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I am trying to create a constant current output for my project between 0 - 10 mA.

I read we can convert voltage to current by using op amp http://www.allaboutcircuits.com/textbook/semiconductors/chpt-8/voltage-to-current-signal-conversion/

but I also found IC http://www.ti.com/lit/ds/symlink/xtr110.pdf

so for voltage current conversion do I have to use a IC like xtr110 or can I just use a op amp?

Also, xtr110 seems to only output 4-20 mA, is there a IC that can output 0-10 mA?

My output signal is 5-30v square wave and I am trying to convert to 0-10 mA.

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  • \$\begingroup\$ you can configure that chip for a 0-20mA range. \$\endgroup\$ – Vladimir Cravero Jun 5 '15 at 8:04
  • \$\begingroup\$ Do you want a positive rail sourced current or a negative sink. \$\endgroup\$ – Andy aka Jun 5 '15 at 8:35
  • \$\begingroup\$ can you clarify what those terms are? sorry I am new to electronics \$\endgroup\$ – kevin0228ca Jun 5 '15 at 8:54
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XTR110 is a specialty IC designed for use in industrial environments, where 4 to 20mA currents are a common way to communicate analog values between industrial modules. It can be configured for a variety of output currents, including 0 to 10mA. Internally, it's implemented much the same way as an opamp solution, as shown by its schematic diagram in the datasheet.

Whether you use this IC, one like it, or implement it yourself using opamps, depends on your precision requirements, your budget, and other design constraints.

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  • \$\begingroup\$ I see. so if I have budget and am new to electronics, maybe I should get the IC. Is there any drawback regarding using IC? or is there anything I should keep in mind when using IC? \$\endgroup\$ – kevin0228ca Jun 5 '15 at 8:58
  • \$\begingroup\$ @kevin0228ca That really depends on the details of your application and your requirements, which you haven't disclosed. \$\endgroup\$ – Nick Johnson Jun 5 '15 at 9:14
  • \$\begingroup\$ I am developing a nerve stimulation system, so I assume if I keep current < 10 mA by using IC since max is 20 mA, no harm should be induced. \$\endgroup\$ – kevin0228ca Jun 5 '15 at 9:57
  • \$\begingroup\$ I suspect an opamp configured as a transconductance amplifier will suit you just fine in that application. \$\endgroup\$ – Nick Johnson Jun 5 '15 at 10:02
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You can use a two-terminal current regulator such as an LM317LZ (TO-92 package). That and one resistor (add an adjustable resistor if you want to trim it).

enter image description here

The output current is approximately 1.25V/R so for about 10mA you'd use 125 ohms. You could use a 100 ohm resistor and a 50 ohm pot for R1/R2 to trim it.

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