I think this works. https://www.dropbox.com/scl/fi/kbfnta8idc9f8o3ww6zt6/Current_Sink_3.jpg?rlkey=06hl3vdh8eataurw8cf5l7dor&raw=1
current sink
Started by ●December 20, 2023
Reply by ●December 21, 20232023-12-21
On 21/12/2023 2:52 pm, John Larkin wrote:> I think this works. > > https://www.dropbox.com/scl/fi/kbfnta8idc9f8o3ww6zt6/Current_Sink_3.jpg?rlkey=06hl3vdh8eataurw8cf5l7dor&raw=1It might, if you picked the right op amp. Only a limited number work with their inputs at the negative supply voltage. Until you identify the op amp, it's a less-than-useful insight. -- Bill Sloman, Sydney
Reply by ●December 21, 20232023-12-21
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=1Cool!
Reply by ●December 21, 20232023-12-21
One downside of that design is when you use the power pin like that you have to use a dedicated part, which means you can't use it with quads and duals.
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 > > >Yes, clever - within the limits on range, compliance voltage and stability should work. -- piglet
Reply by ●December 21, 20232023-12-21
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=1Cool! PS there are of course severe limitations with that circuit. 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
Reply by ●December 21, 20232023-12-21
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=1That 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.
Reply by ●December 21, 20232023-12-21
piglet <erichpwagner@hotmail.com> wrote:> https://www.dropbox.com/scl/fi/kbfnta8idc9f8o3ww6zt6/Current_Sink_3.jpg?r > lkey=06hl3vdh8eataurw8cf5l7dor&raw=1I see no advantage over conventional methods, in fact, several disadvantages. Why waste our time on ideas that have no merit? -- MRM
Reply by ●December 21, 20232023-12-21
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. I actually have a use for this. Sorry to waste your valuable time. How much do you charge per hour, to read usenet posts?
Reply by ●December 21, 20232023-12-21
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.
