High-power LED multi-function package integration technology ------ diode
Among diodes and electronic components, a device with two electrodes allows current to flow only in a single direction, and many of them use the function of rectification. The varactor diode (Varicap Diode) is used as an electronically tunable capacitor. The current directionality of most diodes is often referred to as the "Rectifying" function. The most common function of a diode is to allow only current to pass in a single direction (called forward bias) and reverse in reverse (called reverse bias). Therefore, the diode can be thought of as an electronic version of the check valve.
An early vacuum electronic diode; it is an electronic device that conducts current in one direction. Inside the semiconductor diode, there is a PN junction and two lead terminals. The electronic device has a unidirectional current conductivity according to the direction of the applied voltage. In general, a crystal diode is a p-n junction interface formed by sintering a p-type semiconductor and an n-type semiconductor. A space charge layer is formed on both sides of the interface to form a self-built electric field. When the applied voltage is equal to zero, the diffusion current is equal to the drift current caused by the self-built electric field due to the difference in the concentration of the carriers on both sides of the p-n junction, and is in an electric equilibrium state, which is also a diode characteristic in a normal state.
Early diodes included "Cat's Whisker Crystals" and vacuum tubes (known as "Thermionic Valves" in the UK). Most of the most common diodes today use semiconductor materials such as silicon or germanium.
characteristic
Positive
When the forward voltage is applied, the forward voltage is small at the beginning of the forward characteristic, which is insufficient to overcome the blocking effect of the electric field in the PN junction. The forward current is almost zero. This segment is called the dead zone. This forward voltage that does not turn the diode on is called the deadband voltage. When the forward voltage is greater than the deadband voltage, the electric field in the PN junction is overcome, the diode is forward-conducting, and the current rises rapidly as the voltage increases. In the current range of normal use, the terminal voltage of the diode remains almost constant during turn-on. This voltage is called the forward voltage of the diode. When the forward voltage across the diode exceeds a certain value, the internal electric field is quickly weakened, the characteristic current increases rapidly, and the diode is conducting. It is called the threshold voltage or threshold voltage, the silicon tube is about 0.5V, and the fistula is about 0.1V. The forward voltage drop of the silicon diode is about 0.6~0.8V, and the forward voltage drop of the germanium diode is about 0.2~0.3V.
Reverse
When the applied reverse voltage does not exceed a certain range, the current through the diode is the reverse current formed by the minority carrier drift motion. Since the reverse current is small, the diode is in an off state. This reverse current is also called reverse saturation current or leakage current, and the reverse saturation current of the diode is greatly affected by temperature. Generally, the reverse current of a silicon tube is much smaller than that of a tantalum tube. The reverse saturation current of a small power silicon tube is on the order of nA, and the low power tube is on the order of μA. When the temperature rises, the semiconductor is excited by heat, the number of minority carriers increases, and the reverse saturation current also increases.
Breakdown
When the applied reverse voltage exceeds a certain value, the reverse current suddenly increases. This phenomenon is called electrical
breakdown. The threshold voltage that causes electrical breakdown is called the diode reverse breakdown voltage. The diode loses unidirectional conductivity during electrical breakdown. If the diode does not cause overheating due to electrical breakdown, the unidirectional conductivity may not be permanently destroyed. After the voltage is removed, the performance is still restored, otherwise the diode is damaged. Therefore, the reverse voltage applied to the diode should be prevented from being too high.
A diode is a two-terminal device with unidirectional conduction. It has an electronic diode and a crystal diode. Because the heat loss of the filament is lower than that of the crystal diode, the diode is rarely seen. It is more common and commonly used. It is a crystal diode. The unidirectional conduction characteristics of diodes, semiconductor diodes are used in almost all electronic circuits, and it plays an important role in many circuits. It is one of the earliest semiconductor devices to be born, and its application is also very extensive.
The tube voltage drop of the diode: the silicon diode (non-illuminated type) has a forward voltage drop of 0.7V, and the forward tube voltage drop of the xenon tube is 0.3V. The forward voltage drop of the LED will vary with different illumination colors. There are three main colors. The specific voltage drop reference values are as follows: the voltage drop of the red LED is 2.0--2.2V, the voltage drop of the yellow LED is 1.8-2.0V, and the voltage drop of the green LED is 3.0-3.2V. The rated current when emitting light is approximately 20 mA.