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I need programmable current control, fading from zero to 2 milliAmps. I was hoping to use Arduino's AnalogWrite(), which uses Phase Width Modulation (PWM) to simulate analog output with a sawtooth wave on a duty-cycle; to control an LM334Z to deliver a slowly ramped low current delivery. [The application is a TransCranial Direct Current Stimulation (TDCS) micro-current delivery to the human scalp. Jumping straight to 2 milliAmps is uncomfortable]. Will PWM work? Or, do I need some sort of smoothing circuitry to soften the PMW before it is applied to the LM334Z's Rset pin to accomplish the above?

  • an LED glued to the face of an LDR converts voltage to resistance, but a digital pot would be simpler to calibrate. I'm using a MCP41010 with the 334, which works very well and cost me ~$1us – dandavis Mar 5 '17 at 12:50
  • an LM317 can provide 0-2ma CC with common 1/4watt resistors, look at the datasheet. – dandavis Mar 5 '17 at 13:48
  • On Arduino, PWM stands for Pulse Width Modulation, not “Phase Width Modulation” – James Waldby - jwpat7 Mar 5 '17 at 21:47
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If you don't need super high accuracy, using a MOSFET's ohmic region, plus a smoothing filter on the output of your PWM (analog out), could be a solution.

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You control the LM334 with a resistance, not a voltage. The current is set by multiplying the current through the resistor.

Maybe you can do what you want by replacing the Rset with a digital potentiometer?

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LM334Z's Rset pin to accomplish the above?

Most of that type of circuit has its operations be determined by the current In or out of that pin. So a voltage signal may not work - you will need to experiment. I have had some success with analogs dds chips and linear programmable osscillators.

So try it on your chip. Nothin to lose.

  • since it's output current is independent of any voltage, that will not work, it needs a resistor. – dandavis Mar 5 '17 at 13:46

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