Selection of shcottky diodes

Schottky diode is an important device for the production of electronic products, because it carries the important role of the protection circuit, so it is particularly indispensable, we all know that when choosing Schottky diode, mainly look at its forward voltage drop, reverse withstand voltage, reverse leakage current, etc.

However, we rarely know how these relationships are at different currents, different reverse voltages, and different ambient temperatures, and knowing these relationships in circuit design is extremely important for choosing the right Schottky diode, especially in power circuits. Knowing its characteristics, it is more convenient for us to use, and here is a look at the characteristics of Schottky diodes.

1. The relationship between forward conduction voltage drop and on-current

When a forward bias voltage is applied across a v, its internal electric field region narrows, allowing a large forward diffusion current to pass through the PN junction.

Only when the forward voltage reaches a certain value (this value is called the "threshold voltage", germanium  is about 0.2V, silicon  is about 0.6V) can the Schottky diode really turn on. When price conditions permit, try to choose a SCHOTT diode with a small on-voltage drop and a rated operating current twice as high as the actual current.

2. The relationship between the positive conduction voltage drop and the temperature of the environment

In the process of developing our products, the influence of high and low temperature environment on electronic components is the biggest obstacle to the stable work of products. The influence of ambient temperature on most electronic components is undoubtedly huge, and Schottky diode are no exception, in high and low temperature environments: the on-voltage drop of Schottky diodes is inversely proportional to the ambient temperature.

Although the on-voltage drop is maximum at -45°C ambient, it does not affect the stability of the Schottky diode, but at 75°C the case temperature exceeds the 125°C specified in the data sheet, and the diode must be derated at 75°C. This is also one of the factors why switching power supplies need to be derated at a certain high temperature point.

3. The relationship between Schottky diode leakage current and reverse voltage

When a reverse voltage is applied across a Schottky diode, its internal electric field area widens, and less drift current passes through the PN junction, forming what we call leakage current.

Leakage current is also an important parameter to evaluate the performance of Schottky diode, Schottky diode leakage current is too large not only to increase its own temperature, for the power circuit will also affect its efficiency, different reverse voltage leakage current is different, the relationship is shown: the greater the reverse voltage, the larger the leakage current, at room temperature Schottky diode leakage current can be ignored.

4. The relationship between Schottky diode leakage current and ambient temperature

In fact, the biggest influence on the leakage current of Schottky diode is the ambient temperature, which is the relationship curve tested under rated back voltage, from which it can be seen that the higher the temperature, the greater the leakage current.

Rising in a straight line after 75°C, the leakage current at this point is one of the two major factors that cause the SCHOTT diode case to reach 125°C at rated current, and only by derating the reverse voltage and forward current can the operating temperature of the Schottky diode be reduced.