TVS Overview
TVS (Transient Voltage Suppressor) is a transient voltage suppressor. Transient voltage refers to a transient distortion of current and voltage, characterized by ultra-high voltage, transient, and high frequency. Transient voltage is generally caused by static electricity and lightning, and the release of static electricity will generate a very high transient voltage, and the speed is very fast. If this high voltage cannot be instantly conducted away, the circuit system will be severely damaged. TVS is a solid-state component that can absorb transient high energy and protect the system from static electricity and lightning damage.

Working process: When the two poles are subjected to a reverse transient high-energy impact, the TVS diode can convert the high impedance between the two poles into low impedance at a speed of ps to absorb the instantaneous high current and clamp the voltage between the two poles at a predetermined value, effectively protecting the precision components in the electronic circuit. After the instantaneous pulse ends, the TVS diode automatically returns to the reverse cutoff state, allowing the entire circuit to enter normal voltage.

Basic characteristics: TVS is a special type of voltage regulator diode, whose electrical characteristics are determined by device structure, doping concentration, substrate resistivity, etc. The surge power and surge current capacity are proportional to the junction area. According to power, it can be divided into levels of 24W, 40W, 400W, 600W, 1500W, and 5000W. If converted into avalanche energy with a period of 1ms, they are 0.033, 0.055, 0.55, 0.8, 2.1, and 7.0 joules, respectively.

Characteristics of TVS tube

1) Low voltage, low capacitance

2) High transient power

3) Clamping voltage is easy to control

4) Small deviation in breakdown voltage

5) Low leakage current

6) Fast response speed (ns level)

7) Small size, easy to install

8) No damage limit, high reliability

parameter description

Breakdown voltage VBR

The voltage measured at both ends of the TVS device in the area where breakdown occurs under the specified test current IT is called the breakdown voltage.

Maximum reverse pulse peak current IPP

The peak pulse current that TVS can withstand is usually tested under a time condition of 10/1000us.

Maximum reverse operating voltage VRMM

During the TVS protection circuit process, the voltage value at both ends of the TVS under the specified reverse current is called the maximum reverse operating voltage VRMM. Generally, VRMM=(0.8~0.9) V (BR). When using, the VRMM should not be lower than the normal operating voltage of the protected circuit or device.

Maximum clamping voltage VC

The maximum voltage value at both ends of the device under the action of pulse peak current IPP is called the maximum clamping voltage. When in use, VC (max) should not exceed the maximum allowable safe voltage of the protected device. The ratio of the maximum clamping voltage to the breakdown voltage is called the clamping coefficient (usually ranging from 1.2 to 1.4). When in use, the VC should not exceed the maximum voltage that the protected circuit can withstand.

Reverse pulse peak power PPP

Pulse peak power PPP refers to the product of the pulse peak current IPP of 10/1000 μ s wave and the maximum clamping voltage VC, i.e. PPP=IPP * VC; At a given maximum clamping voltage, the larger the power consumption PPP, the greater its ability to withstand surge currents. At a given power consumption PPP, the lower the clamping voltage, the stronger its ability to withstand surge currents; In addition, it is also related to the pulse waveform, pulse time, and ambient temperature.

Capacitor CJ

The capacitance of TVS is determined by the area of the silicon wafer and the bias voltage. In the case of zero bias, the capacitance value decreases with the increase of the bias voltage. The size of the capacitor can affect the response time of TVS devices. For high-frequency circuits, capacitors are generally chosen to be as small as possible (such as TV, FM, BT, GPS, TVS capacitors should not exceed 3pF), while for circuits with low capacitance requirements, capacitors can be chosen to be higher than 40pF.

The normal operating voltage of the protected circuit is less than VRMM, VBR, VC, and the maximum voltage that the protected circuit can withstand

Unidirectional TVS and bidirectional TVS:

1) The forward characteristics of unidirectional TVS are the same as those of ordinary voltage regulators, and the reverse breakdown inflection point is approximately a "right angle" for hard breakdown, making it a typical PN junction avalanche device. The curve segment from the breakdown point to the VC value indicates that when there is an instantaneous overvoltage pulse, the current of the device increases sharply while the reverse voltage rises to the clamping voltage value and remains basically unchanged.

2) Bidirectional TVS can discharge surge pulses at both ends of the line, thereby protecting the system from ESD damage.

3) Bidirectional TVS is suitable for AC circuits, while unidirectional TVS is generally used for DC circuits.

The difference between TVS tube and other devices

1. Principle of voltage regulator diode

Zener diode (also known as Zener diode) is a semiconductor device that has high resistance until the critical reverse breakdown voltage. At this critical breakdown point, the reverse resistance decreases to a very small value, and in this low resistance region, the current increases while the voltage remains constant. Zener diodes are classified based on their breakdown voltage, and because of this characteristic, Zener diodes are mainly used as voltage regulators or voltage reference components. Zener diodes can be connected in series for use at higher voltages, and more stable voltage can be obtained through series connection.

2. The difference between TVS tube and voltage regulator diode

Both can be used for voltage stabilization and operate in reverse cutoff state, with forward characteristics similar to ordinary diodes and reverse characteristics typical of PN junction avalanche devices. However, the breakdown current of TVS tubes is smaller, with only 1mA exceeding 10V. In comparison, the breakdown current of voltage regulator diodes is much larger, but the voltage regulation accuracy of voltage regulator diodes can be relatively high. Moreover, TVS tubes emphasize transient response, which means that the response time of the voltage regulator diode is usually slower than that of TVS tubes. At the same time, the power of TVS tube is relatively high, while the power of voltage regulator tube is relatively low.

3. The difference between TVS and ceramic capacitors

Ceramic capacitors can be used for ESD protection, which is not only cheap but also easy to design, but these devices have relatively weak resistance to high voltage. A 5kV impact can cause about 10% of ceramic capacitors to fail, and the damage rate reaches 60% at 10kV, while TVS can withstand a voltage of 15kV.

4. The difference between TVS and MLV

Multilayer metal oxide structure devices (MLVs) can also effectively suppress transient high voltage surges, but their functionality will degrade under transient voltage surges. When transient voltage invades, the leakage current and termination voltage values will deviate from their original parameters and become inaccurate. In addition, its impedance is relatively high, so the suppression voltage can reach 2-3 times the termination voltage. TVS diodes have lower suppression voltage and lower capacitance.

Application of TVS

1) Various power systems

2) Household appliances

3) Industrial control circuits and instruments

4) Communication equipment

5) Computer and network equipment system