Top ten most commonly used electronic components (II)

Zener diode:

Zener diode (also known as Zener diode), this diode is a semiconductor device with high resistance until the critical reverse breakdown voltage. Zener diode is commonly used in the circuit "ZD" plus digital representation, such as: ZD5 Indicates the voltage regulator numbered 5.

The voltage regulation principle of the Zener diode: The characteristic of the Zener diode is that after the breakdown, the voltage at both ends remains basically unchanged. Thus, when the voltage regulator is connected to the circuit, if the voltage of each point in the circuit fluctuates due to fluctuations in the power supply voltage or other reasons, the voltage across the load will remain substantially unchanged.

Fault characteristics: The fault of the Zener diode is mainly manifested in open circuit, short circuit and unstable voltage regulation value. Among the three types of faults, the former fault shows a rise in the power supply voltage; the latter two faults show that the power supply voltage goes low to zero volts or the output is unstable. The types and voltage regulation values of commonly used Zener diodes are as follows: Model 1N4728 1N4729 1N4730 1N4732 1N4733 1N4734 1N4735 1N4744 1N4750 1N4751 1N4761 Regulated value 3.3V 3.6V 3.9V 4.7V 5.1V 5.6V 6.2V 15V 27V 30V 75V.

inductance:

When the coil passes current, a magnetic field induction is formed in the coil, which in turn generates an induced current to resist current flow through the coil. We refer to this interaction of current and coil as the electrical inductive reactance, which is the inductance, in units of "Henry" (H). Inductive components can also be made using this property.

The inductor is usually represented by "L" plus a number in the circuit. For example, L6 represents the inductor number 6. The inductor coil is made by winding the insulated wire around the insulated bobbin by a certain number of turns. DC can pass through the coil. The DC resistance is the resistance of the wire itself. The voltage drop is very small. When the AC signal passes through the coil, the self-induced electromotive force will be generated at both ends of the coil. The direction of the self-induced electromotive force is opposite to the applied voltage, which hinders the AC. Pass, so the characteristic of the inductor is DC resistance AC, the higher the frequency, the greater the coil impedance. The inductor can form an oscillating circuit with the capacitor in the circuit. Inductors generally have a straight-label method and a color-code method, and the color-code method is similar to a resistor. Such as: brown, black, gold, gold means 1uH (error 5%) of the inductance.

The basic unit of inductance is: Hen (H) conversion unit: 1H = 103mH = 106uH.

Varactor diode:

Varactor diodes (VaractorDiodes) are also known as "variable reactance diodes". It is a diode made by the dependence and principle of the PN junction capacitance (barrier capacitance) and its reverse bias voltage Vr.

The varactor diode is a special diode specially designed according to the principle that the junction capacitance of the internal "PN junction" of the ordinary diode changes with the applied reverse voltage. The varactor diode is mainly used in the high-frequency modulation circuit of the mobile phone or the landline in the cordless telephone, and the low-frequency signal is modulated onto the high-frequency signal and transmitted. In the working state, the varactor diode modulation voltage is generally applied to the negative electrode, so that the internal junction capacitance of the varactor changes with the modulation voltage. The varactor diode fails, mainly due to leakage or poor performance:

(1) When a leakage phenomenon occurs, the high-frequency modulation circuit will not operate or the modulation performance will deteriorate.

(2) When the variable capacitance performance deteriorates, the operation of the high-frequency modulation circuit is unstable, and the modulated high-frequency signal is transmitted to the other party and received by the other party to generate distortion. When one of the above conditions occurs, the same type of varactor should be replaced.

Crystal Transistor:

The crystal triode is one of the basic components of semiconductors and has a current amplification function, which is the core component of electronic circuits. The triode is fabricated on a semiconductor substrate with two closely spaced PN junctions. The two PN junctions divide the positive block semiconductor into three parts, the middle part is the base area, and the two sides are the emitter area and the collector area, and the arrangement is PNP. And NPN two.

The transistor is commonly represented by a "Q" plus a number in the circuit. For example, Q17 represents a transistor numbered 17.

Features: A crystal triode (referred to as a triode) is a special device that contains two PN junctions and has amplification capability. It is divided into two types: NPN type and PNP type. These two types of triodes can complement each other in terms of working characteristics. The so-called tube in the OTL circuit is paired with PNP type and NPN type. PNP type triodes commonly used in telephones are: A92, 9015 and other models; NPN type triodes are: A42, 9014, 9018, 9013, 9012 and other models.

The transistor is mainly used for amplifying in the amplifying circuit, and there are three connections in the common circuit. For the sake of comparison, the characteristics of the three connection circuits of the transistor are listed in the following table for your reference. Name common emitter circuit common collector circuit (emitter output) common base circuit input impedance (several hundred ohms to several thousand ohms) large (tens of thousands of ohms or more) small (several ohms to tens of ohms) output impedance Medium (several thousand ohms to tens of thousands of ohms) small (several ohms to tens of ohms) large (tens of thousands of ohms to several hundred thousand ohms) voltage amplification factor (less than 1 and close to 1) large current amplification factor ( Dozens) large (tens of) small (less than 1 and close to 1) large power amplification (about 30 to 40 decibels) small (about 10 decibels) (about 15 to 20 decibels) frequency characteristics high frequency difference good The multi-stage amplifier intermediate stage is used, the low-frequency amplifying input stage, the output stage or the high-frequency or wide-band circuit and the constant current source circuit for impedance matching.