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I'm trying to make constant current with a sine pulse as an assignment from my project supervisor, the problem is I really can't imagine what a constant current that has a sine pulse at all, it just sounds really confusing to me. However, after reading a bunch of research, i popped an idea of feeding constant current into the source pin of a logic mosfet, then controlled it with a digital sine pulse from a microcontroller. I don't really know that would it work or not, i would really appreciate any suggestion from u guys. I have really limited knowledge about circuit and electronics, thank you in advanced for your contribution.

I'd like to add a post that helped me think of this idea, I do recognise some problem of the circuit in this, but I'm willingly to try it out (MULTISIM) Feeding sine wave into MOSFET - Getting modified sine wave on drain For clarification, I'm making a TENS prototype device based by a microcontroller, current level should be around 5mA to 10mA, frequency ranging 50Hz to 100H and voltage can reach up to 36V if needed ( don't worry about the safety of user, I'll test it on a resistor (indicate for human impedance) first
Looks like the constant current fed into the MOSFET drain pin is a bad idea.

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  • \$\begingroup\$ Some example waveforms would be greatly appreciated. \$\endgroup\$ Commented Apr 6 at 7:31
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    \$\begingroup\$ Constant current and varying waveform are incompatible. \$\endgroup\$ Commented Apr 6 at 8:03
  • \$\begingroup\$ Do you mean a controlled current source, delivering a sine pulse of current? \$\endgroup\$ Commented Apr 6 at 8:58
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    \$\begingroup\$ Can you post (a translation of?) the actual instructions you received for this assignment? \$\endgroup\$ Commented Apr 6 at 9:25
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    \$\begingroup\$ "I don't really understand what my instructor means either". That's why we need to see the original specification / instruction / question. We can interpret it for you. Your question doesn't mention TENS which is a very important detail. Edit your question to add more information. Don't bury it in the comments. \$\endgroup\$ Commented Apr 6 at 12:58

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You can feed the constant current source with sine signal, so there will be a sine modulated across the load.
Since the 1k Load resistor is a linear device the sine will be seen in its current and voltage also.
In this schematic the sine needs to be all positive, like 400mV sine shifted to 500mV.
There is an option to build a true bipolar current source with dual supply, that can both sink and source the current.

enter image description here

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  • \$\begingroup\$ where do i input both sine signal and constant current source in this, I don't really understand this yet. \$\endgroup\$ Commented Apr 7 at 5:36
  • \$\begingroup\$ @17TrịnhHữuPhúc There is just one input for sine. Every single time interval this circuit sets the load current according input sine (its Instantaneous voltage v(t).) \$\endgroup\$ Commented Apr 7 at 9:49
  • \$\begingroup\$ Oke, I will try it out. Can I have the formula for the current so I can adjust it? \$\endgroup\$ Commented Apr 7 at 14:40
  • \$\begingroup\$ @17TrịnhHữuPhúc The formula for load current is I_load = V_sine/R_emitter, so when the input is at 500mV (sine zero cross) the load current is 5mA. When the input is at 900mV (sine in maximum) the load current is 9mA. At sine minimum it’s a 1mA. \$\endgroup\$ Commented Apr 7 at 14:53
  • \$\begingroup\$ But then, from where do I input in the load? This look confusing to me. Cause all I see if the feedback from the resistor back to the transistor. Do I just input the load from 12V source ? \$\endgroup\$ Commented Apr 12 at 3:26
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Look up a Howland Current-Pump circuit.

It uses an op amp to generate a bipolar current into an arbitrary grounded load.

What maximum voltage does this pulse need to be?

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