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I have pulse with both negative and positive sides, say -4v to +4v. I want to limit the current for both sides to 1mA. I know how to limit the current of a 0 to 5v pulse using two transistors but I am not sure how to apply it to a -4- to 4v pulse. Any suggestion?

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  • \$\begingroup\$ Resistance limits current according to ohms law. \$\endgroup\$ – Andy aka Aug 9 '15 at 11:52
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Generic answer for the question- if your unipolar regulator circuit blocks reverse voltage, then put two complementary circuits in parallel. If it conducts in reverse then put two complementary circuits in series or two unipolar in series back-to-back.

For example, if you were to use current regulator diodes (which are basically a JFET and resistor) they conduct in the reverse direction so you could do this:

enter image description here

CLDs are fairly rare and relatively expensive these days, so it probably wouldn't be your preferred solution- just an example since you have a circuit in mind.

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    \$\begingroup\$ another option in a similar vein is put a unidirectional current limit circuit inside a bridge rectifier, \$\endgroup\$ – Jasen Aug 9 '15 at 7:20
  • \$\begingroup\$ @Jasen Good one. Schottky diodes could be used to reduce the drop. One advantage of Jasen's approach is that it will be very symmetrical. \$\endgroup\$ – Spehro Pefhany Aug 9 '15 at 7:21
  • \$\begingroup\$ Thanks guys. I think this bridge thing can work for me. I am going to try it. \$\endgroup\$ – Reza Aug 9 '15 at 8:43

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