How Transient Voltage Suppressor Diodes Protect Your Electronics

Understanding Transient Voltage Suppressor DIODES

Diodes are the most fundamental semiconductor devices and are commonly used in many circuit designs, such as rectifiers, converters, inverters, protection circuits, and voltage regulators. There is a special type of diode called the TVS diode (Transient Voltage Suppressor), which plays a crucial role in handling transient spikes in power electronic circuit designs. Here, we will delve deeper into transient voltage suppressor diodes.

What is a Transient?

A transient is a short-duration spike in voltage or current that can damage circuits in various ways. Some transient events occur only once, while others may be repetitive, and these spikes can range from a few millivolts to several kilovolts, with durations from nanoseconds to hundreds of milliseconds.

What Causes Transients in Electronic Circuits?

Transients can be caused by internal or external connections within a circuit. Internally, transients may be generated due to inductive load switching or contact failures in switches and connectors. Externally, they may be caused by lightning strikes or inductive switching.

Transient Voltage Suppressor Devices (TVS)

A transient voltage suppressor, or TVS, is a protective device used to protect circuits from the effects of transient spikes in voltage or current. The primary method of protecting circuits from electrical overstress is to connect these TVS devices in parallel with the circuit.

A transient voltage suppressor diode is a solid-state PN junction diode specifically designed to eliminate the effects of sudden or transient overvoltages on sensitive semiconductors and circuits. The transient voltage suppressor diode is a clamping device, so whenever the induced voltage exceeds the avalanche breakdown voltage, it absorbs the excess energy from the overvoltage event and then automatically resets after the overvoltage condition has passed. Indeed, standard diodes and Zener diodes can also be used for overvoltage/transient protection, but they are not as robust as transient voltage suppressor diodes because standard and Zener diodes are designed for rectification and voltage regulation.

Why Transient Voltage Suppressor Diodes is essential for us

TVS Diodes in 12V DC Power Line Protection for Automotive Applications

The working environment of automobiles is extremely harsh. Electronic control units, infotainment systems, sensors, and other automotive electronic devices are all connected to a single power line, which is supplied by the engine and battery. Since the engine and battery are susceptible to fluctuations due to temperature, operating conditions, and other factors, the power supply can be quite unstable. Additionally, automotive systems that use electromagnetic coil loads, such as fuel injection systems, valves, motors, and electrical and water control systems, can introduce ESD (Electrostatic Discharge), spike noise, and other types of transients and surge voltages into the power and signal lines.

For primary protection of automotive power lines against load dump, the SM8S series of TVS diodes can be divided into two categories: epitaxial and non-epitaxial. In reverse-biased mode, they exhibit similar breakdown characteristics. However, epitaxial TVS diodes have a low forward voltage drop in forward mode, while non-epitaxial TVS diodes have a relatively higher forward voltage drop under the same conditions. This characteristic is particularly important for reverse voltage applied to the power line. In reverse power input mode, the power line voltage is the same as the forward voltage drop of the TVS diode, which can easily cause electronic circuit failures. In this case, the low forward voltage drop of the epitaxial TVS diode can effectively solve this problem.

TVS Diodes in RS-485 Interface Protection Applications

In the field of communication applications, the highly stable and reliable RS-485 has become one of the most commonly used interface standards in industrial environments worldwide. RS-485 is a data transmission bus specification, and its transceivers are the devices that implement this bus specification. Due to the asymmetric operating voltage of RS-485 transceivers (ranging from -7V to 12V), these devices are extremely susceptible to threats from ESD (Electrostatic Discharge), EFT (Electrical Fast Transient), and lightning-induced surges.

Compared to other solutions in the industry, the SM712 TVS diode is the preferred choice for protection. The SM712 has a power handling capability that is 50% higher than other solutions, providing electronic engineers with more flexibility to meet regulatory standards worldwide. The SM712 TVS diode can safely absorb repetitive ESD discharges at the highest levels specified by the IEC61000-4-2 international standard without degradation in performance. It can also safely dissipate surge currents of up to 19A at very low clamping voltages. Additionally, the SM712 complies with the AEC-Q101 standard, ensuring automotive-grade quality and the highest reliability in harsh industrial environments, giving electronic engineers peace of mind.

TVS Diodes in I/O Interface Protection Applications

I/O interfaces are extremely widely used across various industries. I/O interfaces serve as the medium and bridge for information exchange between the CPU and I/O devices. The connection and data exchange between the CPU and external devices, as well as memory, are both facilitated through interface devices. The former is referred to as the I/O interface, while the latter is known as the memory interface. Memory typically operates under the synchronous control of the CPU, resulting in relatively simple interface circuits. In contrast, I/O devices come in a wide variety, each with its own unique interface circuit. I/O interfaces are highly susceptible to external factors and are prone to overvoltage events. Therefore, it is necessary to use circuit protection devices to protect them from damage caused by overvoltage, thereby enhancing reliability.

Types of Transient Voltage Suppressor Diodes

Transient Voltage Suppressor (TVS) Diodes are mainly categorized into the following types:

1.Unidirectional TVS Diode

The structure of a unidirectional TVS diode is similar to that of a conventional diode, consisting of a single PN junction. Under normal voltage conditions, it remains in a reverse-biased cut-off state with almost no current flow through it. When a positive transient event

2.Bidirectional TVS Diode

A bidirectional TVS diode is equivalent to two unidirectional TVS diodes connected in antiparallel. It can rapidly conduct and clamp the voltage regardless of whether the transient overvoltage in the circuit is positive or negative voltages, as long as the voltage exceeds its breakdown voltage. For instance, in communication lines, signal transmission may be subject to transient overvoltage interference from different directions, and a bidirectional TVS diode can provide effective protection against both positive and negative voltages.

3.Surface-Mount TVS Diode

Structure and Principle: The surface-mount TVS diode is packaged using surface-mount technology (SMT). Its leads are short and flat against the chip surface. Its principle is consistent with other types of TVS diodes. However, this package form reduces the size of the diode, increases production efficiency, and improves the space utilization of the PCB. In compact electronic devices, surface-mount TVS diodes save a significant amount of space. Additionally, with short leads, they have low parasitic inductance, making them suitable for high-frequency circuit applications.

Surface-Mount TVS Diodes for applications: Widely used in consumer electronics, such as smartphones and smartwatches. These devices have very limited internal space and strict size requirements for electronic components. Surface-mount TVS diodes can meet these needs and provide reliable protection for various chips and circuits inside. In high-density circuit designs, they can also improve the integration and reliability of the circuit.

How TVS Diodes work

Basic Working Principle: TVS diodes are essentially a special type of diode. Under normal voltage conditions, the TVS diode is in a reverse-biased cut-off state, with extremely high internal resistance and only a tiny leakage current flow through it. This has almost no effect on the normal operation of the circuit boards, acting like an open circuit. However, when a transient event occurs in the circuit and the voltage amplitude exceeds the breakdown voltage of the TVS diode, the Transient Voltage Suppressor diode will respond quickly. Its PN junction will undergo avalanche breakdown (for avalanche diodes) or Zener breakdown (for Zener voltage-type TVS diodes), thus entering a low-impedance conducting state. At this point, the TVS diode can limit the overvoltage to a specific voltage level, known as the clamping voltage, by conducting. This prevents excess current from being applied to other sensitive components connected in parallel, thereby protecting the circuit components from damage.

Avalanche Breakdown Principle (Avalanche-Type TVS Diode): When the reverse voltage reaches a certain level, the charge carriers (electrons and holes) in the semiconductor gain sufficient energy. As these carriers move, they collide with lattice atoms, generating new electron-hole pairs. The newly generated carriers continue to collide with other atoms, causing the number of carriers to increase rapidly, like an avalanche diodes, forming a large reverse current. Avalanche-type Transient Voltage Suppressor diodes utilize this avalanche breakdown effect to quickly conduct and generate a large current when a sudden overvoltage occurs, limiting the voltage to the clamping voltage level and thus protecting the circuit. Since avalanche breakdown can handle a large transient power, avalanche-type TVS diodes are suitable for applications that require withstanding high-energy transient impacts, such as industrial control electronic equipment and automotive electronic systems.

Zener Breakdown Principle (Zener-Type TVS Diode): Zener diodes are typically used in low-voltage, high-precision protection applications. In a highly doped PN junction, when the reverse voltage reaches a certain value, the internal electric field strength is sufficient to directly pull electrons out of covalent bonds, forming electron-hole pairs and generating reverse breakdown current. This is known as Zener breakdown. Zener diodes use the Zener breakdown principle to quickly clamp the voltage to a relatively stable level when an overvoltage occurs. They have a small leakage current and can provide transient protection for circuits with high voltage precision requirements. They are commonly used in circuits with high precision requirements, such as the power supply pins of microprocessors.

How to Select a Transient Voltage Suppressor (TVS) Diode?

There are many types of TVS diodes available on the market, each designed for specific applications. When selecting a TVS diode, you can refer to the following parameters:

1.Reverse Standoff Voltage: The reverse standoff voltage is the maximum voltage that can be applied to the protector without actually activating the device. The device's V_R should be equal to or higher than the peak operating voltage of the circuit being protected. This ensures that the overvoltage protection device does not clamp normal circuit operation or signal voltages. 

2.Breakdown Voltage: The breakdown voltage is the voltage at which the diode begins to protect and conduct transient current. Typically, V_BR is specified at 1mA.

3.Clamping Voltage: The clamping voltage is the highest voltage that the protected circuit will experience during a test waveform event. In most datasheets, the clamping voltage is given for a 1A or 2A waveform with an 8µS rise time.

4.Peak Pulse Current (IPP): The peak current is the maximum current that the protection device can withstand.

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