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I would like to use a modified version of this circuit with the Vin gauge being 13 g and the Vout (load) being 14g in an AC circuit. Aside from changing the op amp,and R6 how can i make this suitable for an AC circuit?enter image description here

  • \$\begingroup\$ I'm baffled? What does "Vin gauge being 13 g" actually mean in real words? Anyone? \$\endgroup\$
    – Andy aka
    Apr 9, 2018 at 8:29
  • \$\begingroup\$ The way the LED is controlled is very strange and inefficient. The normal way of doing it is changing the resistance of a transistor, connected in series. In this circuit the transistor is connected in parallel to the LED. \$\endgroup\$ Jan 20, 2020 at 0:42

1 Answer 1


It is not possible to use this type of circuit to limit a 20A AC line current unless it can dissipate hundreds of watts and withstand thousands of volts. (3kV)

In order to define a solution, you have a duty to define the problem with measurements and expected over-current limits and time duration.

Start surge current limiting is sometimes done with NTC poly-resitors.

It is always easier to limit current by regulating the load.

  • \$\begingroup\$ Sorry for the lack of detail. My goal is to limit the amount of current coming from the 13 gauge wire go into a 14 gauge wire. \$\endgroup\$ Apr 9, 2018 at 15:36
  • \$\begingroup\$ I understood that already. but that is not something one normally does. You only choose a fuse, breaker or load to suit the wire. But we'll never know with your lack of details on the application , load, concerns etc. It seems illogical. \$\endgroup\$ Apr 9, 2018 at 21:51
  • \$\begingroup\$ By the way, a 14 AWG wire can take surges greater and RMS rating. and AWG13 has only 30% more resistance thus temp rise accordingly. (approx) 3 wire gauges smaller = 50% lower Ohms/m \$\endgroup\$ Apr 9, 2018 at 21:58

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