Eliminating noise interference and preventing surge hazards has always been a headache for electronic device designers. Transient voltage suppressor (TVS: transientvoltagesuppressor) can easily solve these problems.

When TVS is subjected to reverse high energy impact at the north and south poles, it can change the impedance between the north and south poles from high to low at a speed of 10-12s, absorb up to several kilowatts of surge power, so that the potential clamp between the north and south poles is located at a predetermined value, and effectively maintain the equipment in the electronic equipment from the harm of surge pulses. TVS has the advantages of fast response time, large transient power, low leakage current, small breakdown voltage error, easy control of clamp voltage, small size, and has been widely used in household appliances, electronic instruments, communication equipment, power supplies, computer systems and other fields.

Features and important parameters of 1TVS

Figure 1TVS voltage-current characteristics

11TVS features

The circuit symbol of TVS is the same as that of the general voltage regulator. The voltage-current characteristic curve is shown in Figure 1.

Its forward characteristics are the same as those of ordinary diodes, and its reverse characteristics are typical of pN junction avalanche equipment. Figure 2 shows the current-hour and voltage-hour curves of TVS. Under the use of surge voltage, the voltage between the north and south poles of TVS rises from the rated reverse turn-off voltage VWM to the breakdown voltage Vbr, and is broken down. With the breakdown current present, the current flowing through the TVS will reach the peak pulse current Ipp, while the voltage at both ends is clamped below the predetermined maximum clamping voltage VC. Subsequently, with the exponential attenuation of the pulse current, the voltage between the north and south poles of TVS also continues to decline, and finally recovers to the initial state, which is the process of TVS suppressing the possible surge pulse power and maintaining the electronic element equipment.

12TVS important parameters

(1) Maximum reverse leakage current ID and rated reverse turn-off voltage VWM

VWM is the most continuous DC or pulse voltage of TVS. When this reverse voltage is applied to the north and south poles of TVS, it is in the reverse off state, and the current flowing through it should be less than or equal to its maximum reverse leakage current ID.

(2) Minimum breakdown voltage Vbr and breakdown current IR

Vbr is the minimum breakdown voltage of TVS. At 25℃, TVS below this voltage will not produce avalanches. When TVS flows through the regular 1mA current (IR), the voltage applied to the north and south poles of TVS is its minimum breakdown voltage Vbr. According to the dispersion degree of TVS Vbr and standard value, Vbr can be divided into 5% and 10%. For 5% Vbr, VWM=0.85Vbr; For 10% Vbr, VWM=0.81Vbr.

Figure 2TVS voltage (current) time characteristics

(3) The most clamped voltage VC and the most peak pulse current Ipp When the pulse peak current Ipp with a continuous time of 20μs flows through TVS, the most peak voltage presented at both ends is VC. VC and Ipp reflect the surge suppression ability of TVS. The ratio of VC to Vbr is called the clamping factor and is generally between 1.2 and 1.4.

（4) Electrical capacity C

The capacitance C is determined by the avalanche junction section of TVS and is measured at a specific frequency of 1MHz. The size of C is proportional to the current acceptance capacity of TVS, and too much C will cause signal attenuation. Therefore, C is an important parameter for TVS in data interface circuits.

(5) Maximum peak pulse power consumption pM

pM is the maximum peak pulse power dissipation that TVS can accept. Under the given maximum clamping voltage, the higher the power consumption pM, the greater the acceptance capacity of the surge current. Under a given power consumption pM, the lower the clamping voltage VC, the greater the acceptance capacity of the surge current. In addition, the peak pulse power consumption is also related to pulse waveform, continuation time and ambient temperature. In addition, the transient pulse that TVS can accept is not repeated, and the regular pulse repetition frequency (the ratio of continuous time to intermittent time) of the device is 0 01%. If repeated pulses are present in the circuit, the accumulation of pulse power should be considered, which may damage the TVS.