Current sources for load referred to ground. - Page 1
Forum section: electronics / projects

author: atferrari
author_rank: Frequent Contributor
timestamp: November 26, 2014, 08:56:14 pm
content: After reading about constant current sources, I defined the four cases shown in the pdf. Current should go up to 250 mA.Implementing B and C with the attached circuit (and its counterpart) is straightforward, but I am not sure how to proceed for A and D. I cannot have Rsense referred to ground anymore.How could I go away with no fancy ICs?Gracias for any help.Please eliminate .txt extension to open the .asc file.

author: atferrari
author_rank: Frequent Contributor
timestamp: November 30, 2014, 07:40:07 pm
content: Quote from: DiligentMinds.com on November 30, 2014, 06:29:36 pmGracias for replying, Ken.Simple constant current source, adjustable up to 250 mA (or maybe just 100 mA). Steady current for simple tests at the bench to avoid wiring up one every time I need one.Not programmable, just adjustable.I realized that I can have Rsense referred to +V (or -V) as in cases B or C, I had it referred to ground.Basically my problem is solved.

author: Kevin.D
author_rank: Frequent Contributor
timestamp: November 30, 2014, 08:53:07 pm
content: Quote from: atferrari on November 30, 2014, 07:40:07 pmHiIf your making your sink/source battery powered or powering it from it's own independant supply like you will be doing if it's a piece of bench test equipment your making, then it doesn't matter where your inserting it into in the DUT circuit, weather it's on the high side (Sourcing) of the DUT or on the low side of the DUT (Sinking) makes no difference, it's still only measuring and controlling the current going through it relative to it's own GND. So a standard NPN or NFET (along the lines of the one in your '.asc' but using NFET is better than BJT) type source/sink does all 4 of your scenarious.(it still needs to be inserted with the correct polarity of course)Regards

author: Marco
author_rank: Super Contributor
timestamp: November 30, 2014, 08:54:11 pm
content: LED+single transistor current sources, you almost certainly already have everything necessary available.This is the high side one, the low side one uses a NPN.

author: dannyf
author_rank: Super Contributor
timestamp: November 30, 2014, 09:52:25 pm
content: Easy:1) use a two terminal device, like a constant current diode / jfet;2) use set-ups that are referenced to the high side....

author: void_error
author_rank: Frequent Contributor
timestamp: November 30, 2014, 11:15:28 pm
content: Quote from: Marco on November 30, 2014, 08:54:11 pm330 ohm resistor... 15V supplyI see Magic Smoke Emitting Diode here, or transistor depending on the value of Re.Replace the LED with two 1N4148s and increase the 330ohm resistor to 1.5k... ish.

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: December 01, 2014, 11:14:47 am
content: http://waltjung.org/PDFs/Sources_101_P1.pdfhttp://waltjung.org/PDFs/Sources_101_P2.pdfthe LM317 CCS is especially simple, cheap, high enough current and power rated

author: atferrari
author_rank: Frequent Contributor
timestamp: December 01, 2014, 05:47:02 pm
content: Quote from: Kevin.D on November 30, 2014, 08:53:07 pmRevising my design in that directionThanks for reminding me that!

author: atferrari
author_rank: Frequent Contributor
timestamp: December 01, 2014, 05:47:51 pm
content: Quote from: f5r5e5d on December 01, 2014, 11:14:47 amThanks for those .pdf.

author: atferrari
author_rank: Frequent Contributor
timestamp: December 01, 2014, 05:48:46 pm
content: Quote from: DiligentMinds.com on December 01, 2014, 02:08:19 amHere, that IC is "fancy" type. Thanks anyway for replying.

author: atferrari
author_rank: Frequent Contributor
timestamp: December 01, 2014, 05:50:31 pm
content: Quote from: Marco on November 30, 2014, 08:54:11 pmConsidering how far I could go with it (adjustable up to 250 mA) (?)