TVS tube function and its application circuit

The following points should be noted when calculating and selecting:

①The TVS rated reverse shutdown voltage VWM should be greater than or equal to the maximum operating voltage of the protected circuit.

②Minimum breakdown voltage VBR=VWM/KBR (where KBR=0.8～0.9).

③The maximum clamping voltage VC of TVS should be less than the damage voltage of the protected circuit, that is, VC=KC×VBR (where KC=1.3).

④ Within the specified pulse duration, the maximum peak pulse power consumption PM of the TVS must be greater than the peak pulse power that may appear in the protected circuit. After determining the maximum clamping voltage, its peak pulse current should be greater than the transient surge current.

The role of TVS tube

TVS tube is a high-efficiency protection device in the form of a diode. When the two poles of the TVS diode are subjected to a reverse transient high-energy impact, it can change the high impedance between the two poles into a low impedance at a speed of 10-12 seconds, absorb up to several kilowatts of surge power, and clamp the voltage between the two poles to a predetermined value, effectively protecting the precision components in the electronic circuit from damage by various surge pulses. Due to its advantages of fast response time, large transient power, low leakage current, small breakdown voltage deviation, easy to control clamping voltage, no damage limit, small size, etc., it has been widely used in computer systems, communication equipment, AC/DC power supplies, automobiles, electronic ballasts, household appliances, instruments, RS232/422/423/485, I/O, LAN, ISDN, ADSL, USB, MP3, PDAS, GPS, CDMA, GSM, digital camera protection, common mode/differential mode protection, RF coupling/IC drive reception protection, motor electromagnetic interference suppression, audio/video input, sensors/transmissions, industrial control circuits, relays, contactor noise suppression and other fields.

TVS tubes Comparison with varistors

At present, many devices in China that need surge protection use varistors. TVS tubes are generally used for protection against electrical fast transient pulse groups, and their characteristics are much better than those of varistors. The specific characteristic parameters are listed in Table 5.

Table 5 Comparison between TVS tube and varistor

Application Examples of TVS Tubes

AC Circuit

Figure 4 is a schematic diagram of a microcomputer power supply using a TVS tube for line protection.

Figure 4 Schematic diagram of microcomputer power supply

The line protection in Figure 4 is explained below.

① Add a bidirectional TVS tube D1 at the 220 V AC input line to suppress the peak interference in the 220 V AC power grid.

When selecting D1, the above parameters can be obtained by looking up the table.

② Add an anti-interference power line filter at the transformer input to eliminate small spike interference.

③ Add a bidirectional TVS tube D2 at the AC 20 V output end of the transformer to suppress interference again.

When selecting D2, the above parameters can be obtained by looking up the table.

④ When the rectifier and filter output DC 10 V, add the unidirectional TVS tube D3 to suppress interference.

When D3 is selected, the above parameters can be obtained by looking up the table.

Through the above four suppressions, the so-called "purified power supply" is obtained. In order to prevent surge voltages such as lightning strikes, a varistor can be added to the AC 220 V incoming line to more effectively prevent interference from entering the computer's CPU and memory, thereby further improving the reliability of the system.