Detailed analysis and research on the characteristics and applications of TVS devices

In view of the analysis of the characteristics and main parameters of TVS devices along with their working principles, this paper presents that TVS can effectively protect TN power systems, DC power supplies, signal lines, and transistor integrated circuits. It has a wide range of applications and is known for its safety and reliability. A typical protection circuit design using TVS devices in various electronic systems is also discussed. When implementing TVS protection, it is essential to select appropriate components based on the specific protection requirements and the relevant parameters of the circuit. Power frequency overvoltage, resonant overvoltage, and transient overvoltage in the power grid—such as operating overvoltage and lightning-induced overvoltage—can introduce dangerous surge energy into the internal circuits of electrical equipment. This may disrupt normal operations or even cause damage to the circuitry. Additionally, digital integrated circuits are vulnerable to surges like ESD (electrostatic discharge) and EFT (electric fast transient burst), which may lead to malfunctions, system crashes, or permanent damage. By employing TVS devices, the circuit can be finely protected, ensuring that sensitive components remain safe from various surge pulses. This study is significant for a detailed understanding and research into the characteristics and practical applications of TVS technology. ### 1. Structure and Classification of TVS The TVS (Transient Voltage Suppressor) is a new type of high-performance protection device, based on a Zener diode structure. It typically uses a diode-type axial lead package. The core component is a semiconductor chip made from silicon wafers or thin films. The chip can have either unipolar or bipolar structures. Unipolar TVS features a single PN junction, while bipolar TVS includes two PN junctions. These junctions are exposed through glass purification and then encapsulated in modified epoxy resin. TVS devices come in unipolar and bipolar types. Unipolar TVS protects against surges in one direction, while bipolar TVS provides protection against surges in both directions, effectively functioning like two Zener diodes connected in reverse. Bipolar TVS offers advantages such as low junction capacitance, fast response time, and high power handling capability. Unipolar TVS is commonly used in DC and fixed-direction signal circuits, whereas bipolar TVS is more suitable for AC and variable signal circuits. TVS arrays are often used for multi-line protection. In some cases, TVS can be connected in series with a diode to reduce parasitic capacitance, making it ideal for high-speed signal ports. The serial/parallel configuration should be carefully controlled during application. Environmental factors such as temperature changes must also be considered, as they affect the performance of TVS, particularly increasing reverse leakage current when temperatures rise. TVS devices are available in various power ratings, including 500 W, 1000 W, 1500 W, and 5000 W. ### 2. Main Parameters and Selection of TVS #### 2.1 Minimum Breakdown Voltage (VBR) The minimum breakdown voltage (VBR) is the voltage across the TVS when a specified test current passes through it. VBR is categorized into two types: VBR (5%) and VBR (10%), depending on the tolerance level. #### 2.2 Rated Reverse Working Voltage (VWM) VWM is the voltage applied to the TVS under reverse operation when the reverse current (IR) is at a specified level. Generally, VWM is approximately 0.8–0.9 times VBR. For 5% tolerance devices, VWM = 0.85 × VBR, and for 10% tolerance devices, VWM = 0.81 × VBR. It is important to choose a VWM value that is greater than or equal to the maximum continuous operating voltage (US) of the circuit, and close to it for optimal protection. #### 2.3 Maximum Reverse Pulse Peak Current (IPP) IPP is the maximum peak current the TVS can handle under specified pulse conditions. It must be greater than the expected transient surge current in the circuit. #### 2.4 Maximum Clamping Voltage (VC) VC is the maximum voltage across the TVS when the peak current IPP flows through it. It represents the protection level of the TVS and should be less than the withstand voltage (UW) of the protected circuit. The clamping factor is VC / VBR, typically ranging from 1.2 to 1.4. #### 2.5 Peak Pulse Power (Ppp) Ppp is calculated as the product of IPP and VC. It depends on the pulse waveform, duration, and ambient temperature. In practice, a 20% safety margin should be considered when selecting Ppp. The rated pulse power (Pppm) must exceed the expected transient power in the circuit. Repeated pulse energy accumulation must also be accounted for in the design. #### 2.6 Capacitance (C) Capacitance of a TVS is influenced by the size of the chip and the bias voltage. Higher bias voltages result in lower capacitance. Choosing the right capacitance is crucial to avoid signal distortion or interference. #### 2.7 Reverse Leakage Current (ID) ID is the current flowing through the TVS when the rated reverse voltage (VWM) is applied. It should be less than or equal to the maximum allowable leakage current. #### 2.8 Clamp Response Time (TC) TC refers to the time it takes for the TVS to clamp the voltage from zero to the breakdown voltage. TVS has an extremely fast response time, typically less than 1 ps. ### 3. Analysis of TVS Characteristics #### 3.1 Volt-Ampere Characteristics of TVS TVS protects the circuit by clamping the voltage. When the TVS is reverse-biased and within the 0–VBR range, it remains in a high-resistance state. Once the reverse voltage exceeds VBR, the current increases rapidly, and the TVS enters a low-resistance conduction mode. The transition occurs in picoseconds, and the voltage is clamped below VC. After the surge, the TVS returns to a high-impedance state. #### 3.2 Clamping Characteristics of TVS As a voltage-limiting device, TVS clamps overvoltages and limits them within a safe range to protect downstream circuits. Using the loop voltage method, the output voltage can be calculated. For example, if the surge voltage is 8 kV, and Rg = 330 Ω, RS = 0.14 Ω, and VBR = 6 V, the current i ≈ 24 A, and the output voltage is about 10 V. This reduces the hazardous surge voltage to a safe level. However, the condition Rg > RS + RLoad must be satisfied. ### 4. TVS Application #### 4.1 TVS in TN Power Systems Lightning surges and switching transients can enter electrical equipment via power lines, causing damage. To prevent this, a two-stage protection system using MOV and TVS is implemented. MOV acts as the first stage, absorbing part of the surge, while TVS serves as the second stage, further reducing the overvoltage. The line between points AB should be at least 5 m long to ensure proper coordination between the two stages. #### 4.2 TVS in Network Signal Lines TVS can also be used for signal line protection. Combining GDT and TVS in a signal protector ensures fast response and minimal leakage, providing reliable protection for high-speed networks. #### 4.3 TVS in DC Power Systems A common PC power supply circuit includes a transformer, rectifier, and DC output. Installing a bidirectional TVS at the transformer output absorbs impulse currents and clamps the voltage. A unidirectional TVS at the DC output protects the load from overvoltage surges. #### 4.4 TVS in Transistor Circuits Transistors are key components in integrated circuits. Adding TVS at input and output terminals protects against ESD/EFT surges, preventing damage to the circuit. #### 4.5 TVS in TTL Logic Circuits TTL circuits, composed of transistors, are protected by adding TVS at input, output, and power supply terminals to prevent damage from transient overvoltages. #### 4.6 TVS in MOS Integrated Circuits MOS transistors, used in CMOS circuits, are protected by TVS at input, output, and power supply terminals, ensuring reliable operation under transient voltage conditions. ### 5. Conclusion (1) TVS offers advantages such as fast response, high power, low inter-electrode capacitance, small size, no leakage current, and broad applicability. It can effectively protect TN power systems, DC power supplies, signal lines, and transistor integrated circuits from various surges, including ESD/EFT. (2) Circuit design must consider the characteristics of the protected circuit, environmental conditions, and TVS parameters such as VC, IPP, VWM, VBR, and Ppp. The TVS circuit should not interfere with normal operation and must safely discharge expected surges, clamping dangerous voltages within the circuit's safe range.

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