Electrical books say that we can use transistor to amplifying current but when I simulate a circuit in proteus input current, it is smaller than emitter current but why?

This is a common collector and we expect that the current to be amplified at the emitter point.

I at p1 point is greater than I at p2

  • \$\begingroup\$ @horta and em fields and peter bennett ok! so what is the benefit of transistor? i connect directly motor to power supply and dont need transistor. \$\endgroup\$ – Ehsan F Nov 22 '16 at 18:35
  • \$\begingroup\$ You can't amplify the current of the battery/power supply with the transistor, the transistor is used so that MCUs and other devices can deal with higher currents than they would be able to. \$\endgroup\$ – Wesley Lee Nov 22 '16 at 18:44
  • \$\begingroup\$ Transistor is not a source of any current or voltage (transistor is not a battery). What is happening is that the base current is controlling the amount of current that transistor can pass from supplies voltage to the load. Just like a water tap. \$\endgroup\$ – G36 Nov 22 '16 at 19:12
  • \$\begingroup\$ @G36 can you say a simple example or compare with another devices? thanks alot \$\endgroup\$ – Ehsan F Nov 22 '16 at 19:19
  • \$\begingroup\$ en.wikipedia.org/wiki/Amplifier \$\endgroup\$ – Bruce Abbott Nov 22 '16 at 19:20

You appear to be comparing the current supplied by the battery to the current from the transistor's emitter. This is incorrect.

Some of the current from the battery will flow through the potentiometer, so the emitter current must be less than the battery current.

The gain of a transistor in this circuit is the ratio of the emitter current to the base current.

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You are getting current amplification. Ib to Ie is getting amplified: 0.15mA -> 6.5mA. That's a current gain of ~43X.

The output of the battery has to account for all of this current so that's why it's greater than Ie. A little bit of current from the battery flows through the 10K resistor which is why the battery current shows more current than any other point.

To be clear, a transistor amplifies current between its nodes. It cannot make a battery source more current than the battery will output on its own. The exception to this is if you have a boost converter or a circuit that isn't just aimed at regulating current.

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