Transistor roles, characteristics and states
1. What is a transistor? What's the role?
Transistors are also called semiconductor diodes, which can be said to be the most important devices in electronic circuits. Its main function is the current amplification and switching, oscillation. The transistor is made of two PN junctions made of semiconductor material. Its three electrodes are connected to the three zones inside the tube ( emission region, base area and collector area ). The transistor has two types of NPN and PNP type.
The internal structure and graphical symbols of the PNP
The PNP type transistors consists of three semiconductors and consists of two PN junctions, namely, a collector junction and a emitter junction, and a total of three electrodes, the collector, the base and the emitter. The working current in the transistor has the collector current Ic, the base current IB, the emitter current Ie; Ic and IB from the emitter stream. The direction of the emitter arrow in the circuit symbol indicates the flow direction of the current. Ie=IB+Ic, because IB is small (negligible), then Ic≈Ie.
The internal structure and graphical symbols of the NPN type transistors.
The NPN type transistorswhich are different from those of PNP transistors.
The location of P type.N semiconductor is different, and the other is basically the same. The direction of the current is out of the emitter, the base current and the collector current are all inflow from the transistor, which can be seen from the direction of the emitter arrow in the symbol of the NPN type transistor circuit.
2.What are the characteristics of the transistors?
(1) the principle of current amplification the bias requirement. The transistor needs normal working conditions for the reverse bias of a collector junction, a voltage value of a few volts to a few hundred volts, a positive emission junction, a silicon transistor of 0.6~0.7V, a germanium transistor of 0.2~0.3V., or a NPN type transistor for E< B (silicon tube: 0.6~0.7V, germanium tube: 0.2~0.3V)
A transistor is a device that converts the power current to the signal current of the transmission. The transistor converts the DC current of the power supply into a signal current flowing through the transistor collector. The PNP transistor works the same as the NPN type, but the current direction is opposite, that is the emitter current current F base and collector. The relationship between the pole current and voltage of transistors. It is known from the above amplification principle that the relation between the polar current is Ie=Ic+IB and the IB is negligible, then the Ip Ic is the same as the Ie polar voltage on the IB polar voltage, that is, UB and UE, while IB and Ic are the opposite, that is UB and Uc.
(2) in the application of the output characteristics of the transistor, if the working voltage is changed, it will form three working states, that is, the cut-off area, the conduction (enlargement) area and the saturation area. Transistors operate in different areas and have different characteristics.
(1) The cut-off state. That is to say, when the emission is zero offset (not reaching the initial voltage value) or reverse bias, the transistor will not turn on when the collector junction is biased. At this point, there is no Ib, Ic or Ie, that is, the transistor does not work, U is about ten V at this time.
(2)Enlarge state. That is, when the emitter junction is positive and the junction reverse condition is set, the transistors form Ib, Ic, and the Ic changes with the Ib. At this time, the Ue and Uc change with the Uh, and the U transistor works in the linear region.
(3) Saturation state. That is, the collector bias is positive, the positive bias of emitter is greater than 0.8V, when Ib increases again, Ib almost no longer increases.
This article is from Allicdata Electronics Limited.