Just by clicking on the resistor, I got a display of the plot of current passing through it, marked with I(R3). In my opinion it must be in phase with the voltage across the resistor, but on the screenshot it seems to be different, could anyone help me to understand it?

enter image description here


Turn the resistor around. :)

Electric current has a direction, it is not a scalar property of a resistor. And there is no a priori given "positive" direction neither. Spice simply assumes that the current flowing from one resistor terminal to another has positive sign and opposite direction is displayed as negative. Because terminal numbering is "hidden" and the visual symbol has both terminals indistinguishable, it can be a bit perplexing.

LTspice will hint you what is the positive current direction by changing the cursor shape when you hover it over the component in "probe" mode.

  • \$\begingroup\$ you can see the voltage at node 3 and 4, and probe cursor direction for R3 is showing towards <----- (left side). we have the voltage difference across the resistor, then it is obvious that what should be the direction of current but here... \$\endgroup\$
    – Aku Jack
    Sep 15 '19 at 20:40
  • \$\begingroup\$ Cursor shows you what will be interpreted as a positive current, that is current flowing from the right to left will be displayed as a positive in your case. That is exactly what you got (when current in the circuit is flowing from right to the left, so it is displayed as negative value). Once again, current is not a scalar property of a resistor, therefore there is no "obvious" positive value. You need to multiply the positive direction vector (as shown by the cursor) by plotted value to get actual direction. If you do not like "inverted" values, simply turn the resistor around. \$\endgroup\$
    – Martin
    Sep 15 '19 at 20:45
  • \$\begingroup\$ agreed, but turning the resistor around not changing anything. I guess its a default setting like this, thanks bro, Can I have an upvote for the question, for happily accepting the answer \$\endgroup\$
    – Aku Jack
    Sep 15 '19 at 21:05
  • \$\begingroup\$ Rotating (or mirroring) the resistor should invert the reported sign. Are you sure you have rerun simulation after the change? \$\endgroup\$
    – Martin
    Sep 15 '19 at 21:09
  • \$\begingroup\$ yep ! you can rotate it by ctrl + R, which won't change anything, even the appearance \$\endgroup\$
    – Aku Jack
    Sep 15 '19 at 21:15

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