Analysis of the Structure and Type of Transistor

Transistor, is one of the basic semiconductor components, with current amplification, is the core component of the electronic circuit. Transistor is the production of two semiconductor substrates in a very close PN junction, the two PN junction to the block semiconductor is divided into three parts, the middle part is the base area, both sides of the emitter and collector area, the arrangement of PNP And NPN two kinds, as shown in the figure leads from the three areas of the corresponding electrode, respectively, base b emitter e and collector c.

The PN junction between the emitter and the base is called the emitter junction, and the PN junction between the collector and base regions is called the collector. The base area is very thin, while the emitter area is thick and the impurity concentration is high. The emitter of the PNP type transistor emits holes. The moving direction is the same as the current direction, so the emitter arrow is inward. The emitter of NPN transistor emits "Is a free electron, the direction of its movement and current direction, so the emitter arrow outward. Emitter arrow outward. The emitter arrow point is also the conduction direction of the PN junction at forward voltage. Silicon transistor and germanium transistor have PNP type and NPN type two types.

Transistor package and pin identification

Commonly used transistor package in two categories: metal package and plastic package, the pin arrangement has a certain pattern, as shown in the figure for low-power metal-clad transistor, placed in the position shown in the bottom view, so that the three pins constitute the isosceles Triangle vertices, from left to right, followed by ebc; for small and medium power plastic figure according to the map to their own plane, the three pins down, then from

From left to right are ebc.

At present, there are many types of crystal transistors of various types in China. The arrangement of the pins varies. In use, the transistors with indefinite pin-outs must be measured to determine the correct position of each pin, or to find the transistor manual, Transistor characteristics and the corresponding technical parameters and information.

Crystal transistor current amplification

Transistor transistor has a current amplification, the essence of the transistor can base current small amount of change to control the collector current larger amount of change. This is the most basic transistor and the most important features. We will ΔIc / ΔIb ratio called the transistor current magnification, with the symbol "β" said. Current magnification for a certain transistor is a constant value, but with the transistor base current work changes will be some change.

Transistor three working conditions

Cut-off state: when the voltage applied to the emitter of the transistor is less than the PN junction voltage, the base current is zero, the collector current and emitter current are both zero, and the transistor then loses current amplification. The collector and emitter Equivalent to the switch between the open state, we call the transistor in the off state.

Enlarged state: When the voltage applied to the emitter of a triode is greater than the turn-on voltage of the PN junction and is at an appropriate value, the emitter of the transistor is forward biased and the collector junction is reverse biased. At this time, the base current Collector current plays a controlling role, the transistor has a current amplification, the current amplification factor β = ΔIc / ΔIb, then the transistor amplification.

Saturated turn-on state: when the voltage applied to the transistor emitter junction is greater than the PN junction turn-on voltage, and when the base current increases to a certain extent, the collector current no longer increases with the base current increases, But rather in the vicinity of a certain value is not very changed, then the transistor loss of current amplification, collector and emitter voltage is very small, collector and emitter equivalent switch between the conduction state. This state of the transistor we call saturated conduction state.

According to the work of the transistor when the potential of each electrode, you can determine the working status of the transistor, therefore, electronic maintenance personnel in the maintenance process, often need to use multimeter to measure the voltage of each leg of the transistor to distinguish the work of the transistor and the working conditions.

Use multimeter detection transistor

Transistor base discriminate: According to the triode structure diagram, we know that the base of the transistor is the common pole of the two PN junction transistor, so in the identification of the base of the transistor, as long as the two poles to find out the common pole, That is the base of the transistor. The specific method is transferred to the multimeter to block R × 1k block, first with a red pen on a pin of the transistor, with a black pen to touch the other two pins of the transistor, if the two all-pass, the red Pins put the pin is the base of the transistor. If you do not find a while, then the red pen to another transistor triode, and then measured twice; if not found, the red pen and then look for another test twice. If you have not found, then use a black pen on the transistor on a pin, with a red pen to test twice to see if all-pass, if not successful again. This measurement up to 12 times, you can always find the base.

Transistor type of discrimination: Transistor only two types, namely PNP and NPN type. As long as you know when the base is P-type material or N-type material can be. When using a multimeter R × 1k file, the black pen on behalf of the positive power supply, if the black pen connected to the base when the conduction, then the base of the transistor P-type material, the transistor is NPN type. If the red pen then connected to the base, then the transistor base is N-type material, the transistor is PNP type.