Contents
What is a Metal Oxide Varistor?
Simply put, a metal oxide varistor is a variable resistor. However, unlike potentiometers, a metal oxide varistor can vary its resistance in electronic devices depending on how much voltage you apply.
If the transient voltage applied increases, then the resistance will decrease. This aspect is highly beneficial as surge protection is often implemented to protect electrical networks.
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Metal Oxide Varistor Construction
A metal oxide varistor is a voltage-dependent resistor. A metallic oxide varistor is around 90% Zinc oxide and 10% other metallic oxides. Typical metal oxide varistors are made with ceramic powers, such as zinc oxide grains.
The metal oxide varistors
Metal Oxide Varistor Features
The Metal Oxide Varistor features include:
- Insulation resistance is 1000 Mohn
- DC voltage ranges from 175V to 1200V
- AC voltage goes from 130V to 1000V
- Operating temperates between -55 and +85°C
Metal Oxide Varistor Protection Circuit – Design Tips
Let’s look at how you can use a metal oxide varistor to protect circuits in the event of voltage spikes. Here are some design tips for designing a course that offers complete protection.
- Firstly, when selecting a metal oxide varistor, you must determine the continuous working voltage. You can opt for a varistor with a higher operating voltage to achieve the lowest possible leakage current. Choosing a varistor with a 10-15% higher maximum rated voltage for circuit protection technologies is common.
- Next, you need to select a varistor that has the power to dissipate more energy that is more than the energy required dissipation throughout a surge shift. You calculate by the maximum load of the varistor throughout a surge, factoring in the environment and the specifications.
- Next, factor in the surge or peak transient current through your varistor and choose a varistor with an actual surge rating slightly higher than the current rating needed by an event.
- It would help if you chose a model that offers the necessary clamping voltage. You can select the clamping voltage based on the approximate max voltage value you want to allow the circuit’s output or input to appear during an event.
metal oxide varistors
How to use a Metal Oxide Varistor in your circuit
Varistors frequently get used within electronic circuits in parallel with a course that you need to protect.
When the voltage is within your rated limit, the varistor resistance will be high, and the current follows through the circuit and not through the varistor.
However, when a voltage spike happens, it will appear across the varistor parallel to your AC mains. The high voltage decreases the resistance value of your varistor, and it will appear similar to a short.
This action causes a large current to flow through your varistor, which could disconnect the circuit or blow a fuse. When voltage spikes occur, the faulted high voltage will go back to normal quickly. The duration of the current flow won’t be high enough to cause a fuse to blow, and then the circuit goes back to normal.
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Summary
Now, you have all the information you need about choosing the right varistors to handle any surge current.
Handling voltage ratings is essential to ensure electronic components remain operational and do not get damaged. Excessive voltage can be very detrimental, but the maximum voltage will no longer be an issue if you manage peak voltage with a varistor.
Don’t hesitate to contact us if you have any questions.
