So I built this circuit and I am trying to measure the emitter current, and the LTSpice simulation is giving me negative value reading... any idea why? enter image description here

  • \$\begingroup\$ Negative currents are out of a pin. Positive currents are into a pin. The sum of all the currents into and out of the BJT should be zero. (The BJT isn't a Coulomb bucket.) \$\endgroup\$ – jonk Dec 7 '19 at 21:26
  • \$\begingroup\$ @Jonk why not 'answer' the question? \$\endgroup\$ – Huisman Dec 7 '19 at 21:39
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    \$\begingroup\$ @Huisman Because I'd feel a need to provide more detail and explanation. I don't have the time for that. Sure, a lot of people here do write very short answers, collect a bunch of points for it, and feel fine about it. I don't. I don't think you can find a single short answer here without my taking time for context -- well, there is one but I'm not telling on myself! I may be wrong about my answers. I obviously make mistakes and have wrong ideas. But I do provide the context from which I'm coming. I just don't have the time right now to provide an answer with my name on it. Maybe later? \$\endgroup\$ – jonk Dec 7 '19 at 21:44
  • \$\begingroup\$ @jonk I understand and very much like your style not to write cheap answers! \$\endgroup\$ – Huisman Dec 7 '19 at 21:53
  • \$\begingroup\$ Always make sure to look a the mouse cursor direction arrow when you click somewhere to display a current. In LTSpice, even passive components like resistors will have a pre-defined direction for what a positive current represents and if you put the resistor into the circuit the wrong way around, the graph will reflect this even though it will have no bearing on the function of the circuit. \$\endgroup\$ – DKNguyen Dec 7 '19 at 21:58

This is what I found in the Electronic Devices book by Stephen Fleeman.

During the development of the V-I curves (and on manufacturers' data sheets), it is customary to apply the transistor convention. The transistor convention has been defined in Fig. 4-10(a).

Currents that flow into the transistor are called positive. Conversely, currents that flow out of the transistor are called negative. If the actual conventional current directions agree with the transistor convention, they are called positive. If not, they are called negative. enter image description here

  • \$\begingroup\$ Good catch. Thanks! \$\endgroup\$ – jonk Dec 8 '19 at 15:02
  • \$\begingroup\$ Thanks for explanation! \$\endgroup\$ – tsotniuspious Dec 8 '19 at 20:30

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