What is IsoMOV™ Technology? Highly reliable protection achieved by combining MOV and GDT

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Overvoltage protection, which determines the reliability of electronic devices, poses challenges when using conventional metal oxide varistors (MOVs) alone, such as increased leakage current and thermal runaway over long-term use.

Bourns' IsoMOV™ technology, developed with a hybrid structure that combines MOVs and GDTs (Gas Discharge Tubes), solves these issues and provides highly reliable, long-life overvoltage protection. This article will introduce the technical features and operating principles of IsoMOV™, as well as its advantages and benefits through actual application examples.

What is IsoMOV™ Technology?

Figure 1: IsoMOV™ configuration diagram *Provided by Borns

IsoMOV™ technology is a hybrid overvoltage protection element developed by Bourns that combines MOV and GDT to overcome issues of long-term reliability and thermal runaway that are difficult to address with conventional protection elements.

MOVs are commonly used for overvoltage protection on AC lines, but over long periods of use, their leakage current increases, posing a risk of failure due to the accompanying thermal runaway.In contrast, with IsoMOV™, the GDT acts to block the leakage current of the MOV, reducing the electrical stress on the MOV and preventing element degradation.

As shown in Figure 1, IsoMOV™ integrates an MOV and a GDT, incorporating glass sealing, spacers, passivation layers, etc. This enables highly reliable overvoltage protection that maximizes the performance of the MOV and GDT while minimizing the effects of external environments.

Furthermore, as shown in Figure 2, in conventional MOV elements (left), current passing through the grain boundaries becomes leakage current, causing degradation over long-term use. The diagram in the center shows the structure of IsoMOV™, which combines MOV and GDT to suppress MOV degradation and improve reliability. The right side of Figure 2 shows the appearance of an actual IsoMOV™ product, whose compact housing contributes to space-saving designs.

In this way, IsoMOV™ utilizes a hybrid structure that takes advantage of the properties of MOVs and GDTs to provide a long-life, high-performance protection solution, providing stable operation even in harsh environments such as automotive and industrial equipment.

Figure 2: Comparison of MOV element and IsoMOV™ structures (Left: Internal structure of MOV element, Center: Diagram of IsoMOV™ structure, Right: Actual photo of IsoMOV™ product) — Figure 2: Comparison of MOV element and IsoMOV™ structures (Left: Internal structure of MOV element, Center: Structural diagram of IsoMOV™, Right: Actual photo of IsoMOV™ product) *Provided by Borns

Technical Advantages of IsoMOV™ Technology

IsoMOV™ technology utilizes a hybrid structure in which MOVs and GDTs complement each other, achieving high reliability and performance not found in conventional protection devices. The main technological advantages are as follows:

1. Achieving high reliability through mutual complementarity

In IsoMOV™ technology, the MOV and GDT have a symbiotic relationship that enhances each other's reliability. This is based on the same design concept as Bourns' previously offered GMOV™ Hybrid Protector. The GDT blocks the MOV's leakage current, suppressing MOV degradation. Conversely, the MOV prevents the GDT's follow-on current, preventing damage to the GDT. This mutual complementarity prevents thermal runaway even when surges are repeatedly applied, maintaining stable protection performance over the long term.

2. Improved performance due to unique MOV shape

The MOV element used in IsoMOV™ technology has a unique structural design that differs from conventional designs. This allows surge energy to be distributed more evenly within the element. As a result, even when surges are repeatedly applied, localized stress concentrations are reduced and the MOV element's deterioration over time is gradual. This improves performance stability over long periods of use, enabling reliable protection.

In addition, the energy distribution inside the IsoMOV™ protector is optimized, increasing the surge withstand capacity per unit area, meaning it can withstand greater surge energy compared to MOVs of the same size.

This performance improvement can be quantified by comparing the surge ratings of IsoMOV™ technology with the best performing MOVs, as shown in the table below.

*IsoMOV™ protectors have surge ratings equivalent to larger MOV protectors

Product dimensions (diameter)	MOV (highest performance product)	IsoMOV™ Hybrid Protector
10mm	2000	3000
14mm	3000	5000
20mm	5000	8000

Table 1: Comparison of surge ratings of IsoMOV™ technology and MOVs (unit: V)

3. Supports a wide range of operating voltages and temperatures

IsoMOV™ technology is designed to operate stably in harsh environments, particularly in high voltage and high temperature environments up to 550VAC and 125°C, which are difficult for conventional MOVs to withstand.

This wide range of operating conditions enables IsoMOV™ technology to be used as a reliable protection element in applications requiring high durability, such as industrial equipment, automotive equipment, and power equipment. This increased design flexibility allows engineers to create circuit protection solutions for a wider range of applications.

4. TOV (short-term overvoltage) resistance and fast response

IsoMOV™ technology provides high immunity to Temporary Overvoltage (TOV), eliminating the excessive design margin required with conventional MOVs alone, enabling more efficient and compact circuit designs and increasing design freedom.

Furthermore, IsoMOV™ technology provides fast and stable clamping during surges. As shown in Figure 3, it starts operating quickly with a lower clamping voltage compared to standard MOVs for 8/20µs surge currents, minimizing overvoltage stress on the device.

These characteristics allow IsoMOV™ technology to maintain high reliability even against repeated surges and temporary overvoltages, providing long-lasting and consistent protection.

Figure 3: Comparison of voltage and current waveforms when a surge is applied *Provided by Borns — Figure 3: Comparison of voltage and current waveforms when a surge is applied

5. Reliability guaranteed by international standard certification

IsoMOV™ technology is a product that complies with international safety standards and has the following certifications:

・IEC61051-2: Certified to comply with international standards for overvoltage protection devices
- UL1449 Edition 5: Certified as a Type 4 Component and Type 5 Component under the US surge protection standard

These certifications provide third-party assurance of the performance and safety of IsoMOV™ technology, allowing it to be used with confidence in equipment designs that require compliance. Type 4 Component is for embedded use within a system, while Type 5 Component is for more limited use, increasing design flexibility.

Intended use environment for IsoMOV™ technology

■ Expected design conditions
・Circuits that require overvoltage protection (voltage clamp) on AC/DC lines
- AC line with low EMI emissions (due to lower capacitance than standard MOVs)
・When you want to secure a margin for TOV (Temporary Over Voltage) while maintaining the accuracy of the clamp voltage

■Design benefits
-High reliability (meets lifespan requirements of 5 years or more)
・Space saving (one part replaces the functions of two parts)
Higher surge voltage rating compared to standard MOVs

■ Example of simplified circuit configuration
The diagram below shows the difference between a conventional MOV + auxiliary element configuration and a configuration using IsoMOV™ technology.
IsoMOV™ technology allows multiple protection elements to be integrated into one, reducing component count and simplifying design.

Figure 4: Example of simplified circuit configuration (Left: conventional configuration, Right: IsoMOV™ technology configuration) *Provided by Borns

IsoMOV™ Technology Application Examples

IsoMOV™ technology is a protection element that simultaneously achieves high reliability, space-saving design, and high surge resistance in a variety of devices that require overvoltage protection. Below are some typical examples of its use in actual applications.

AC/DC module (in battery energy storage system)

■ Challenges
・Overvoltage protection
-Protection against Category IV impulses for more than 20 years
- Highly reliable and compact protection solution

■ Effects of implementation
-Extend the life of the product
(Long lifespan due to no degradation caused by leakage current when using MOV alone)
・High performance, small protection element reduces the cost of protection functions

AC power supply (in the network switch)

■ Challenges
- Surge resistance needs to be increased to 6kV in a smaller space
・Highly reliable and compact protection solution required

■ Effects of implementation
Highly reliable surge protection
- Small size and high integration of MOV and GDT make PCB design easy
- Suitable for strengthening surge resistance to 6kA

Single-phase smart grid meter

■ Challenges
- Highest performance overvoltage protection can be implemented in limited board space
- New methods are needed to replace the combination of MOV and GDT.

■ Effects of implementation
- Space saving, high reliability, improved surge rating
・ISOM3 is much more compact than a combination of MOV and GDT

EV charging station

■ Challenges
・10kA 8/20us surge resistance required
- Highly reliable and compact protection solution

■ Effects of implementation
- Smaller size, higher performance protection solution
- Suitable for strengthening surge resistance to 10kA

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