diode main parameters: forward current. Forward voltage drop. Reverse breakdown voltage. Reverse leakage current. Junction capacitance, etc. The main characteristics of the diode: forward conduction, reverse cutoff. The main role of the diode: rectification. Voltage regulation. Freewheeling. Detecting. Switch. Classification of diodes:
1. According to the installation method: patch and plug-in, the difference is: A. SMD diode can be attached to the PCB by the placement machine, or soldered on the PCB by hand soldering. The type of the patch depends on the current. Different, the package size is different, such as: LL34. LL41. SOD123 SOD323 SOD523. DO-213AA.DO214-AC.SMA. SOT23, etc., B. The plug-in diode is either manually soldered or inserted on the board and then fixed by wave soldering. On the PCB, the size of the plug-in also varies according to the current, such as: DO-35. DO-41. TO-220, etc. In the design point of view, if the space and function are satisfied, the patch component is preferred. This reduces product costs.
2. Types of diodes: A. Working in forward conduction state such as: ordinary rectifier two tubes. Ultra-fast recovery diodes. Schottky diodes, LEDs, etc., B. Working in reverse breakdown state such as: Zener diode. TVS tube (transient suppression diode), etc.
3. Selection of diode: A. Ordinary rectifier diodes can be made very large due to low response speed, and the reverse voltage is very large. Generally, it is suitable for low-frequency, high-current and high-voltage rectifier circuits (50HZ/60HZ). B. Ultra-fast recovery diode due to fast reaction speed, large current, large reverse voltage, mostly used in high voltage, high frequency, high current rectifier circuit. C. Schottky diode, low power consumption. Fast speed. Large current. Reverse withstand voltage is slightly lower and used in the circuit of switching power supply output rectification and freewheeling. D. The voltage regulator tube is used to stabilize the voltage at a certain point, and the TVS is mainly used as the instantaneous impact protection of the circuit, and the reaction speed is fast and the bearing capacity is strong.
4. Diode selection: Mainly according to circuit characteristics such as: voltage, frequency, current, working environment to select the appropriate components. 5. Diode measurement: The multimeter only makes a simple good or bad measurement: if the multimeter is dialed to the diode measurement file, the two ends of the diode are respectively contacted with the meter head. When the meter head is connected in the forward direction, the value is displayed, and the reverse connection is displayed. There is no value. If you want to test specific parameters, you have to use special instruments. Many companies do not have such conditions. Therefore, we must choose brands and select quality suppliers when selecting models.