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  • IC Question

    I'm looking to simulate for 0 - 20 ma signal for making a simple I/O board to test some programs.
    My analog card has a 50ohm input resistance so i need to regulate the current going into the analog card. This is pretty easy if it was just one input i need to simulate. Just use a 1.5v battery with some resistor. However i need to simulate 4 input so a resistor network wouldn't work because if i change one current i'll affect the other 3. So IC guru could you please point me to the right chip that will enable me to regulate and adjust 4 independent current loop using 24V input. I would like some sort of current limiting feature so i won't go over 20 ma. Also would like to adjust using some sort of resistor pot that will give reasonable accurately between 0 and 20mA at 1 or 2 mA increments.
    Any help is greatly appreciated

  • #2
    I think you're best bet is just resistors and switches if it's just for temporary use. Unless you want to spend some money on a high end power supply or build one.

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    • #3
      if you mean the 24 input voltage regulator as the power supply, i already have that, a very good one as well.

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      • #4
        Well, here's an example of a variable limiter and some explanation.
        http://www.radio-electronics.com/inf...nt_limiter.php

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        • #5
          will look into this! thanks for the info!

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          • #6
            looked awfully like the current mirror circuit, that i learned a while back in school.
            time to crack out the textbook.
            i was hoping it would be in a simple IC package like the lm377, except i don't think the lm377 does exactly what i want.

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            • #7
              I think that feedback method will be the simplest. Check out the LM2673. It has adjustable current limit, but it's an entire switching supply. That's probably the only type of chip solution you'll find.

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              • #8
                LM2673 wouldn't work since the current limit range is not even near the mA area.

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                • #9
                  so nevermind, i found 0 - 20 ma optical rotary encoder that'll do what i want.
                  it'll be easier than trying to pick up circuit stuff again.
                  thanks for the help curiosty!

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                  • #10
                    Sorry, I should have looked at the datasheet. Nice find on the rotary encoder. That could make for an interesting input device as well.

                    I also found the L200C, which might have worked for V and A control.
                    http://www.zen22142.zen.co.uk/Circuits/Power/l200.html
                    Although the example is 100mA min, the datasheet shows much lower.

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                    • #11
                      looking at the datasheet, the area where Io is less than 100ma seems is sloped very steep, which mean it may be hard to have precise control. I'll have a closer look at this circuit when i get a chance.

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                      • #12
                        Yeah, it does seem a bit curved at the low end. What I was thinking of was lipo chargers in small devices such as bluetooth headsets and such. I'm sure they use designs like that but on a smaller scale. Here's a more linear one using an op-amp.
                        http://www.elecfree.com/electronic/c...to-2a-by-l200/
                        The components just keep adding up.

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                        • #13
                          haha, the beauty of IC, anything is possible, just add more stuff.
                          Thats enough for a small little PBC board lol.

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