Crystal diode and transistor amplifier circuit 4

We know that without applying voltage across the P-N junction, the diffusion of electrons and holes is hindered by the P-N junction potential barrier voltage and cannot continue. It is also known that applying a forward voltage can lower the barrier voltage of the P-N junction barrier layer, allowing diffusion to continue; If a reverse voltage is applied, the potential barrier voltage will increase and diffusion will stop.diode

Now assume that a forward voltage is applied to the emitter junction of a transistor (with the P region connected to the positive electrode of the battery and the N region connected to the negative electrode), and a reverse voltage is applied to the collector junction (with the P region connected to the negative electrode of the battery and the N region connected to the positive electrode). At this point, the barrier of the emitter junction decreases, allowing diffusion to occur. As a result, electrons in the base region run towards the left emitter region, and the empty space in the emitter region runs towards the base region. If Ib represents the hole current injected from the emitter junction into the base region and Ic represents the electron current injected from the emitter junction into the emitter region, then the total current Ie flowing out of the emitter junction is equal to the sum of the two.diode

In practical transistors, in order to meet the needs, people try to make the base region less doped with impurities, so its electrons are much fewer than the holes in the emission region, and the electron current is much smaller than the hole current, so Ib can be ignored, and Ie=Ic.diode

In this way, it can be clearly seen that the function of the emitter is to emit holes towards the base region, just like the cathode of an electron tube is specifically designed to emit electrons.diode