Intrinsic semiconductor (weak conductor)

Conductivity ~ carrier concentration ~ temperature

Impurity semiconductor: intrinsic semiconductor trace element → conductivity changes

Diffusion motion = drift motion → dynamic equilibrium = PN junction formation

The depletion layer becomes narrower, the movement intensifies, the external power supply generates diffusion current, and the PN junction is in a conductive state.

The depletion layer becomes wider, preventing diffusion movement, aggravating drift movement, small current amount, and PN junction cutoff

Small junction area, small junction capacitance, small forward current, suitable for high-frequency and low-power operation, and also used for switching components in digital circuits

Large junction area, large junction capacitance, and large forward current, suitable for low-frequency rectifier circuits

Used in integrated circuit manufacturing process. PN junctions can be large or small and are used in high-frequency rectification and switching circuits.

The applied voltage is greater than the dead zone voltage, and the diode

Only when the applied voltage is greater than the reverse breakdown voltage can the diode be turned on. The tube is broken down and loses one-way conductivity.

The maximum forward average current allowed to flow through the diode when the diode is used for a long time.

It is the reverse peak voltage given to ensure that the diode is not broken down. It is generally one-half or two-thirds of the reverse breakdown voltage UnR of the diode. After the diode breaks down, it conducts electricity in one direction, its properties are destroyed, and it may even overheat and burn out.

Refers to the reverse current value when the reverse operating peak voltage is applied to the diode. The smaller the reverse current, the better the one-way conductive performance of the tube. Temperature has a great influence on the maximum reverse current, so you should pay attention when using it.

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Voltampere characteristics

The main parameters





The emitter junction is forward biased and the collector junction is reverse biased.



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Judgment status

DC current amplification factor

AC current amplification factor

Including the collector-base reverse cut-off current IcBo and the collector-emitter reverse cut-off current IcEo, where Icpo=(1 B)IcBO, both are greatly affected by temperature, and the smaller the value, the better.

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(1) The role of transistor T

(2) The role of collector power supply Ucc

(3) The role of collector resistance Rc

(4)The role of base resistor Rp



The working state of the amplifier circuit when there is no signal input (u;=0).

Determine the quiescent value of the amplifier circuit. A static operating point Q: Ip, Ic UcE

Estimation method

Graphical method

The DC component of the voltage and current of each pole.

The DC path of the amplifier circuit.

(1) Prevent the amplified signal of the amplifier circuit from being distorted;

(2) Make the amplifier circuit work in a better working state. Static is the basis of dynamic.

1. Calculation of voltage amplification factor

2. Calculation of input resistance of amplifier circuit

3. Calculation of the output resistance of the amplifier circuit

The principle of Q point, in a fixed bias amplifier circuit, when the temperature rises, UBE↓, β↑, IcBo↑.

Parameter selection

The process of Q point stabilization



Voltage amplification factor

Input resistance

Output resistance

Features of common collector amplifier circuit (emitter output device):

Connect the output terminal of the previous stage directly to the input terminal of the subsequent stage. It can be used to amplify slowly changing signals or signals with direct changes.

(1) The static working points of the front and rear stages interact with each other

(2) Zero point drift

Directly affects the accuracy and resolution of input signal measurement. Au

In severe cases, the effective signal voltage may be submerged, making it impossible to distinguish whether it is the effective signal voltage or the drift voltage. Au

Generally, the output drift voltage is converted to the equivalent drift voltage of the input terminal as an indicator to measure the zero point drift. Au

Only when the equivalent drift voltage at the input end is much smaller than the input signal, the amplified useful signal can be well distinguished. .



(1) The common mode signals u1=up2 are equal in size and polarity.

(2) Differential mode signals un=-up are equal in size and opposite in polarity



(1) Able to output as much power as possible without distortion.

(2) Due to the large power, it is required to improve efficiency.

The complementary symmetrical circuit is the basic form of the output stage of the integrated power amplifier circuit. When it is coupled to the load through a large-capacity capacitor, it is called an Output Transformerless circuit, or OTL circuit for short, because it eliminates the need for a transformer. If the complementary symmetrical circuit is directly connected to the load and the output capacitor is omitted, it becomes an output capacitorless circuit, or OCL circuit for short. The OTL circuit is powered by a single power supply, and the OCL circuit is powered by dual power supplies.

At present, integrated power amplifier circuits have been widely used, and their internal circuits are generally OTL or OCL circuits. In addition to the advantages of discrete component OTL or OCL circuits, integrated power amplifiers also have the advantages of small size, stable and reliable operation, and ease of use. There are many types of low-frequency integrated amplifiers. Let’s take the LM386 as an example for a brief introduction. LM386 is a low-voltage general-purpose low-frequency integrated amplifier. This circuit has low power consumption, wide allowable power supply voltage range, wide pass-band bandwidth, and few external components. It is widely used in radio recorders, walkie-talkies, TV audio and other systems.