't seen it before, but I guess most simple circuits have been > discovered before, somewhere. What's relatively new is fabulous cheap > low-current RRIO opamps.My 1963 "Handbook of Operational Amplifier Applications" by Burr-Brown shows this current source: <https://crcomp.net/misc/currentsource.png> Regardless, your own variation is also interesting. Danke, -- Don, KB7RPU, https://www.qsl.net/kb7rpu There was a young lady named Bright Whose speed was far faster than light; She set out one day In a relative way And returned on the previous night.
Reply by ●December 21, 20232023-12-21
On Thu, 21 Dec 2023 09:04:10 -0800 (PST), Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:>torsdag den 21. december 2023 kl. 04.53.15 UTC+1 skrev John Larkin: >> I think this works. >> >> https://www.dropbox.com/scl/fi/kbfnta8idc9f8o3ww6zt6/Current_Sink_3.jpg?rlkey=06hl3vdh8eataurw8cf5l7dor&raw=1 > > >https://www.edn.com/op-amp-can-source-or-sink-current/Circuits a and b have errors from the opamp supply current.
Reply by ●December 21, 20232023-12-21
On 22/12/2023 12:18 am, John Larkin wrote:> On Thu, 21 Dec 2023 12:07:58 -0000 (UTC), Mike Monett VE3BTI > <spamme@not.com> wrote: > >> piglet <erichpwagner@hotmail.com> wrote: >> >>> https://www.dropbox.com/scl/fi/kbfnta8idc9f8o3ww6zt6/Current_Sink_3.jpg?r >>> lkey=06hl3vdh8eataurw8cf5l7dor&raw=1 >> >> I see no advantage over conventional methods, in fact, several disadvantages. >> >> Why waste our time on ideas that have no merit? > > You and Sloman poison ideas at birth. There's a simple explanation.Only bad ideas, but you do seem to produce a lot of them.> I actually have a use for this.Sure you do. But you could (and should) have been more specific about which op amp you had in mind.> Sorry to waste your valuable time. How much do you charge per hour, to > read usenet posts?Nobody gets paid for reading usenet posts. Sometimes it is an educational exercise, for some people - not you, obviously - and thus an investment. -- Bill Sloman, Sydney
Reply by ●December 22, 20232023-12-22
On 22/12/2023 12:23 am, John Larkin wrote:> On Thu, 21 Dec 2023 11:43:58 GMT, Jan Panteltje <alien@comet.invalid> > wrote: > >> On a sunny day (Wed, 20 Dec 2023 19:52:11 -0800) it happened John Larkin >> <jl@997PotHill.com> wrote in <sgd7oipj183untsh2m5fa6qgle7i5v8ste@4ax.com>: >> >>> I think this works. >>> >>> https://www.dropbox.com/scl/fi/kbfnta8idc9f8o3ww6zt6/Current_Sink_3.jpg?rlkey=06hl3vdh8eataurw8cf5l7dor&raw=1 >> >> Cool! >> >> PS >> there are of course severe limitations with that circuit. > > As with every circuit. You'd need help from an engineer to make it > work. > > >> Often one need very low currents, the own current draw of the opamp or >> whatever gets then in the way >> And sometimes one needs a lot of current, more than the opamp can supply. >> So one then uses for example a 'transistor' >> https://en.m.wikipedia.org/wiki/Transistor >> the transistor / MOSFET then is driven by the amplifier. >> http://www.learningaboutelectronics.com/Articles/Current-source-circuit.php >> >> If it just needs to be sort of a constant current a simple JFET with source resistor and gate to ground will do. >> like J2 here: >> https://panteltje.online/panteltje/scope_tv/diagram.jpg > > I want a precision controlled current sink. > > Jfets have a huge range of Idss. Some parts are specified 10:1. The > Supertex depletion mosfets are much better.You use an op amp to monitor the current going through the jfet, and let the op amp output adjust the gate voltage to get the right current. You do need to design the circuit so that the op-amp output can swing far enough to cope with the worst case jfet - at either end of the range - but that's just worst-case design, and most of us seem to know about that. -- Bill Sloman, Sydney
Reply by ●December 22, 20232023-12-22
On Thursday, December 21, 2023 at 8:27:51 AM UTC-5, John Larkin wrote:> On Thu, 21 Dec 2023 03:51:20 -0800 (PST), Fred Bloggs > <bloggs.fred...@gmail.com> wrote: > >On Wednesday, December 20, 2023 at 10:53:15?PM UTC-5, John Larkin wrote: > >> I think this works. > >> > >> https://www.dropbox.com/scl/fi/kbfnta8idc9f8o3ww6zt6/Current_Sink_3.jpg?rlkey=06hl3vdh8eataurw8cf5l7dor&raw=1 > > > > > >That goes back a ways. You'll find examples of that in the older opamp cookbooks circa 1970s-1980s -ish. Disadvantage is it requires a single OA pkg, also I has to be in excess of OA supply current. Other than that it's a perfectly good circuit. > I hadn't seen it before, but I guess most simple circuits have been > discovered before, somewhere. What's relatively new is fabulous cheap > low-current RRIO opamps.There was a WH thread about 20 years ago where he used exactly this method for a current source. There were other things going in the circuit about which I'm not recalling the details.
