Performance and characteristics of Fast recovery Diode

1.  Reverse recovery time.
   The definition of reverse recovery time (tr): the time interval at which the current is converted from a positive to a specified low value through zero. It is an important technical index to measure the performance of high frequency continuous current and rectifier devices. The waveform of the reverse recovery current is shown in figure 1. IF is the forward current and IRM is the maximum reverse recovery current. Irr is a reverse recovery current, which usually specifies Irr=0.1IRM. When t ≤ t0, the forward current I=IF. When t > t0, because the forward voltage on the rectifier device suddenly becomes the reverse voltage, the forward current decreases rapidly. At the time of t=t1, the forward current decreases rapidly. Then the reverse current IR flows through the rectifier, and the IR increases gradually, and the maximum reverse recovery current IRM is reached at the time of t=t2. After that, under the action of forward voltage, the reverse current decreases gradually and reaches the specified value Irr at the time of t=t3. The reverse recovery process from T2 to T3 is similar to the discharge process of capacitors.
   two。. Structural characteristics.
   The internal structure of the fast recovery diode is different from that of the ordinary diode. it adds base I between P-type and N-type silicon materials to form P-I-N silicon wafers. Because the base is very thin and the reverse recovery charge is very small, not only the trr value is greatly reduced, but also the transient forward voltage drop is reduced, so that the diodee can withstand a high reverse working voltage. The reverse recovery time of the fast recovery diode is generally hundreds of nanoseconds, the forward voltage drop is about 0.6 V, the forward current is several amperes to thousands of amperes, and the reverse peak voltage can reach hundreds to thousands of volts. The reverse recovery charge of the ultrafast recovery diode is further reduced, so that its trr can be as low as tens of nanoseconds. Most of the fast recovery and ultrafast recovery diodes below 20A are in the form of TO-220 package. From the internal structure, it can be divided into two types: single diodee and pair diodee (also known as double diodee). The diodee contains two fast recovery diodes, which can be divided into common cathode pair and common yang pair according to the different connection methods of the two diodes.
   3. Matters needing attention.
   1. Some single diodees have a total of three pins, with empty pins in the middle, which are usually cut off when leaving the factory, but some are not cut.
   two。. If one of the diodees is damaged, it can be used as a single diodee.
   3. The R × 1 gear must be used when testing the pressure drop of the correct guide. If the R × 1k gear is used, because the test current is too small, much lower than the normal working current of the diodee, the measured VF value will be obviously on the low side. In the above example, if the R × 1k measurement is selected, the forward resistance is equal to 2.2k Ω. The VF calculated from this is only 0.27V, which is much lower than the normal value (0.6V).