release time:2022-03-03Author source:SlkorBrowse:1132
TVS tube unidirectional and bidirectional
1. Look at the signs: tvs tubes are divided into one-way and two-way. One end of the one-way has a thin color ring, which is connected to the positive pole, while the two-way tube has two rings in the middle, or there is no sign, no pole sex.
2. Look at the specifications: generally on the first page, two-way is two-way conduction, one-way is one-way conduction.
3. Look at the model: the model name of the tvs tube is regular, and most of the tvs tube models can see the parameters. For example, the TVS tube SMBJ5.0A/SMBJ5.0CA, the suffix followed by A means unidirectional, and the suffix CA means bidirectional.
4. With the help of a multimeter tool: one side has voltage on one side, and the DC side has avalanche breakdown characteristics; both sides have voltage, and the DC side has two-way symmetry.
1. VRWM: When the circuit is working normally, the TVS diode does not work and is in the cut-off state, so the cut-off voltage of the TVS diode should be greater than the maximum working voltage of the protected circuit. In this way, it can be ensured that the TVS will not affect the circuit operation under the normal operation of the circuit. However, the working voltage of the TVS diode also determines the clamping voltage of the TVS diode. When the cut-off voltage is greater than the normal working voltage of the line, the working voltage of the TVS diode cannot be selected too high. If it is too high, the clamping voltage will also be Therefore, when selecting VRWM, the operating voltage of the protected circuit and the bearing capacity of the subsequent circuit should be comprehensively considered.
3. VC clamping voltage: The clamping voltage of the TVS diode should be less than the maximum transient safety voltage that the protected circuit of the latter stage can withstand. The VC of most TVS tubes is proportional to VBR and IPP. For TVS tubes of the same power level, the higher the breakdown voltage, the higher the VC.
4. IR leakage current: In some low-power circuits or high-precision acquisition circuits, excessive IR may lead to excessive circuit power consumption or excessive signal acquisition accuracy. Due to the large IR of the low-voltage (VRWM < 10V) TVS tube, if the post-stage circuit has a strong tolerance, try to choose a TVS tube with 10V or more; if the post-stage circuit has insufficient tolerance, it is necessary to choose a small IR and low voltage The TVS tube, Dongwo Electronics can provide such products.
5. C junction capacitance: The junction capacitance of TVS tubes is generally in the range of tens of picofarads to tens of nanofarads. For TVS tubes of the same power level, the lower the voltage, the larger the capacitance value. In some communication lines, special attention should be paid to the junction capacitance of the TVS tube, which cannot affect the normal operation of the circuit.
6. Package form: Generally speaking, the power of the TVS tube can also be reflected in the package form. The smaller the package size, the smaller the power. This is because the chip area of the TVS tube directly determines the power level of the TVS tube.
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