What is the symbol for varistor?
Varistor symbol The varistor circuit symbol can be seen to be very similar to that of a thermistor. It consists of the basic resistor symbol of a rectangle with a diagonal line through it that has a small added section parallel to the body of the resistor symbol. This indicates the no-linear nature of the varistor.
How do you read a varistor?
Touch one meter probe to the free varistor lead and the other probe to the connected lead. Read the resistance on the meter. If it reads nearly infinite resistance, the varistor is still good. If it reads very low resistance, the varistor is blown.
What is the function of varistor?
Varistors are used to protect a circuit from high voltage surges. When a high voltage surge is applied to a circuit, the outcome is usually catastrophic to the circuit. A capacitor may be installed across the signal lines. However, this capacitor cannot suppress voltage surges.
How do I select a MOV varistor?
The first step of choosing a MOV is determining the continuous working voltage that will be provided across the varistor, you have to choose the varistor with maximum AC or DC voltage that matches or slightly higher than the applied voltage.
What is the clamping voltage of a varistor?
This rated or clamping voltage is the voltage across the varistor measured with the specified DC current of 1mA. That is, the DC voltage level applied across its terminals that allows a current of 1mA to flow through the varistors resistive body which itself is dependant upon the materials used in its construction.
How do you choose varistor voltage?
For example, selecting a MOV or silicon varistor for that matter, for voltage, its maximum continuous rms voltage rating should be just above the highest expected supply voltage, say 130 volts rms for a 120 volt supply, and 260 volts rms for a 230 volt supply.
How do I read a MOV rating?
The current rating of the MOV could be twice that of the SMPS rating, meaning if the SMPS wattage is rated at 24 watts at the secondary, then the primary could be calculated as 24/285 = 0.084 amps, therefore the MOV current could be anywhere above 0.084 x 2 = 0.168 amps or 200mA.
What leads to variable resistance in varistors?
The resistance of a varistor is variable and depends on the voltage applied. The word is composed of parts of the words “variable resistor. Their resistance decreases when the voltage increases. In case of excessive voltage increases, their resistance drops dramatically.