Current sources for load referred to ground.

[atferrari]

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.

[atferrari]

"How could I go away with no fancy ICs?"

Well, you can't if you want to do things properly.

You never mentioned what this is for.  How fast does the current source need to be [is it going to have to rapidly respond to load changes, or is it working at DC, or...]  Does it need to be adjustable, or is there one set value? Is it a V-to-I converter?  How accurate and linear does it have to be?  Are you trying to drive more than 1A, or less than 1mA?  Does it have to be extremely stable with temperature change?  Does it have to be extremely stable over time?  The answers to these questions will influence how the current source is implemented.

Perhaps you could figure out what a "Good Enough" set of specifications might be for the application that you are using this current source in, and post that, then I might be able to help with some relevant design information.

-Ken

Gracias 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.

[Kevin.D]

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.

Hi
If 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

[Marco]

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.

[dannyf]

Easy:

1) use a two terminal device, like a constant current diode / jfet;
2) use set-ups that are referenced to the high side.
...

[void_error]

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.

330 ohm resistor... 15V supply
I see Magic Smoke Emitting Diode here, or transistor depending on the value of R_e.
Replace the LED with two 1N4148s and increase the 330ohm resistor to 1.5k... ish.

[f5r5e5d]

http://waltjung.org/PDFs/Sources_101_P1.pdf

http://waltjung.org/PDFs/Sources_101_P2.pdf

the LM317 CCS is especially simple, cheap, high enough current and power rated

[atferrari]

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.

Hi
If 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

Revising my design in that direction

Thanks for reminding me that!

[atferrari]

http://waltjung.org/PDFs/Sources_101_P1.pdf

http://waltjung.org/PDFs/Sources_101_P2.pdf

the LM317 CCS is especially simple, cheap, high enough current and power rated

Thanks for those .pdf.

[atferrari]

"How could I go away with no fancy ICs?"

Well, you can't if you want to do things properly.

You never mentioned what this is for.  How fast does the current source need to be [is it going to have to rapidly respond to load changes, or is it working at DC, or...]  Does it need to be adjustable, or is there one set value? Is it a V-to-I converter?  How accurate and linear does it have to be?  Are you trying to drive more than 1A, or less than 1mA?  Does it have to be extremely stable with temperature change?  Does it have to be extremely stable over time?  The answers to these questions will influence how the current source is implemented.

Perhaps you could figure out what a "Good Enough" set of specifications might be for the application that you are using this current source in, and post that, then I might be able to help with some relevant design information.

-Ken

Gracias 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.

I would just use an LT3080 in TO-220 package, wired up as an adjustable current source [see the data sheet and relevant ap-notes for more information].  If you wanted to, you could even place another LT3080 wired up as an adjustable voltage reference in front of the LT3080 wired as an adjustable current source.  This would allow you to adjust the "compliance voltage" of your current source.  By reversing the roles [put the adjustable current source in front of the adjustable voltage source], and now you have a simple adjustable lab power supply with adjustable current limiting...

Here, that IC is "fancy" type. Thanks anyway for replying.

[atferrari]

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.

Considering how far I could go with it (adjustable up to 250 mA) (?)