Diode operation principle (positive conduction, reverse non-conduction) 10kw~3000kw wind inverter for Wind Turbine/Wind Generator Wind Inverter,Hydro Inverter,Wind Grid Inverter,Wind Power Inverter Jinan Xinyuhua Energy Technology Co.,Ltd , https://www.xyhenergy.com
The crystal diode is a pn junction formed by a p-type semiconductor and an n-type semiconductor, and a space charge layer is formed on both sides of the interface, and a self-built electric constant is formed. When there is no applied voltage, the carrier concentration on both sides of the pn junction is present. The diffusion current caused by the difference is equal to the drift current caused by the self-built electric field and is in an electrical equilibrium state.
When the outside has a forward voltage bias, the mutual suppression of the external electric field and the self-built electric field causes the diffusion current of the carrier to increase to cause a forward current. (This is also the reason for conduction)
When the outside has a reverse voltage bias, the external electric field and the self-built electric field are further strengthened to form a reverse saturation current that is independent of the reverse bias voltage value within a certain reverse voltage range. (This is why it is not conductive)
The crystal diode is a pn junction formed by a p-type semiconductor and an n-type semiconductor, and a space charge layer is formed on both sides of the interface, and a self-built electric constant is formed. When there is no applied voltage, the carrier concentration on both sides of the pn junction is present. The diffusion current caused by the difference is equal to the drift current caused by the self-built electric field and is in an electrical equilibrium state.
When the outside has a forward voltage bias, the mutual suppression of the external electric field and the self-built electric field causes the diffusion current of the carrier to increase to cause a forward current.
When the outside has a reverse voltage bias, the external electric field and the self-built electric field are further strengthened to form a reverse saturation current I0 that is independent of the reverse bias voltage value within a certain reverse voltage range.
When the applied reverse voltage is high to a certain extent, the electric field strength in the space charge layer of the pn junction reaches a critical value to generate a multiplication process of carriers, generating a large number of electron hole pairs, and generating a large reverse breakdown current. It is called the breakdown phenomenon of the diode.
There are many types of diode types of diodes, which can be classified into germanium diodes (Ge tubes) and silicon diodes (Si tubes) depending on the semiconductor material used. According to its different uses, it can be divided into detection diodes, rectifier diodes, Zener diodes, switching diodes, etc. According to the die structure, it can be divided into point contact diodes, surface contact diodes and planar diodes. The point contact diode is pressed on the surface of a clean semiconductor wafer with a very thin wire, and a pulse current is passed so that one end of the contact wire is firmly sintered with the wafer to form a "PN junction". Due to the point contact, it is only allowed to pass a small current (not more than tens of milliamps), and is suitable for high frequency and small current circuits, such as radio detection.
The "PN junction" area of ​​the surface contact type diode is large, allowing a large current (a few amps to several tens of amps) to be used, mainly for converting the alternating current into a "rectifying" circuit of direct current.
The planar diode is a special type of silicon diode that not only passes large current, but also has stable and reliable performance. It is widely used in switching, pulse and high frequency circuits.
The most important characteristic of a diode's conductive diode is its unidirectional conductivity. In the circuit, current can only flow from the positive pole of the diode and the negative pole flows out. The forward and reverse characteristics of the diode are illustrated by simple experiments.
1. Forward characteristics In the electronic circuit, the positive pole of the diode is connected to the high potential end, the negative pole is connected to the low potential end, and the diode is turned on. This connection method is called forward bias. It must be stated that when the forward voltage applied across the diode is small, the diode is still not conducting, 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", the xenon tube is about 0.2V, and the silicon tube is about 0.6V), the diode can be turned on. The voltage across the diode remains essentially constant after conduction (the transistor is approximately 0.3V and the silicon tube is approximately 0.7V) and is referred to as the "forward voltage drop" of the diode.
2. Inverse characteristics In the electronic circuit, the positive pole of the diode is connected to the low potential end, and the negative pole is connected to the high potential end. At this time, almost no current flows through the diode. At this time, the diode is in the off state. This connection method is called Reverse bias. When the diode is reverse biased, there is still a weak reverse current flowing through the diode, called the 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 conduction characteristics. This state is called diode breakdown.
The main parameters of the diode are used to indicate the performance of the diode and the technical specifications of the applicable range, called the parameters of the diode. Different types of diodes have different characteristic parameters. For beginners, you must understand the following main parameters:
1. The rated forward working current refers to the maximum forward current value that the diode is allowed to pass during long-term continuous operation. When the current passes through the tube, the die heats up and the temperature rises. When the temperature exceeds the allowable limit (about 140 for the silicon tube and about 90 for the manifold), the die is overheated and damaged. Therefore, the diode should not exceed the rated forward operating current of the diode. For example, the commonly used IN4001-4007 type germanium diodes have a rated forward operating current of 1A.
2. When the highest reverse working voltage is applied to the reverse voltage across the diode to a certain value, the tube will be broken down and the unidirectional conduction capability will be lost. In order to ensure safe use, the highest reverse operating voltage value is specified. For example, the IN4001 diode has a reverse withstand voltage of 50V and the IN4007 has a reverse withstand voltage of 1000V.
3. Reverse current Reverse current refers to the reverse current flowing through the diode under the action of the specified temperature and the highest reverse voltage. The smaller the reverse current, the better the unidirectional conductivity of the tube. It is worth noting that the reverse current has a close relationship with temperature. For every 10 rises in temperature, the reverse current doubles. For example, the 2AP1 type germanium diode, if the reverse current is 250uA at 25 o'clock, the temperature rises to 35, the reverse current will rise to 500uA, and so on. At 75 o'clock, its reverse current has reached 8mA, not only lost. Unidirectional conductive properties can also cause the tube to overheat and be damaged. Another example is the 2CP10 type silicon diode. The reverse current is only 5uA at 25 o'clock, and the reverse current is only 160uA when the temperature rises to 75. Therefore, silicon diodes have better stability at high temperatures than germanium diodes.
Test diodes for good or bad beginners in amateur conditions can use a multimeter to test the performance of the diode. Before the test, first turn the multimeter's switch to the RX1K position of the ohmic file (be careful not to use the RX1 file to avoid excessive current burnout of the diode), and then short-circuit the red and black test leads to perform ohm-zero adjustment.
1. Forward characteristic test Put the black meter of the multimeter (positive in the table) to touch the positive pole of the diode, and the red test lead (negative electrode in the meter) touches the negative pole of the diode. If the hands do not swing to the value of 0 but stop in the middle of the dial, the resistance at this time is the forward resistance of the diode. Generally, the smaller the forward resistance, the better. If the forward resistance is 0, the die short circuit is damaged. If the forward resistance is close to infinity, the die is broken. Both short-circuited and open-circuited tubes cannot be used.
2. The reverse characteristic test puts the red test pen of the Wanhe table on the positive pole of the diode, and the black test pen touches the negative pole of the diode. If the needle refers to the infinity value or close to the infinity value, the tube is qualified.
Diode application
1. The rectifier diode uses the unidirectional conductivity of the diode to convert the alternating current alternating in direction into a pulsating direct current in a single direction.
2. The switching element diode has a small resistance under the action of the forward voltage, and is in a conducting state, which is equivalent to a switch that is turned on; under the action of the reverse voltage, the resistance is large and is in an off state, like a disconnected switch. Various switching logic circuits can be used to form various logic circuits.
3. After the diode of the limiting element is forwarded, its forward voltage drop remains basically the same (0.7V for the silicon tube and 0.3V for the manifold). Using this feature, as a limiting component in the circuit, the signal amplitude can be limited to a certain range.
4. The relay diode acts as a relay in the inductance of the switching power supply and in the inductive load such as the relay.
5. The detector diode acts as a detector in the radio.
6. The varactor is used in the tuner of the TV set.