# Transistor understanding

#### Bogdan_Ionut

Joined Oct 5, 2021
9
As far as I understand the regular NPN Transistor works like this:
If Base is connected to power, collector sends electricity to emitter, if base is unplugged, collector doesn't send electricity to emitter.
Do you know a model of NPN transistor with a collector that works with AC electricity(max 100 V) and a base that needs AC to activate the transistor?

#### Audioguru again

Joined Oct 21, 2019
3,846
A transistor works with DC, not AC.
A triac is a device used in an AC light dimmer that can pass or not pass AC electricity depending on the signal at its gate terminal.

#### crutschow

Joined Mar 14, 2008
28,201
What are you trying to control?

#### LvW

Joined Jun 13, 2013
1,337
As far as I understand the regular NPN Transistor works like this:
If Base is connected to power, collector sends electricity to emitter, if base is unplugged, collector doesn't send electricity to emitter.
No, your description is incorrect. Do you know how a pn-diode works? The npn transistor works quite similar.
In short:
* A base-emitter voltage of app. (0.6...0.7) volts "opens" the transistor, which means: Electrons are released from the n-doped emitter region and travel to the p-doped base region. That is the emitter current Ie.
* The base region is extremly thin and most of the electrons cross this region (drift effects and accelaration caused by the positive collector voltage). They flow through the collector terminal and form the collector current Ic (slightly smaller than Ie).
* However, a small part does not reach the collector, but flows through the base terminal (base current Ib).
* Hence, we have: Ie=Ic+Ib.
* The absolute magnitude of these three currents is determined by the magnitude of the B-E voltage Vbe, because the bipolar transistor is a voltage-controlled device (see the well-known Shockley equations, known from the diode pn junction).