When inspecting the AC input side of a power supply circuit, you may notice the presence of a small, orange or blue-colored component that is circular. This part is known as a metal-oxide varistor (MOV), that of which is the most common varistor found in circuit assemblies. Varistors are used for protection against excessive transient voltages or for achieving optimal operating conditions, and the metal-oxide varistor is one that can adjust its resistance in accordance with the voltage applied across. Metal-oxide varistors are typically used together with fuses for the protection of circuits against voltage spikes. To help you better understand such components and find the right fit for your needs, we will discuss metal oxide varistors and their design in more detail.
MOVs are often compared to potentiometers for their variability in resistance, though the two are set apart in the fact that a MOV has a resistance based on the applied voltage. As voltage increases across the MOV, the overall resistance of the component will drop. The opposite is true for decreases in voltage, resulting in a resistance increase. With the basic set of operating conditions, MOVs can serve as a useful surge protector.
During standard operating conditions, the resistance of the MOV is quite high. As such, little voltage is drawn from the circuit by the MOV. When a voltage spike occurs, the spike will be directed through the MOV as long as it is situated parallel to the AC mains. This causes the resistance of the MOV to plummet, and the diode junction will break down and cause a large current flow. Through the dissipation of the surge through the MOV, the rest of the surrounding equipment can be protected against damage.
While a MOV can protect equipment from voltage spikes, they are not able to handle prolonged surges. With repeated surges, the MOV will begin to break down over time and lose certain properties. Each surge will also lower the clamping voltage of the component, eventually leading to a breakdown. As such, MOVs are commonly placed together with fuses or circuit breakers so that protection can be guaranteed in the instance of a part failure. To avoid such issues, any AC metal-oxide varistor that has been in operation for some time should be inspected, maintained, or replaced as necessary.
When you are in the market for a metal-oxide varistor that can serve your needs, there are a few factors that are important to consider. For instance, the maximum working voltage is the DC steady-state voltage, while the clamping voltage is the value at which the surge current will be dissipated by the MOV. Surge current values are also important as they determine the peak current the device can handle before becoming damaged. Alongside such characteristics, it may also be useful to base your decision on response times, energy absorption rates, and leakage current values of various options. Once you have narrowed down the specific requirements you have for a metal-oxide varistor, look no further than Internet for Aviation to fulfill all your operational needs.
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