“Schottky diode is an important Electronic component. Because it carries the important role of protection circuit, it is especially indispensable. We all know that when choosing Schottky diode, it mainly depends on its forward voltage drop, Reverse withstand voltage, reverse leakage current, etc.
Schottky diode is an important electronic component. Because it carries the important role of protection circuit, it is especially indispensable. We all know that when choosing Schottky diode, it mainly depends on its forward voltage drop, Reverse withstand voltage, reverse leakage current, etc.
But we rarely know what the relationship is under different currents, different reverse voltages, and different ambient temperatures. Knowing these relationships in circuit design is extremely important for choosing the right Schottky diode, especially in power circuits. middle. Knowing its characteristics will make it easier for us to use. The following article will take you to explore the mysterious characteristics of Schottky diodes.
1. The relationship between forward conduction voltage drop and conduction current
When a forward bias voltage is applied to both ends of the Schottky diode, the internal electric field area becomes narrower, and a larger forward diffusion current can pass through the PN junction.
Only when the forward voltage reaches a certain value (this value is called the “threshold voltage”, the germanium tube is about 0.2V, and the silicon tube is about 0.6V), the Schottky diode can really turn on.
But is the conduction voltage drop of the Schottky diode constant? What is the relationship between it and the forward diffusion current? The Schottky diode model SM360A is conducted at room temperature through the test circuit shown in the figure below. Test the relationship between on-current and on-voltage drop, and the curve relationship shown can be obtained: the forward-on voltage drop is proportional to the on-current, and the floating voltage difference is 0.2V.
The voltage difference from the light-load conduction current to the rated conduction current is only 0.2V, but for power Schottky diodes, it not only affects the efficiency but also affects the temperature rise of the Schottky diodes, so if the price conditions allow, Try to choose a Schott diode with a small turn-on voltage drop and a rated operating current that is twice as high as the actual current.
2. The relationship between forward conduction pressure drop and ambient temperature
In the process of our product development, the impact of high and low temperature environments on electronic components is the biggest obstacle to the stable operation of the product. The influence of ambient temperature on most electronic components is undoubtedly huge. Schottky diodes are of course no exception. In high and low temperature environments, we can know from the relationship curve of the SM360A measured data sheet: the conduction of Schottky diodes. The pressure drop is inversely proportional to the ambient temperature.
When the ambient temperature is -45℃, although the conduction voltage drop is the largest, it does not affect the stability of the Schottky diode, but when the ambient temperature is 75℃, the case temperature has exceeded the 125℃ specified in the data sheet, then The diode must be derated for use at 75°C. This is also one of the factors why switching power supplies need to be derated for use at a certain high temperature point.
3. The relationship between Schottky diode leakage current and reverse voltage
When a reverse voltage is applied to both ends of the Schottky diode, the internal electric field area becomes wider, and there is less drift current through the PN junction, forming what we call leakage current.
Leakage current is also an important parameter to evaluate the performance of Schottky diodes. Excessive leakage current of Schottky diodes will not only increase its own temperature, but also affect its efficiency for power circuits. Leakage currents under different reverse voltages are different. , The relationship is shown: the greater the reverse voltage, the greater the leakage current, and the leakage current of the Schottky diode at room temperature can be ignored.
4. The relationship between Schottky diode leakage current and ambient temperature
In fact, it is the ambient temperature that has the greatest influence on the leakage current of the Schottky diode, which is the relationship curve tested under the rated back pressure. It can be seen from this: the higher the temperature, the greater the leakage current.
It rises in a straight line after 75°C. The leakage current at this point is one of the two major factors that cause the Schottky diode housing to reach 125°C under the rated current. Only by derating the reverse voltage and forward conduction current can the Schottky diode be reduced Working temperature.