Among the electronic component family, there is a component that only allows current to flow in a single direction, called a diode, and English is "Diode", is the cornerstone of the modern electronics industry.
Early diode
Early diodes contained "Cat's Whisker Crystals and vacuum tubes).
In 1904, the British physicist Fleming invented the world's first electronic diode - vacuum electronic diode in the world according to the "Edison effect". It relies on cathode thermal emission electrons to the anode to achieve conduction.
The power supply positive and negative poles cannot be electrically conductive, which is an electronic device capable of one-way conductive current. The early electronic diode has a large volume, preheating, power consumption, easy to break, etc., the invention has prompted the invention of the crystal diode.
Crystal diode
Semiconductor diode is also known. In 1947, the Americans invented. There is a pn junction and two lead terminals inside the semiconductor diode.
Such an electronic device has a directional conductivity of a single-way current in accordance with the direction of the external voltage. Today, most common diodes are mostly using semiconductor materials such as silicon or germanium.
Crystal diode structure
The core of the crystal diode is PN knot, and the PN knot first to understand three concepts.
The intrinsic semiconductor: refers to a semiconductor that does not contain any doped elements, such as a pure silicon wafer or a pure germanium wafer.
P-type semiconductor: doped a semiconductor having a lower electric price impurity containing holes, such as a semiconductor of Al (3+) in Si (4+) in the semiconductor.
N-type semiconductor: doped a semiconductor having a lower electric price impurity containing holes, such as semiconductors incorporating phosphorus P (5+) in silicon Si (4+) in the semiconductor.
When in contact with the p-type semiconductor and the n-type semiconductor, a unique PN junction interface is generated, and a spatial charge layer is formed on both sides of the interface to form a self-construction electric field.
When the external voltage is equal to zero, since the concentration difference between the two carriers of the PN junction causes the diffusion current and the drift current caused by the self-built electric field, it is in an electrical equilibrium state, which is also a PN junction under normal state.
The pn junction is the core structure, and the lead or pin forms a one-way electrically conductive diode.
When the external voltage direction is directed by the p pole to the N pole, turned on.
Crystal diode classification
The crystal diode can be classified in different parts of the material and the PN junction structure.
01 point contact diode
The point contact diode is formed by pressing a metal needle on a single wafer of the germanium or silicon material, and is formed by a current method.
Its PN junction is small and suitable for high frequency circuits. Because the structure is simple, the price is cheap. For small signals, rectification, modulation, mixing, and limitations, etc., it is a wide range of applications. Compared to the facet type, the forward and reverse characteristics of the point contact diode are poor, so that the large current and rectification cannot be used.
Production Process: One end of the fine aluminum wire is connected to the anode lead and the other end is pressed on the doped N-type semiconductor. After adding the voltage, the fine aluminum wire melts and penetrates into the melted portion at the contact point. Thus, the contact point is actually a p-type semiconductor, and attached to the n-type semiconductor forming a PN junction.
02 surface contact diode
The "PN knunt" of the surface contact diode is large, allowing through a large current (several to dozens of mating), mainly used to convert the AC power converted into direct current "rectified" circuit. The surface contact type crystal diode is compared to a large current switch.
Planar diode
Planar diodes are a special silicon diode, named in the surface of the semiconductor. Initially, the semiconductor material used is formed by an epitaxial method, so it is referred to as an epitaxial plane type.
On the semiconductor single wafer (mainly N-type silica single wafer), the P-type impurity is diffused, and the shield of the surface oxide film surface of the silicon wafer is selectively proliferated on the N-shaped silica monoform. PN junction. The surface of the oxide film is covered by the surface of the PN-bonded surface, the stability is good and the life is long.
It can not only pass through a large current, but also to be stable and reliable, mostly in switches, pulses, and high frequency circuits.
Main characteristics of crystal diode
The voltammetry characteristic curve of the diode is as follows:
When the external voltage UW direction is p → n, UW is greater than the start voltage, diode conductation;
When the external voltage UW direction is N → P, UW is greater than the reverse breakdown voltage, the diode breakdown.
Crystal diode performance parameters
Maximum rectifier Current IDM: Diode continuous work allows the maximum forward current to pass; the current is too large, the diode will be burned by overheating; the large current stream can be loaded with a heat sink.
Maximum reverse voltage URM: URM is generally smaller than the reverse breakdown voltage, the selection specification is subject to URM, and there is a margin; overvoltage is easily damaged diode.
Reverse saturation current IS: Diode is applied to the current value when the reverse voltage; the IS reverse breakdown is small, the change is small; the IS will increase, generally, generally, at room temperature, silicon tube IS. 1881.1μA, germanium IS = 30 ~ 300μA.
The highest operating frequency fm: refers to the highest operating frequency of good working characteristics.
Different diode differences in different purposes
01 rectifier diode
The current directionality of most diodes We are generally called "Rectify" function, converting AC power to DC power.
Face contact structure, multi-use silicon material, can withstand largeient forward current and high reverse voltage. Performance is more stable, but due to the large compass, it is not advisable to operate in the high frequency circuit, so it cannot be used as a check tube. Metal and plastic packaging.
02 detection diode
The detecting diode is a device for detecting a low frequency signal superposed on a high frequency carrier, which has a high detection efficiency and good frequency characteristics.
The tantalum material point contact type, the operating frequency can reach 400 MHz, the forward pressure drop is small, the tone capacity is small, the detection efficiency is high, the frequency characteristics is good, and is 2ap.
Similar to the diode used in the case of detecting, in addition to the detection, it is also possible for limited, clipping, modulation, mixing, switching and other circuits. There are also two diode assemblies that are consistently consistent for the characteristics of the frequency modulation detection.
A glass package or ceramic housing package is used to obtain a good high frequency characteristic.
03 switch diode
Switch diodes are one of the semiconductor diode, which is a class of diodes specially designed to be manufactured on circuitry "opening" and "off". It is shorter than that of the general diode due to turning on the turbine or by the interpretation to turn.
The barrier capacitance of the switch diode is generally extremely small, which is equivalent to blocking the barrier capacitance, achieving the effect of maintaining a good one-way conductivity under high frequency conditions.
The time called the switch diode from the cut-off (high-resistance state) to the turning (low-resistive state); the time is called reverse recovery time from the turn-on to the cutoff; two times, the sum of the switching time. Generally, the reverse recovery time is greater than the opening time, so only the reverse recovery time is given on the use parameters of the switch diode. The switching speed of the switch diode is quite fast, and only a few nanths like a silicon switch diode, even the germanium switching diode, alever, only a few hundred nanoseconds.
The switch diode has a fast switching speed, small size, long service life, and high reliability, and is widely used in switch circuits, detective circuits, high frequency and pulse rectifier circuits and automatic control circuits for electronic devices.
04 regulator diode
The regulator diode refers to the use of a PN junction, and the current can change in a large-scale change and the voltage that is substantially unchanged, and the active diode is made.
The forward characteristics of the voltammetry curve of the regulator diode are similar, and the reverse characteristic is that the reverse resistance is large when the reverse voltage is lower than the reverse breakdown voltage, and the reverse leakage current is small. However, when the reverse voltage is adjacent to the critical value of the reverse voltage, the reverse current is suddenly increased, called breakdown.
05 beam diode
Varctor Diodes, also known as "variable electrical anti-diode". The material is more silicon or gallium arsenide single crystal, and an epitaxial process technology is employed.
It uses a diode made of a dependency and principle of a PN junction capacitor (barrier capacitor) and its reverse bias voltage VR, which is shown below.
The action of the variable diode is a semiconductor device made by the principle of capacitance between the PN junction, and is used in high-frequency tuning, communication and other circuits.
The variable diode belongs to the anti-bias diode, changing the reverse bias of its PN junction, can change the PN toner capacity. The higher the reverse bias, the less the bonding capacitance, the relationship between the reverse bias and the tonar capacitance is non-linear.
The relationship between the capacitance value and the reverse bias value of the variable diode:
The reverse bias is increased, resulting in a reduction in capacitance;
The reverse bias is reduced, resulting in an increase in capacitance;
The anti-polarization voltage is solarmed, then the toner is small.
06 light emitting diode
The light emitting diode is simply referred to as LED. It is made of a compound containing gallium gallium (Ga), arsenic (AS), phosphorus (P), nitrogen (N).
Visible light can be radiated when electrons are composite to holes, and thus can be used to make light-emitting diodes. The arsenide diode is red light, the gallium biological diode is green, the silicon carbide diode is yellow, and the gallium nitride diode is blue. An organic light emitting diode LED is divided by chemical properties.
07 Damping Diode
Damping diodes are similar to high frequency, high-pressure rectifier diode, which is characterized by lower voltage reduction and higher operating frequencies, and can withstand higher reverse breakdown voltages and large peak currents.
The damping diode is mainly used in a television set as a damping diode, a boost rectifier diode or a large current switch diode.
08 diode core group
Rectifier Bridge Heap (Half Bridge, All Bridge):
High pressure silicon stack (multiple silicon diode series):
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