When it comes to low-power, high-current and ultra-high-speed semiconductor devices, many students must first think of Schottky diode (SBD). But can you really use Schottky diodes? Compared with other diodes, what is special about Schottky diodes? Let's draw the key points together.
Key parameters of Schottky diode
Schottky diodes are widely used in switching power supply, frequency converter, driver and other circuits. In different applications, different factors need to be considered, and different devices have different performance. Therefore, when selecting Schottky diodes, the following key parameters need to be comprehensively considered.
1. On voltage drop (VF)
VF is the voltage drop across the diode when the diode is conducting in the forward direction. When the current through the diode is larger, VF is larger; When the diode temperature is higher, VF is smaller.
2. Reverse saturated leakage current (IR)
IR refers to the current flowing through the diode when the reverse voltage is added at both ends of the diode. The reverse leakage current of the Schottky diode is large, and the Schottky diode is selected as far as possible.
3. Rated current (if)
It refers to the average current value converted according to the allowable temperature rise when the diode operates for a long time.
4. Maximum surge current (IFSM)
Excessive forward current allowed to flow. It is not the normal current, but the instantaneous current, which is quite large.
5. Maximum reverse peak voltage VRM
Even if there is no reverse current, as long as the reverse voltage is continuously increased, the diode will be damaged sooner or later. The reverse voltage that can be applied is not an instantaneous voltage, but a forward and reverse voltage that is repeatedly applied. Since AC voltage is applied to the rectifier, its maximum value is an important factor specified. The maximum reverse peak voltage VRM refers to the maximum reverse voltage that can be applied to avoid breakdown. At present, the highest VRM value of Schottky is 150V.
6. Maximum DC reverse voltage VR
The maximum reverse peak voltage is a peak voltage repeatedly applied, and VR is a value when a DC voltage is continuously applied. For DC circuit, the maximum DC reverse voltage is very important to determine the allowable value and the upper limit value
7. Maximum operating frequency FM
Due to the existence of the junction capacitance of the PN junction, when the operating frequency exceeds a certain value, its unidirectional conductivity will become poor. The FM value of Schottky diode is high, up to 100GHz.
8. Reverse recovery time TRR
When the operating voltage changes from the forward voltage to the reverse voltage, the ideal condition of the diode operation is that the current can be cut off instantaneously. In fact, it usually takes a little time. The amount that determines the current cutoff delay is the reverse recovery time. Although it directly affects the switching speed of the diode, it is not necessary to say that this value is small. That is, when the diode is suddenly reversed from conduction, the reverse current is attenuated from great to near IR. This indicator is very important when the high-power switch operates in the high-frequency switching state.
9. Maximum dissipation power (P)
If there is current flowing in the diode, it will absorb heat and raise its temperature. In practice, the external heat dissipation has a great influence on P. Specifically, the voltage applied across the diode is multiplied by the current flowing and the reverse recovery loss.
