Diode, (English: Diode), among electronic components, is a device with two electrodes that only allows current to flow in a single direction. Many uses are for its rectification function. The varicap diode (Varicap Diode) is used as an electronic adjustable capacitor. The current directionality of most diodes is usually called "Rectifying" function. The most common function of a diode is to only allow current to pass in a single direction (called forward bias) and block in the reverse direction (called reverse bias). Therefore, the diode can be thought of as an electronic check valve.
1. Positive characteristics
When the forward voltage applied across the diode (P is positive and N is negative) is very small (germanium tube is less than 0.1 volts, silicon tube is less than 0.5 volts), the tube does not conduct, in the "off" state, when the forward voltage exceeds After a certain value, the tube is turned on, the voltage increases slightly, and the current increases sharply (see curve I). Diodes of different materials have different starting voltages, the silicon tube is about 0.5-.7 volts, and the germanium tube is about 0.1-0.3.
2. Reverse characteristics
When the reverse voltage is applied to the two ends of the diode, the reverse current is very small. When the reverse voltage gradually increases, the reverse current remains basically unchanged. The current at this time is called the reverse saturation current (see curve II). Diodes of different materials have different reverse currents. Silicon tubes are about 1 microampere to tens of microamperes, while germanium tubes can be as high as hundreds of microamperes. In addition, the reverse current is greatly affected by temperature changes. The stability is worse than that of silicon tubes.
3. Breakdown characteristics
When the reverse voltage increases to a certain value, the reverse current increases sharply. This phenomenon is called reverse breakdown (see curve III). The reverse voltage at this time is called the reverse breakdown voltage. The reverse breakdown voltage values ​​of tubes made of different structures, processes and materials vary greatly, ranging from 1 volt to several hundred volts, or even as high as thousands of volts.
4. Frequency characteristics
Due to the existence of junction capacitance, when the frequency is high to a certain extent, the capacitive reactance is so small that the PN junction is short-circuited. The diode loses unidirectional conductivity and cannot work. The larger the PN junction area, the larger the junction capacitance, and the less able to work at high frequencies.
Operating characteristics of the diode area1. Positive working area.
At this time, the diode is forward conduction, and the conduction current is determined by the external current, and the maximum forward working current of the diode is not exceeded. The forward conduction voltage drop increases slowly with the current, but the range of change is not large.
2. Dead zone.
The diode is still in a forward-biased state. Since the forward-bias voltage is too small and less than the diode turn-on voltage, the diode cannot be turned on, so the forward current is 0 at this time.
3. Reverse working area.
At this time, the diode is in a reverse working state, and the reverse current is very small. Generally, the silicon tube is a few uA to tens of uA, and the diode is not conducting. Together with the forward working area, this working area reflects the unidirectional conductivity of the diode and can be used for rectification and other occasions.
4. Reverse breakdown zone.
At this time, the diode is also in a reverse working state, but the back pressure is relatively large. At this time, the reverse working current of the diode will increase rapidly, but the reverse working voltage remains basically unchanged. This feature can be used for Zener diodes.
Conductive properties of diodesThe most important characteristic of a diode is its unidirectional conductivity. In a circuit, current can only flow in from the anode of the diode and flow out of the cathode.
Positive characteristics
In an electronic circuit, connect the anode of the diode to the high potential end and the cathode to the low potential end, and the diode will be turned on. This connection method is called forward bias. It must be noted that when the forward voltage applied to both ends of the diode is very small, the diode still cannot be turned on, and the forward current flowing through the diode is very weak. Only when the forward voltage reaches a certain value (this value is called "threshold voltage", also known as "dead zone voltage", the germanium tube is about 0.1 volts, and the silicon tube is about 0.5 volts), the diode can really turn on. After turning on, the voltage across the diode remains basically unchanged (the germanium tube is about 0.3 volts, and the silicon tube is about 0.7 volts), which is called the "forward voltage drop" of the diode.
Reverse characteristics
In an electronic circuit, the anode of the diode is connected to the low-potential end, and the negative electrode is connected to the high-potential end. At this time, almost no current flows in the diode, and the diode is in an off state. This connection method is called reverse bias. When the diode is reverse-biased, there will still be a weak reverse current flowing through the diode, which is called leakage current. When the reverse voltage across the diode increases to a certain value, the reverse current will increase sharply, and the diode will lose its unidirectional conductivity. This state is called diode breakdown.
Phase Control Thyristor is the abbreviation of thyristor, also known as silicon controlled rectifier, formerly referred to as thyristor; thyristor is PNPN four-layer semiconductor structure, it has three poles: anode, cathode and control pole; thyristor has silicon rectifier The characteristics of the parts can work under high voltage and high current conditions, and their working processes can be controlled and widely used in electronic circuits such as controlled rectifiers, AC voltage regulators, contactless electronic switches, inverters, and inverters.
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