Do you know 4 characteristics of Schottky diodes?
The Schottky diode is an important electronic component, because it plays an important role in protection circuit, it is especially indispensable. We all know that when choosing a Schottky diode, it mainly depends on its forward conduction Voltage drop, reverse withstand voltage, reverse current leaks, etc.
But we rarely know what its ratio is at different currents, different reverse voltages and different ambient temperatures. Knowing these ratios in circuit design is extremely important for choosing right Schottky diode, especially in a power circuit. It is more convenient for us to know its characteristics. In next article, you will get acquainted with mysterious characteristics of Schottky diodes.
Relationship between direct conduction voltage drop and conduction current
When a forward bias voltage is applied to both ends of a Schottky diode, its internal electric field area shrinks and a large forward diffusive current can flow through PN junction.
Only when forward voltage reaches a certain value (this value is called “threshold voltage”, a germanium lamp is about 0.2 V and a silicon lamp is about 0.6 V), Schottky diode can actually conduct current.
But is conduction voltage drop of a Schottky diode constant? What is relationship between it and direct diffusion current? Using test circuit shown in figure below, SM360A Schottky diode model is tested at room temperature. The diode conducts a test for relationship between conduction current and conduction voltage drop, and shown relationship curve can be obtained: direct conduction voltage drop is proportional to conduction current, and floating voltage difference is 0.2V.
Although voltage difference from light load conduction current to rated conduction current is only 0.2V, for high-power Schottky diodes, this affects not only efficiency, but also temperature rise of Schottky diodes, so in terms of price, try to choose if possible Schottky diode with a low conduction voltage drop and a rated operating current twice actual one.
Relationship between forward voltage drop and ambient temperature
In process of developing our products, exposure to high and low temperatures on electronic components is biggest obstacle to stable operation of products.
The effect of ambient temperature on most electronic components is undoubtedly enormous, and Schottky diodes are no exception. In high and low temperature conditions, we can know this from measured performance curve of SM360A: Schottky Diodes The conduction voltage drop is inversely proportional to ambient temperature.
Although conduction voltage drop is maximum at an ambient temperature of -45°C, it does not affect stability of Schottky diode, however, at an ambient temperature of 75°C, case temperature exceeded 125°C. given in data sheet ℃, diode rating should be derated at 75℃. This is also one of factors why switching power supplies should be reduced at a certain high temperature point.
Relationship between Schottky diode leakage current and reverse voltage
When a Schottky diode is reversed, its internal electric field area becomes wider, and less drift current flows through PN junction, creating what we call leakage current.
Leakage current is also an important parameter for evaluating performance of Schottky diodes. Excessive leakage current of Schottky diodes not only increases their own temperature, but also affects their efficiency for power circuits. Leakage at different reverse voltages The current is different, as shown in relationship: larger reverse voltage, larger leakage current, and leakage current of Schottky diode can be neglected at room temperature.
Relationship between Schottky diode leakage current and ambient temperature
In fact, ambient temperature has greatest influence on leakage current of Schottky diode, which is a curve tested at nominal backpressure. It can be seen from it that higher temperature, greater leakage current.
After 75 °C, it increases in a straight line. The leakage current at this point is one of two main factors that cause body temperature of Schott diode to reach 125°C at rated current. Only by reducing reverse current can voltage and forward conduction current be reduced across the Schott diode Teky diode operating temperature.
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