How to distinguish between field effect transistors and Schottky diodes?

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How to distinguish between field effect transistors and Schottky diodes? [Copy link]

Schottky diodes have been favored and liked by users since they replaced traditional ordinary diodes. However, sometimes people can be foolish and confused. What is the difference between Schottky diodes and field-effect transistors?
　　Schottky diodes are diodes, which are characterized by low power consumption, ultra-high speed, extremely short reverse recovery time, and small forward voltage drop, making them suitable for rectifier circuits; field-effect transistors are triodes, which are characterized by high input impedance, low noise, low power consumption, small leakage current, and good switching characteristics, making them suitable for amplifier circuits or switching circuits.
　　Diodes and triodes are completely two different types and cannot be compared, but they belong to the same category of electronic components.
　　The appearance of Schottky diodes and ordinary diodes or field-effect transistors is more or less similar, so it is inevitable that users will be confused when using them.

　　

　　What is a field effect tube?
　　Field effect tube is the abbreviation of field effect transistor, which should be abbreviated as FET. Field effect tubes are usually divided into two categories: 1) JFET and MOSFET. Both types of field effect tubes are voltage-controlled devices. Field effect tubes have three electrodes, namely: gate G, drain D and source S. At present, MOSFET is widely used, while JFET is relatively rare. MOSFET can be divided into NMOS and PMOS. The following figure is the structure diagram of PMOS, and the circuit symbol diagram of NMOS and MOSFET.

　　

The structure of PMOS is as follows: Two P+ regions of P-type semiconductor are made on the N-type silicon substrate. These two regions are called source S and drain D respectively, and the gate G is led out on the insulating layer of the N-type semiconductor. The physical picture and pin distribution of NMOS are shown in the figure below.

　　

What is a Schottky diode?
　　Schottky diode, also known as barrier diode, is a diode formed by the contact between metal and semiconductor. Its characteristics are:
　　the reverse recovery time is very short, at the ns level;
　　the forward conduction voltage drop is very low: about 0.3-0.5V;
　　the leakage current is large and the reverse breakdown voltage is relatively low; it
　　is usually used in low-voltage switching power supplies. Taking Schottky diode MBR30100 as an example, its physical diagram and structure diagram are shown in the figure below.

　　

The Schottky diode has three electrodes, one of which is the cathode, and is composed of two diodes with a common cathode. What
　　about the problem of the reverse parallel diode of the field effect tube?
　　Some field effect tube specifications have a voltage regulator tube symbol on the schematic diagram. In order to find out the real situation, we have selected several samples with the diode symbol for testing and found the following two situations:
　　1. It is actually a parasitic diode of the body; 2. The integrated Schottky diode

　　In the first case, it is probably because the graphics in other files were directly copied when the file was created. ? Regarding the characteristics of the diode, there should be specifications in the specification book. But please note that it is a diode, not a voltage regulator. Don't be confused by the graphics of the voltage regulator.
　　In the second case, please note that it is a Schottky diode, and the symbol marked in the figure is also wrong. Some components have such integration, and there must be relevant parameter descriptions in their parameter tables, namely: the voltage and current parameters of the Schottky diode. Everyone should pay attention to the relevant parameters when identifying components.

　　Another possibility is the voltage regulator characteristics of the marked field effect tube breakdown area.
　　Of course, as a manufacturer, they will not make any guarantee commitments for this characteristic of the field effect tube. Therefore, there is generally no description of its characteristics and parameter table in the specification book. The components cannot work in this area when actually used.
　　However, for different manufacturers, the tolerance of components is different. Some originals are easily damaged after exceeding the breakdown voltage, while some components can withstand the impact of higher breakdown current, which, in some occasions, determines the user's perception of component quality.
　　Table, and pay attention to the difference with the body diode parameters. If correct, it means that there is a parallel diode, otherwise it is a graphic error.