Structure And Working Principle Of ​Bipolar Junction Transistor

      Bipolar Junction Transistor is a common semiconductor component composed of three layers semiconductor materials. It has two PN junctions, three pins, and three regions. The middle layer is called base region. You can use a multimeter to determine  type, pin, and material of the transistor. For example, the Ground voltage of the three pins of the transistor measured with a multimeter DC voltage file is U1 = 2V, U2 = 6V, U3 = 2.7V, from which it can be judged that the transistor type is NPN, and the three pins are in turn E, C, B.

      According to package, transistor can be divided into plastic package and metal package.

      According to the arrangement, transistors can be divided into NPN type and PNP type.

      Let's learn working principle of the transistor. The crystal transistor can amplify the small current into a large current. If the transistor is capable of current amplification, the external conditions that must be met are the forward bias of the transmitting junction and the reverse bias of the collector junction.

In the amplifier circuit, the triode usually works in the amplified state. When the transistor is working in an amplified state, the emitter junction is positively biased. The voltage of the silicon tube is about 0.7V, and the voltage of the germanium tube is about 0.3V. If transistor in the cut-off state, the emitter junction is reverse bias and collector junction reverse bias. If the DC potentials of the three electrodes of a transistor on a circuit board measured to ground are VE = 3V, VB = 3.7V, and VC = 3.3V, the tube works in the saturation region.