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What are the differences between fast recovery diodes and switching diodes

Fast recovery diode structure: Some adopt PN junction structure, while others adopt improved PIN structure. Its forward voltage drop is higher than that of ordinary diodes (0.5-2V), and its reverse voltage withstand is mostly below 1200V. In terms of performance, it can be divided into two levels: fast recovery and ultra fast recovery. The former has a reverse recovery time of hundreds of nanoseconds or longer, while the latter has a recovery time of less than 100ns (nanoseconds).

Schottky diode is a diode based on the potential barrier formed by the contact between metals and semiconductors, abbreviated as Schottky Barrier Diode. It has a forward voltage reduction (0.4-1.0V), a short reverse recovery time (2-10ns nanoseconds), and a large reverse leakage current, low withstand voltage, generally below 150V. It is mostly used in low voltage situations. The difference between Schottky diodes and fast recovery diodes is that the recovery time of the former is about 100 times smaller than that of the latter, while the reverse recovery time of the former is about a few nanoseconds!

The former has the advantages of low power consumption, high current, and ultra high speed! Of course, the electrical characteristics are all diodes! fast recovery diodes are manufactured using processes such as gold doping and simple diffusion, which can achieve high switching speed and high voltage resistance. Currently, fast recovery diodes are mainly used as rectifier components in inverter power supplies

Schottky diode: The reverse voltage withstand value is low (generally less than 150V), the on state voltage drop is 0.3-0.6V, and the reverse recovery time is less than 10nS. It is a diode with Schottky characteristics known as a "metal semiconductor junction". Its forward starting voltage is relatively low. In addition to materials, the metal layer can also be made of materials such as gold, molybdenum, nickel, and titanium. Its semiconductor material is silicon or gallium arsenide, mostly N-type semiconductor. This device is conductive by most carriers, so its reverse Saturation current is much larger than that of PN junction conductive by a few carriers. Due to the minimal storage effect of minority carriers in Schottky diodes, their frequency response is only limited by the RC time constant, making them ideal devices for high-frequency and fast switching. Its operating frequency can reach 100GHz. Moreover, MIS (metal insulator semiconductor) Schottky diodes can be used to make solar cells or light emitting diodes.

Fast recovery diode: With a forward conduction voltage drop of 0.8-1.1V and a reverse recovery time of 35-85nS, it quickly switches between conduction and cutoff, increasing the frequency of device use and improving the waveform. The fast recovery diode adopts gold doping and simple diffusion processes in its manufacturing process, which can achieve high switching speed and high voltage resistance. At present, fast recovery diodes are mainly used as rectifier components in inverter power supplies.

Fast Recovery Diode (FRD) is a new type of semiconductor device that has emerged in recent years. It has advantages such as good switching characteristics, short reverse recovery time, large forward current, small size, and easy installation. The Superfast Recovery Diode (SRD) is developed on the basis of the fast recovery diode, and its reverse recovery time trr value is close to the indicator of Schottky diodes. They can be widely used in switching power supply, pulse width modulator (PWM), uninterruptible power supply (UPS), AC motor variable frequency speed regulation (VVVF), high-frequency heating and other devices, as high-frequency, large current Flyback diode or rectifier , and are very promising power and electronic semiconductors.

1. Performance characteristics

Reverse recovery time

The definition of reverse recovery time tr is the time interval during which the current transitions from positive to a specified low value through zero. It is an important technical indicator for measuring the performance of high-frequency continuous current and rectifier devices. IF is the forward current, and IRM is the maximum reverse recovery current. Irr is the reverse recovery current, usually specified as Irr=0.1IRM. When t ≤ t0, the forward current I=IF. When t>t0, the forward voltage on the rectifier suddenly changes to the reverse voltage, resulting in a rapid decrease in forward current. At t=t1, I=0. Then the reverse current IR flows through the rectifier component, and the IR gradually increases; Reaching the maximum reverse recovery current IRM value at time t=t2. Afterwards, under the action of forward voltage, the reverse current gradually decreases and reaches the specified value Irr at t=t3. The reverse recovery process from t2 to t3 is similar to the capacitor discharge process.

2) The structural characteristics of fast recovery and ultra fast recovery diodes differ from ordinary diodes in that the internal structure of fast recovery diodes increases the base region I between P-type and N-type silicon materials, forming P-I-N silicon wafers. Due to the thin base region and small reverse recovery charge, not only does it greatly reduce the TRR value, but also reduces the transient forward voltage drop, enabling the to withstand a high reverse operating voltage. The reverse recovery time of fast recovery diodes is generally several hundred nanoseconds, with a forward voltage drop of about 0.6V, a forward current of several amperes to several thousand amperes, and a peak reverse voltage of several hundred to several thousand volts. The reverse recovery charge of the ultrafast recovery diode is further reduced, allowing its trr to be as low as tens of nanoseconds.

Fast recovery and ultra fast recovery diodes below 20A are mostly packaged in TO-220 format. From the perspective of internal structure, it can be divided into two types: single and double (also known as double ). The inner part of the pair contains two fast recovery diodes, which can be divided into a common cathode pair and a common anode pair according to the different connection methods of the two diodes. Figure 2 (a) shows the appearance and internal structure of the C 20-04 fast recovery diode (single transistor).

fast recovery diodes with tens of amperes are generally packaged in TO-3P metal shells. Pipes with larger capacities (from a few hundred amperes to several thousand amperes) are packaged in bolted or flat form.

2. Detection method

1) Measure reverse recovery time

The specified IF is supplied by a DC current source, and the pulse generator passes through a DC isolation capacitor C and adds a pulse signal. The trr value observed using an electronic oscilloscope is the time it takes from the time I=0 to the time IR=Irr.

Assuming the reverse recovery charge inside the device is Qrr, there is a relationship: trr ≈ 2Qrr/IRM. When the IRM is a certain value, the smaller the reverse recovery charge, the shorter the reverse recovery time.

2) Conventional testing methods

Under amateur conditions, a multimeter can be used to detect the unidirectional conductivity of fast recovery and ultra fast recovery diodes, as well as the presence of internal open circuit and short circuit faults, and to measure the forward conduction voltage drop. If equipped with a megohmmeter, it can also measure the reverse breakdown voltage.

Example: Measure an ultra fast recovery diode with the main parameters of trr=35ns, IF=5A, IFSM=50A, VRM=700V. Set the multimeter to R × First gear, read the forward resistance as 6.4 Ω, n '=19.5 grid; The reverse resistance is infinite. Further obtain VF=0.03V/grid × 19.5=0.585V. Prove that the pipe is good.

Precautions:

1、 Some single s have three pins, with an empty pin in the middle. They are usually cut off at the factory, but there are also some that are not cut off.

2、 If one of the pipes is damaged, it can be used as a single pipe.

3、 When measuring the pressure drop of the guide, R must be used × 1st gear. If R is used × At 1k gear, due to the low test current, which is much lower than the normal working current of the , the measured VF value will be significantly lower. In the above example, if R is selected × When measured at 1k level, the forward resistance is equal to 2.2k Ω, at which point n '=9 bars. The calculated VF value is only 0.27V, much lower than the normal value (0.6V).