Almost every designer knows about metal oxide varistors (MOVs). These bidirectional and non-linear surge suppressor devices are ubiquitous in a large variety of applications to limit voltage during a surge or transient event. But how do you choose the best MOV for your design from the multiple form factors and various surge protection ranges?
Bourns has just developed a new white paper entitled ‘Tips on Selecting the Right MOV Surge Suppressor’. In it, the company provides a step-by-step selection approach as well as detailed information on the features and specifications to help you narrow down your search. Below is a quick summary of the key steps:
1. Determine the application’s surge requirement. For instance, a good rule of thumb for selecting an MOV is for the Inom to be typically half of its Imax rating.
2. Determine the operating voltage and the application’s maximum peak voltage.
3. Determine if there are any special requirements such as operating temperature.
4. Consider the highest clamping voltage (Vc) the protected equipment can tolerate.
Other useful information in determining the right MOV is that designers can put MOVs in parallel to decrease the clamping voltage. While this does increase the surge rating, it is not always double the individual MOV rating. That’s because the two MOVs do not share the surge current equally. A good tip is to start with the 60/40 rule, which means that the first MOV that reacts to a surge probably needs to handle 60 percent of the total surge. A good alternative to putting MOVs in parallel is to use an MLV (multi-layer varistor). MLVs are constructed of many layers of MOVs stacked on top of one another and inherently provide matched voltage.
Also, it is beneficial to know that manufacturers can rate their MOVs either AC, DC, and/or Maximum Continuous Operating, and list their clamping voltage at 1 mA DC based on regulatory standards such as IEC 61643-331.
With one of the industry’s most comprehensive lines of MOVs, Bourns has everything from space-saving SMT to high-energy disc and harsh environment AEC-Q200 compliant devices. It also has customised MOV capabilities.
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