1. The surface of the point contact tube is not easy to clean

Needle pressure can cause surface distortion of semiconductors

Its contact barrier is not an ideal Schottky barrier

When subjected to mechanical vibrations, it can also produce trembling noise. The surface fusion type tube metal semi touch page is relatively flat and not exposed, making it the easiest to clean

Its contact barrier is almost an ideal Schottky barrier.

2. Different point contact tubes have different crimping pressures during production

Make the diameter of Schottky junction different

Therefore, the performance consistency and reliability are poor. The surface combined pipe adopts flat technology

Therefore, it has stable performance, good consistency, and is not easily damaged. The structure diagram and equivalent circuit of a surface bonded diode are shown in the figure. It can be seen from this that the structural dimensions of each part are in the order of magnitude. Generally, these types of chips can be conveniently packaged for easy application. The typical packaging structure of Schottky barrier diodes can adopt "shell" type, microstrip type, SOT patch type, etc.

Q: How can Schottky diodes be distinguished from ordinary diodes in appearance? What is the difference in identification between Schottky diodes and ordinary diodes?

Answer: Apart from the model specifications, there is usually no difference in appearance design, but it can accurately measure the difference in forward pressure drop. Immediately use a digital multimeter to measure (small current). Generally, the second stage transistor is around 0.5V, and the Schottky diode is below 0.3V. When the current is large, the second stage transistor is generally around 0.8V, and the Schottky diode is below 0.5V; SR350 means expressing 3A50V. The voltage resistance of Schottky diodes is generally below 100V, and there are no ones above 150V.

What is a fast recovery diode?

Fast Recovery Diode (FRD) is a semiconductor material diode with good power switching characteristics and fast reverse recovery speed. It is mainly used in electronic circuits such as power transformers, PWM pulse width modulators, and soft starters as a high-frequency rectifier diode, freewheeling diode, or damping diode.

Internal structure of fast recovery diode

Unlike ordinary PN junction diodes, it belongs to the PIN junction type diode, which adds a base region I between P-type silicon material and N-type silicon material to form a PIN silicon wafer. Due to the thin base region and small reverse recovery charge, the fast recovery diode has a shorter reverse recovery time, lower forward voltage drop, and higher reverse breakdown voltage (withstand voltage value)

Generally speaking, fast recovery diodes aged 5-20 are packaged in TO-220FP plastic, high-power fast recovery diodes over 20 years old are packaged in TO-3P plastic with metal heat sinks on the top, and fast recovery diodes under 5 years old are packaged in DO-41, DO-15, or DO-27 specifications.

Choose TO-220 or TO-3P packaged power fast recovery diodes, which can be single tube or multi tube. The pin extraction methods of dual tubes are divided into co positive and co negative.

1. Performance characteristics

1. Reverse recovery time

The definition of reverse recovery time tr is the interval time during which the current changes from the forward direction to the required low value and is easily consumed based on the zero point. It is an important technical indicator for measuring the performance of high-frequency freewheeling 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 the reverse recovery current, usually specified as Irr=0.1IRM. When t ≤ t0, the forward current I=IF. When t>t0, due to the sudden change of the forward voltage on the rectifier device to the reverse voltage, the forward current rapidly decreases. At t=t1, I=0。 Then a reverse current IR flows through the rectifier device, and IR gradually increases; At time t=t2, the maximum reverse recovery current IRM value is reached. From then on, under the effect of the forward working voltage, the reverse current gradually decreases and exceeds the standard value Irr at t=t3. The reverse recovery process from t2 to t3 is similar to the discharge process of capacitors.

2) The structural characteristics of fast recovery and ultra fast recovery diodes

The internal structure of a fast recovery diode is different from that of a regular diode, as it adds a base region I between P-type and N-type silicon materials to form a P-I-N silicon wafer. Because the base region is too thin, the reverse recovery of positive charges is not significant, which not only greatly reduces the TRR value, but also reduces the transient forward pressure drop, allowing the water pipe to withstand high reverse operating frequencies. The reverse recovery time of a fast recovery diode is generally several hundred nanoseconds, the forward voltage drop is about 0.6V, the forward current is several amperes to several thousand amperes, and the peak reverse voltage can reach 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. From the perspective of internal structure, it can be divided into two types: single tube and double tube (also known as double tube). There are two fast recovery diodes inside the transistor, and according to the different wiring methods of the two diodes, there are also common cathode diodes and common anode diodes. Figure 2 (a) shows the external and internal structure of the C20-04 fast recovery diode (single tube). (b) The figure and figure (c) show the appearance and structure of C92-02 type (common cathode pair) and MUR1680A type (common anode pair) ultrafast recovery diodes, respectively. They are all packaged in TO-220 plastic,

Fast recovery diodes with tens of amps are generally packaged in TO-3P metal shells. For water pipes with larger space (several hundred to several thousand amperes), anchor bolt type or tablet type packaging type should be selected.