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Structure and classification of transistors
Their common feature is three electrodes, which is the origin of "transistor". Generally speaking, transistors are composed of three layers: P-type semiconductor and N-type semiconductor, which are divided into two types according to the hierarchical structure order: NPN type and PNP type.
These three regions are the above-mentioned three-layer structure, the base region of a relatively thin intermediate layer and two other transistors of N type or P type, in which the emitter region with relatively small size and majority carriers, the layer with relatively high sub-concentration and the other layer are compared with the collector region. The characteristic of this internal structure is that the transistor can play a greater role under internal conditions.
The three electrodes of each lead in the three regions are respectively used as the emitter (e) and the collector (c) in the base (b).
As shown in Figure B, the three-layer structure can form two PN junctions, which are called emitter junction and collector junction respectively. The direction of the arrow in the transistor symbol indicates the direction of the emitter junction.
There are two unidirectional PN junctions in the internal structure of the transistor, which can of course be used as a switching element, but at the same time, the transistor is also an amplification element, which promotes the leap-forward development of electronic technology.
Current amplification of transistor 2
The DC voltage source Vcc should be greater than Vbb, so that the circuit can meet the external conditions of amplification: forward bias of emitter junction and reverse bias of collector. By changing the adjustable resistor Rb, the base current IB, collector current Ic and emitter current IE will all change, and the following conclusions can be drawn from the measurement results:
(1)IE = IB+IC (according to Kirchhoff current theorem)
(2)IC≈IB×？ (The so-called current amplification factor is a representation of current amplification in a transistor.)
(3)△ integrated circuit ≈△IB×?
As shown above, the transistor is a current amplifier of analog devices.
3 triode amplification principle
/& gt； The following NPN transistors, such as the movement law of internal carriers, current amplification.
Principle,
1, emitter, base diffused electrons: the push-out junction is forward biased, and the majority carriers (free electrons) in the continuous emitter diffuse to the base, which are continuously supplemented by electrons from the power supply, forming emitter current IE.
2. Electron diffusion in the base region and composite materials: Because the concentration of majority carriers (holes) in the thin base region is very low, a relatively small base current IB is formed in the base region, and only a small part of electrons in the base region can diffuse from the emitter and recombine with the holes, while most of the remaining electrons can diffuse to the edge of the collector junction.
3. Electrons collected in the collector region diffuse from the emitter region: the collector junction is reversely biased, which can diffuse from the emitter region to the base region and reach the edge of the collector and be pulled into the collector region, thus forming a larger collector current IC.
Input and output characteristics of four transistors
The characteristic of input transistor refers to the relationship curve between base current IB and base-emitter voltage UBE, that is, constant collector-emitter voltage UCE.
For the silicon tube, when the UCE exceeds 1V and the collector junction has reached enough reverse bias, the electrons diffused from the emitter region to the collector region pull most of the base region. Then increase, as long as UCE UBE remains unchanged (the electrons emitted by the emitter are in a certain number of base regions), IB remains basically unchanged. That is to say, when the UCE exceeds 1V after the input characteristic curve, it basically coincides.
As can be seen from the figure, as well as the volt-ampere characteristics of the diode, there are some dead zones in the transistor characteristics of the input transistor. Only when UBE is greater than the voltage of the dead zone, the base current IB. Generally, the voltage of silicon tube is about 0.5V, and that of germanium tube is about 0.1v.. Under normal working conditions, NPN silicon tube UBE 0.6? The emitter voltage is 0.7V, and the emitter-base junction UBE voltage of PNP germanium tube is -0.2? -0.3V .
Output characteristics of transistor, collector current IC collector-emitter voltage UCE curve when base current IB is constant. According to IB, it can come from different curves, so a set of transistor output characteristic curves. Usually can be divided into three aspects:
Amplification area: the output characteristic curve of the horizontal part near the amplification area of the output characteristic curve. In the amplification area, IC = IB? Therefore, it is approximately equal to the current amplification coefficient at different IB, and the amplified region is also called linear region. When the three transistors work in the forward bias of the emitter junction in the amplification region, silicon UBE >: 0, UBC <: 0。
2. Cut-off area: The area under the curve with IB = 0 is called the cut-off area. In fact, NPN silicon tube, when ube
3. Saturation region: the steep part of the output characteristic curve is saturated region, and the change of IB has little effect. Is it in the amplification area of IC? "No longer applies to the saturated zone. In the saturated region, UCE
Measurement judgment transistor formula
Triode tube and pin distinguish the basic skills of beginners in electronic technology and help readers master measurement quickly.
For the laws of both contracting parties, the author summarizes four formulas: "hanging upside down, looking for a base;" PN junction tube; Forward arrow deflection; Uncertainty,
Move your mouth. "Let's explain it by stepping on it.
3 hang upside down and find the base.
As we all know, a transistor is a semiconductor device, which includes two PN junctions. Can be divided according to the following factors
For the connection of two PN junctions of NPN and PNP transistors with different conductivity types, figure 1 is the circuit symbol and equivalent circuit.
To test the transistor, use a multimeter to block the ohm gear, and block R× 100 or R× 1K ... Figure 2 Digital multimeter.
Ohm equivalent circuit device. As can be seen from the picture, the red stylus is connected to the negative electrode of the battery watch and the black stylus.
The billiard table is connected to the positive pole of the power supply.
Suppose we don't know, and we can't tell exactly what type of transistor NPN or PNP the pin electrode is measuring. test
The first step is to determine which pin is the basis. At this time, we take any two electrodes (such as two electrodes 1, 2).
The two probes of the ammeter measure the positive and negative resistances of the multimeter, observe the deflection angles of the probes, and then take two 1 3 electrodes.
2, 3 two electrodes, respectively, inverted to measure their positive and negative resistance, observe the deflection angle of the watch hand.
Three times of reverse measurement must have the results of nearly two measurements: (1) When the deflection of the reverse measuring needle is large, the deflection is small; The remaining time will be
Of course, on the contrary, the deviation angle of the front and back hands is small, and this unexpected bird's foot is the basis we are looking for (see
Figure 1, Figure 2 is easy to understand).
2. In a PN junction, a given tube
After finding the base of the transistor, we can determine the direction and base of the PN junction between the two electrodes.
Conductivity type (Figure 1). To the base where the black pen of the multimeter contacts, the red pen contacts the electrode of any other two electrodes.
If the deflection angle of the instrument pointer is measured, the measuring transistor is an NPN tube; The head pointer is deflected by a small angle, i.e.
The measuring tube is PNP type.
Forward arrow, deflection
Find the base B, the other two electrodes, which are the collector C and the emitter E? when we
The measurable current of ICEO penetration determines the collector C and emitter E.
(1) For the NPN transistor, the tunnel current measuring circuit is shown in Figure 3. According to this principle, use a multimeter.
Turn the black and red pens upside down to measure the forward and reverse resistance of RCE, and record the resistance between the two poles.
The two measurements of the deflection angle of the multimeter pointer are very small, but careful observation shows that when the deflection angle is slightly larger, the direction of current flow must be: black stylus → C → B.
Very, very, very →→→ E red pen, the arrow in the direction of current flow just coincides with the transistor symbol ("forward arrow"), so in this case,
The black contact pin is connected to the collector C and the red contact pin is connected to the emitter E. ..
(2) For PNP transistor, the parameters are similar to NPN type, and the current must be: black needle →E→B pole.
→c pole → red stylus, the direction of current and arrow symbol are consistent with the direction of transistor, so
The black pen is connected to the emitter E, and the red pen collector must be connected to C (see figure 1, as shown in figure 3).
4 Uncertain and dynamic ports
In the process of large deflection measurement along the arrow, it is difficult because the deflection of the pointer after the first two measurements is too small.
To distinguish, we must "talk". The specific method is: measure the large deflection along the arrow twice, twice.
Pinch the joint of two needles by hand, and pinch (or pinch with tongue) the base electrode B. The discrimination method still in use can be separated along the arrow.
The deflection of large "collector c and emitter e", the role played by the body, DC bias resistance, magnetic head.
Make the effect more obvious.