This product highlight features varistors and discusses the differences between single layer and multilayer technology varistors. The two technologies complement each other nicely to cover a wide variety of applications. Each technology has strengths and weaknesses which are important to understand for proper selection during the design process. This product highlight will discuss the technologies briefly and explain the benefits and typical applications for each.
Single Layer Varistors
Single layer varistors and multilayer varistors both use zinc oxide crystal grains as their base material. Standard single layer disc and high energy varistors are produced by dry powder pressing technology. As the name indicates, there is only one, relatively thick, monolithic layer between the external electrodes. This feature allows single layer varistors to withstand much higher surge currents and can dissipate more energy compared to multilayer varistors. Typically rated peak single currents for high energy ZOV varistor series achieve values of up to 80KA and can dissipate around 4KJ of energy without failure. Since the voltage rating is directly proportional to the thickness of single layer varistors it is difficult to produce single layer varistors for very low rated voltages as thin disks are very fragile and can break easily. For low voltage applications, Stackpole recommends multilayer varistors.
Single layer varistor applications include protection for communications and network equipment, white goods, lighting ballasts, motor protection and controls, surge protected outlets, distribution panels, phone line protection, power supplies, and elevators / escalator motors and controls.
Stackpole's single layer varistor series include ZOV, SV, CV, CVH, PV and DV series. Among these series ZOV features larger disk sizes with rigid standard or custom design terminals. The CV, CVH, and SV series are radial through-hole components and are the most widely used varistor type. The PV and DV series are surface mount components that utilize 5mm or 7mm varistor disks; therefore they are direct SMD alternatives to CV and CVH radial through-hole varistors of that size. PV series are plastic encapsulated varistors. The DV series have no encapsulation and are the smallest SMD single layer varistors available.
ZOV (radial leaded): VAC = 60 to 680V, Ipk = 15KA to 80KA, Wmax = 90 to 4140J.
CV / CVH / SV (radial leaded): VAC = 50 to 680V, Ipk = 100 to 6500A, Wmax = 0.6 to 620J.
PV / DV (SMD): VAC = 11 to 300V, Ipk = 100 to 1200A, Wmax = 0.6 to 30J.
Multilayer components are produced by tape casting technology. Multilayer varistors (MLV) consist of layers that are stacked together with intermediate metal electrodes printed onto the zinc oxide varistor tape. Tape casting technology is the optimal method to produce large area and thin varistor ceramics, which is impossible by dry pressing technology. This technology produces SMD varistors for rated voltage down to 2 Vrms. Multilayer varistors provide more efficient energy dispersion through the component meaning longer varistor lifetime compared to single layer varistors.
In addition, the max current capability and the capacitance can be adjusted by changing the number of layers in the multilayer structure. Multilayer varistors are limited in their energy handling capability due to their small size and mass. For high energy applications, single layer varistors are recommended.Â Fortunately, lower voltage applications normally served by multilayer varistors typically have lower energy handling requirements.
Such applications include protection for a wide variety of portable electronics devices, I/O ports and interfaces, controllers and instrumentation, IC and transistor protection, relays, sensors, audio, and keyboards / keypad protection.
Stackpole offers several different multilayer series to serve a variety of low to medium voltage application requirements. The surface mount ZV series and the leaded ZVL are typically applied to protect circuit board level products and offer the broadest range of sizes and voltages. For applications where extremely low varistor capacitance is required, such as when there is high frequency of data transfer, ZVX series offers appropriate protection. ZVE series of varistors is specifically designed for the protection of integrated circuits and other components at the circuit board level from ESD damage.
ZVL(radial leaded): VAC = 2V to 40V, Ipk = 100A to 2000A, Wmax = 0.1J to 33.4J
ZV (SMD): VAC = 2V to 95V, Ipk = 120A to 1200A, Wmax = 0.2J to 12.2J
ZVX(SMD): VAC = 2V to 30V, Ipk = 40A, Wmax = 0.1J
ZVE(SMD): VAC = 14V, Ipk = 2A, Wmax = 0.1J
Automotive Grade Varistors and Dual Function Components
AV and AVL varistors are developed for automotive applications and have voltage ratings designed for use in 12, 24, and 42V systems. They are characterized for load dump energy and performance at twice the typical battery voltage to ensure reliable voltage protection long term. Almost all electronic systems in an automobile like anti-lock brake system, direct ignition system, airbag control system, wiper & seat manipulation motors can be damaged by destructive voltage surges. Varistor technology is typically the protection device of choice. DC motors used in automotive applications for wipers, side window and seat motion are source of electromagnetic interference (EMI). To suppress EMI, a capacitor is needed. Stackpole has a special dual function component comprised of a varistor and a capacitor in a single component. The MV and OV series are dual function components ideal for the applications with DC motors. Below is a summary of the rms voltage, peak current, and energy handling for the two technologies.
For more information about Stackpole products, contact Stackpole Electronics, Inc. at
Stackpole Electronics, Inc.
2700 Wycliff Road Suite 410,
Raleigh NC 27607
Stackpole Electronics Inc. is a leading global manufacturer of resistors supplying to the worlds largest OEMs, contract manufacturers and distributors. Headquartered in Raleigh, N.C., the privately held company began manufacturing in 1928 as part of Stackpole Carbon Company in St. Mary's, Pennsylvania. Now part of the Akahane Stackpole Manufacturing Group (ASMG), Stackpole has manufacturing facilities in Japan, Taiwan, China and Mexico; warehousing facilities in El Paso, Shenzhen and Japan; and international sales offices in Tokyo, Taipei, London, Hong Kong and Shenzhen.