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 at both sides of the interface, and a self-built electric field is built. When there is no applied voltage, the diffusion current caused by the difference of the carrier concentration on both sides of the pn junction is equal to the drift current caused by the self-built electric field and is in the electric equilibrium state. When the outside world is biased by the forward voltage, mutual suppression of the external electric field and the self-built electric field increases the diffusion current of the carrier and causes a forward current. When the outside world 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 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 intensity in the space charge layer of the pn junction reaches a critical value to generate a doubled charge carrier process, generating a large number of electron-hole pairs, resulting in a large reverse breakdown current This is called the diode breakdown phenomenon.
What is the role of the diode?
The application of the diode in the circuit is indispensable, and it will be used whether it is a rectifier circuit or a clamp or some other function.
Diodes can be divided into light emitting diodes (LEDs), rectifier diodes, zener diodes, switching diodes, etc. Here are just a few of the above mentioned.
Light-emitting diodes are believed to have been seen by everyone. They are generally used as indicator lights. For example, a computer's hard disk light flashes to indicate that your hard disk is working. (If it does not flash, it may be that your machine is too busy or is on standby. State), there are some indicators on the Walkman, and the charger's indicator. LED forward voltage is relatively large compared to other diodes, generally between 1.6V to 1.8V. Two other diodes are generally 0.2-0.3 V (mandrel), 0.6-0.8V (silicon tube).
Rectifier diodes, which are also very common, use the unidirectional conduction characteristics of the diodes, so that negative-polarity electrical signals can be filtered out—half-wave rectification, as well as other rectification—for example, full-wave rectification.
The diode also has a voltage stabilizing effect, because when the diode is reversely turned on, the current will increase instantaneously when the diode is broken, so that when the external voltage increases, the increased current due to the breakdown of the diode will Via a diode without passing through a load in parallel with the diode, it is possible to protect the device in parallel with it. A common protective field effect transistor is a diode in the opposite direction of the gate of the field effect transistor. Diode breakdown voltage is generally 4V-7V.
Clamping action: The clamping action is to maintain the diode's forward voltage at 0.2-0.4V (funnel) and 0.6-0.8V (silicon) after conduction, so that the voltage across the connected device is maintained at Within a range, the simplest is that the BE junction voltage of the transistor can be kept at the clamping voltage when it is turned on. This is often used for the static analysis of the triode. It is generally not specified that the silicon tube should be taken as 0.7V and the helium tube should be taken as 0.3V.
The common types of switching diodes are 1N4148, 1N4150, and 1N4448, which use the high-speed switching characteristics of the diode. Limited to the level, will not be described in detail.
Other diodes include Schottky diodes, tunnel diodes, bidirectional start diodes, micropower reference voltage diodes, and the like, and have different functions due to their different manufacturing processes.
