WEET How and What About TVS (Transient Voltage Suppressors) Diodes Knowledge

Author: admin　Publish: 2019/12/19　Category: Transient Voltage Suppressors　Read: Times　Comments

WEE Technology Company Limited 

Manufacturer of Surface Mount (SMD) and Through Hole (DIP) Diodes & Rectifiers    

TVS (Transient Voltage Suppressors) diodes, that is, transient voltage suppressors, also known as avalanche breakdown diodes, are single PN junction or multiple PN junction integrated devices made by semiconductor processes. There are unidirectional and bidirectional TVS diodes. Unidirectional TVS diodes are generally used in DC power supply circuits, and bidirectional TVS diodes are used in voltage alternating circuits. When applied to a DC circuit, a unidirectional TVS diode is connected in reverse in parallel to the circuit. When the circuit works normally, the TVS diode is in the off state (high-impedance state), which does not affect the normal operation of the circuit. When the circuit has an abnormal overvoltage and reaches the TVS diode breakdown voltage, the TVS diode quickly changes from a high-resistance state to a low-resistance state, releasing the transient overcurrent caused by the abnormal overvoltage to the ground, and clamping the abnormal overvoltage to Low level, thus protecting the post-stage circuit from abnormal overvoltage. When the abnormal overvoltage disappears, the resistance of the TVS diode returns to a high-impedance state.

First, TVS diode products supplied by WEET can be classified from the package types:

• SMA/DO-214AC：P4SMA6.8CA THRU P4SMA250CA, SMAJ5.0CA THRU SMAJ440CA

• SMB/DO-214AA：P6SMB6.8CA THRU P6SMB250CA, SMBJ5.0CA THRU SMBJ440CA

• SMC/DO-214AB：SMDJ5.0CA THRU SMDJ170CA, SMCJ5.0CA THRU SMCJ440CA

• SOD-123FL：SMF5.0CA THRU SMF220CA

• DO-41：P4KE6.8CA THRU P4KE440CA

• DO-15：P6KE6.8CA THRU P6KE600CA

• DO-27：1.5KE6.8CA THRU 1.5KE440CA

Second Part: What do TVS diode characteristics stand for ?

• Made of semiconductor technology, with high reliability and no damage limit;

• Glass passivation process, accurate on-voltage;

• Large transient power, low capacitance, low leakage current, easy to control clamping voltage;

• Fast response time: usually less than 1.0PS;

• Excellent clamping ability and small breakdown voltage deviation;

• High voltage accuracy, in special applications, higher accuracy can be achieved through process or parameter screening;

• Small size and easy installation;

• unidirectional and bidirectional units;

• Transient power can reach 200W-30000W or even higher under 10 / 1000μs waveform;

• Working voltage range 3.3V ~ 600V, or even higher;

• Diversified package formats

SMD package: SOD-123, SMA / DO-214AC, SMB / DO-214AA, SMC / DO-214AB, DO-218AB, etc.

In-line package: DO-41, DO-15, DO-201,  etc .;

• Halogen-free and RoHS compliant;

Third Part: How to understand TVS diode selection guide?

1) To determine the maximum DC or continuous operating voltage in the protected circuit, the rated standard voltage of the circuit and the "high-end" tolerance;

2) The rated transient power of the TVS tube is greater than the maximum transient surge power that may occur in the circuit;

3) The cut-off voltage of the TVS tube must be greater than the highest working voltage of the circuit being protected;

4) The maximum clamping voltage of the TVS tube should be less than the damage voltage in the protected circuit of the subsequent stage;

5) After determining the maximum clamping voltage of the TVS tube, its peak pulse current should be greater than the transient surge current;

6) For the circuit protection of the data interface, you should also pay attention to the selection of TVS diodes with appropriate capacitance. For example: when the signal frequency or transmission rate is high, a TVS tube with a low capacitance series should be selected;

Fourth Part:  WEET shares the detailed explanation of TVS diode parameters

• VRWM: cut-off voltage, the highest working voltage of TVS diode, the maximum DC voltage or AC peak voltage that can be continuously applied without causing degradation or damage of TVS diode Under VRWM, TVS diodes are not working and are not conducting.

• VC: Clamping voltage. The peak voltage measured across the TVS diode when the peak pulse current IPP of the specified waveform is applied.

• VBR: Breakdown voltage, which is the minimum avalanche voltage of a TVS tube. It refers to the voltage across the TVS measured on the V-I characteristic curve under the specified pulsed DC current IT or the current near the occurrence of avalanche.

• IR: Leakage current, also known as standby current. The maximum current flowing through a TVS diode at a specified temperature and maximum operating voltage is measured at the cutoff voltage.

• IPP: peak pulse current, generally the peak value under 10 / 100μs current waveform.

• IT: Test current.

• C: Capacitance value. For TVS tubes of the same power level, the lower the voltage, the larger the capacitance value. In the protection of communication lines, pay special attention to the capacitance value of the TVS tube.

• Package form: From the package form of the TVS tube, its power can be seen. The chip area of a TVS tube directly determines its power level.

Fifth Part:  How to choose TVS and TVS diode selection precautions

1) The specification manual only gives the absorbed power peak at a specific pulse width, and the pulse width in the actual circuit is variable. There must be a number in the heart, and the wide pulse should be derated.

2) For the protection of small current load circuits, it is necessary to intentionally increase the current limiting resistance;

3) Pay attention to whether the steady-state average power of the TVS diode is within the safe range;

4) Consider temperature changes. Normally, transient suppression diodes work between -55 ° C and 150 ° C. Derating should be applied when the temperature in the circuit is relatively high.

5) The lead length of TVS transient suppression diode should be opposite to the line to be protected.

6) For the protection in the data interface or communication line, TVS diodes with relatively small capacitance values should be selected as much as possible.

7) Most of the DC protection circuits are unidirectional TVS tubes, the AC protection circuits are mostly bidirectional TVS tubes, the multi-channel protection circuits are TVS array devices, and the high-power protection circuits are special protection modules.

8) In the process of using TVS tube, considering the dispersion of TVS, try to reduce the number of serial / parallel.

Sixth Part:  What is TVS diode typical application 

TVS diodes have the advantages of extremely fast response speed, low clamping voltage, precise voltage, etc., so they are used in the field where the protection device is required to be relatively high. Automotive electronics, home, industrial control, lighting, communication, medical and other industries, such as DC power line, RS485 interface, communication power, I / O port, etc.

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