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www.us - tech.com Surge Protection: Keeping


COMPLETE SOLUTIONS


for Soldering Processes and Automated


Production Lines 


Voltage Spikes Under Control... Continued from page 52


gy with a PN junction that has a defined breakdown voltage. When a transient input voltage exceeds the breakdown voltage, a current flows through the TVS diode to provide protection against transient voltages. However, the TVS type with a PN junction has no minority carriers and therefore exhibits poor clamping characteristics due to its high internal resistance. In semiconductor technology, there are alternative TVS implementations with bipolar NPN/PNP junctions,


March 2026





Figure 3: characteristic VI curve of bidirectional TVS diodes with snapback effect.





in which a bipolar transistor is triggered by an avalanche effect for the clamping characteristic. When this avalanche current moves toward the base of the par-





asitic BJT, the base current can open the BJT and allow a large cur- rent to flow between the collector and emitter. The most interesting thing about this is that after opening, i.e., triggering the device, the high electric field that started the process is no longer necessary or even present to maintain the current. The conduction of current con- tinues as the current increases, but at a much lower voltage between the emitter and collector. This phenomenon of triggering at a rela- tively high voltage and then falling back into conductivity at a lower voltage is called snapback. Figure 3 shows the current-voltage characteristics of unidirec-


tional and bidirectional TVS diodes with snapback effect. For effec- tive ESD protection, the trigger voltage should not be so high that it damages the circuit to be protected. In addition, the lower hold volt-





age Vhold should be above the normal operating voltage of the circuit, which is ensured if the maximum operating voltage VDC or VCh is not exceeded. If the TVS diode is not selected correctly, there is a risk of


so-called latch-up. A voltage-limiting component must provide protection against





SMART SYSTEMS with PURE EFFICIENCY


transient events without impairing the desired operation of the cir- cuit. This can be challenging, as the parameters are often in conflict with each other. A TVS diode for high-frequency signal interfaces should have low capacitance to avoid signal interference from capac- itive load. However, a component’s ability to absorb energy depends on the size of the barrier layer. The larger the barrier layer, the more energy it can absorb. The disadvantage is that as the size of the bar- rier layer increases, so does the capacitance of the component. A com- mon method of reducing the effective capacitance is to use a low-ca- pacitance diode circuit. To protect multiple symmetrical signal buses such as USB 3.1,


several diode circuits are combined into an “array.” The capacitance of the TVS diode is effectively “hidden” by the


conventional diodes upstream of the circuit. The diodes must with- stand the transient current and require a reverse breakdown voltage that is greater than the breakdown voltage of the TVS diode. Contact: Würth Elektronik eiSos GmbH & Co. KG, Clarita-Bernhard-Strasse 9, 81249 Munich, Germany % +49-7942-945-5186 E-mail: sarah.hurst@we-online.de Web: www.we- online.de r


 


See at APEX Expo, Booth 3100


For further information, see application note ANP143 from Würth Elektronik.


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