TVS diodes are often used to protect transmission lines, data lines, or line overvoltages caused by lightning strikes, inductive load switches, and ESD. Do you really know about TVS diodes, or do you know little about them? What are the differences between TVS and other diode technologies such as silicon protection arrays and diode arrays? If you have been following the TVS selection guide, then you should take a look at this blog post.

TVS diode introduction

The TVS diode is a protective element specifically designed to protect electronic circuits from transient voltage spikes. They provide a fast and reliable overvoltage protection solution in circuits, especially in power, data and signal lines, to prevent voltage surges due to lightning strikes, switching operations, electrostatic discharge (ESD) or other electromagnetic interference (EMI).

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Working principle

The operating principle of TVS diodes is based on their unique reverse breakdown characteristics. Under normal working conditions, the TVS diode presents a high impedance state, which almost does not affect the normal operation of the circuit. However, when the voltage at both ends of the circuit exceeds the breakdown voltage of the TVS diode, the TVS diode will quickly change from a high-impedance state to a low-impedance state, allowing a large amount of current to pass through itself, thus clamping the voltage at a pre-set level. This process takes place at the nanosecond or even picosecond level, ensuring a fast response and effectively protecting the sensitive electronic components at the back end.

type

TVS diodes can be divided into one-way and two-way two kinds:

• Unidirectional TVS: Usually used in DC circuits, they are only activated when the reverse voltage exceeds a threshold.

• Two-way TVS: Suitable for AC circuits because they provide protection against both forward and reverse voltage spikes.

peculiarity

• Fast response time: TVS diodes can respond to voltage changes in nanoseconds or even picoseconds, quickly clamping the voltage to a safe level.

• Bidirectional and unidirectional types: TVS diodes are available in unidirectional and bidirectional types to protect against forward and reverse voltage surges, respectively.

• Clamp voltage: This is the maximum voltage at which the TVS diode starts to switch on and limits the voltage rise.

• Peak pulse power dissipation capacity: The instantaneous high energy pulse power that TVS diodes can withstand.

• Low leakage current: Under normal operating voltage, TVS diodes have a very low leakage current and consume almost no energy in the circuit.

• Wide operating temperature range: TVS diodes usually have a wide operating temperature range and are suitable for various environmental conditions.

• Repeatability: TVS diodes can experience transient events multiple times without significantly affecting their performance.

• Various packaging forms: In order to adapt to different application needs, TVS diodes have a variety of packaging forms, including SMD (surface mount) and lead lines.

Apply

• Power supply

• Data and communication interfaces (e.g. USB, HDMI, RS-232, etc.)

• Automotive electronic system

• Household appliance

• Computers and peripherals

• Telecommunications and network equipment

encapsulation

TVS diodes are available in a variety of package forms, including axial lead, radial lead, SMD (surface mount) and more miniaturized chipscale packages to accommodate different board designs and space constraints.

TVS diode selection

The maximum clamping voltage VC is less than the maximum safety voltage allowed by the circuit; The cut-off voltage VRWM is greater than the maximum working voltage of the circuit, and VRWM can generally be selected to be equal to or slightly greater than the maximum normal working voltage of the circuit; The rated maximum pulse power (given in TVS parameters) PM should be greater than the maximum transient surge power; TVS tube is generally in parallel on the protected circuit when used; In order to limit the current flowing through the TVS tube to not exceed the peak current IPP allowed through the tube, current-limiting elements should be added in series in the line, such as resistors, self-restoring fuses, inductors, etc.

The steps to select TVS are as follows:

Determine the DC voltage or continuous operating voltage of the circuit to be protected. -- > The reverse displacement voltage of TVS is the operating voltage (VRWM) -- The VRWM of the TVS selected is equal to or greater than the operating voltage specified in step 1 above. This ensures that the current absorbed by TVS under normal working conditions is negligible. If the voltage specified in step 1 is higher than the VRWM of TVS, TVS will absorb a large amount of leakage current and be in the state of avalanche breakdown, thus affecting the operation of the circuit. -- > Maximum peak pulse power: Determine the interference pulse of the circuit, according to the waveform of the interference pulse, pulse duration, determine the peak pulse power of TVS that can effectively suppress the interference. -- > The maximum clamp voltage (VC) of the selected TVS should be lower than the maximum voltage allowed by the protected circuit. - > Unipolar or bipolar - There is often a misconception that bidirectional TVS is used to suppress reverse surge pulses, but this is not the case. Bidirectional TVS is used for alternating current or from positive and negative bidirectional pulses. TVS is also sometimes used to reduce capacitance. If the circuit only has a forward level signal, then a one-way TVS is sufficient. The TVS operation mode is as follows: when the surge is forward, the TVS is in the reverse avalanche breakdown state; In the case of reverse surge, the TVS conducts and absorbs the surge energy like a forward-biased diode. This is not the case in low-capacitance circuits. Two-way TVS should be selected to protect the low capacitor components in the circuit from damage caused by reverse surges. If you know the more accurate surge current IPP, then you can use VC to determine its power, if you can not determine the approximate range of power, generally speaking, it is better to choose a larger power.

① Determine the maximum DC operating voltage or continuous operating voltage of the protected circuit, the rated standard voltage of the circuit and the "high-end" tolerance;
②TVS rated reverse shutdown voltage VFM should be greater than or equal to the maximum operating voltage of the protected circuit. If the selected VFM is too low, the device may enter the avalanche or affect the normal operation of the circuit because the reverse leakage current is too large. TVS series connection can increase the total fixed reverse turn-off voltage of TVS;
(3) The maximum clamping voltage VC of TVS should be less than the damage voltage of the protected circuit;
④ In the specified pulse duration, the maximum peak pulse power consumption of TVS PM must be greater than the peak pulse power that may occur in the protected circuit. After the maximum clamping voltage is determined, the peak pulse current should be greater than the transient surge current.
⑤ For the protection of data interface circuits, attention must also be paid to the selection of TVS devices with appropriate junction capacitance Cj;
⑥ According to the use of TVS polarity and packaging structure. It is reasonable to choose bipolar TVS for AC circuit. TVS array is more advantageous for multi-wire protection.
⑦ Temperature consideration. Transient voltage suppressor TVS can operate between -55 ° C and +150 ° C. If TVS is required to work in a changing temperature environment, because its reverse leakage current ID increases with the increase of working temperature, power consumption decreases with the increase of TVS junction temperature, so the effect of temperature change on its working characteristics must be considered when using.

Comparison of the structure of TVS diode with Schottky diode and Zener diode

Device structure comparison: Schottky diode is composed of metal semiconductor structure. It carries charge through a plurality of carriers and is responsive to processing with low current leakage and forward bias voltage (VF). Schottky diodes are mainly used in high frequency circuits.

Zener diode is composed of heavily doped P-N semiconductor structure. There are two kinds of physical effects that can be called Zener states (Zener effect and avalanche effect). The Zener effect occurs when a low reverse voltage is applied to both ends of the P-N junction due to quantum effects. The avalanche effect occurs when the electron hole pair collides with the lattice when a reverse voltage of more than 5.5 volts is applied to both ends of the PN junction. Zener diodes based on Zener effect are widely used as voltage reference sources in circuits.

The TVS diode consists of a P-N semiconductor structure designed for overvoltage protection. P-N junctions are usually coated to protect premature voltage arcs in non-conducting states. When a transient voltage event occurs, the TVS diode is switched on by avalanche effect to clamp down on the transient voltage. TVS diodes are widely used as overvoltage circuit protection devices in the telecommunications, general electronics and digital consumer product markets to protect them from lightning, ESD and other transient voltages.

SPA stands for Silicon Protection Arrays. It is an array that integrates PN junction, SCR or other silicon protection structures in a multi-pin structure. SPA can be used as an integrated solution for ESD, lightning and EFT protection in the telecommunications, general electronics and digital consumer product markets with multiple protection opportunities. For example, it can be used for HDMI, USB, and Ethernet port ESD protection.