Varistor Schematic Symbol

Varistor symbol The symbol of a varistor circuit is very similar to that of a thermistor. It consists of a 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 which indicates the nonlinear nature of the varistor.

What is varistor used for?

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 read varistor code?

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.

Is varistor a diode?

A varistor is an electronic component with an electrical resistance that varies with the applied voltage. Also known as a voltage-dependent resistor (VDR), it has a nonlinear, non-ohmic current–voltage characteristic that is similar to that of a diode.

Is varistor a resistor?

A varistor is a voltage dependent resistor (VDR). 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.

Does varistor have polarity?

Varistor (Variable resistor) is a nonlinear resistive element of the voltage dependence that resistance changes with applied voltage. Varistor is equivalent with Zener diode of two series connection. Therefore, do not have polarity.

What happens when a varistor fails?

Under different current conditions, failure modes include electrical puncture (see Figure 4), physical cracking (see Figure 5), and thermal runaway. Cracking happens because varistors are basically a ceramic material, and hitting them with a sharp high-amplitude surge is like hitting a dinner plate with a hammer.

Is a varistor a fuse?

Unlike the fuse or circuit breaker which offers over-current protection, the varistor provides over-voltage protection by means of voltage-clamping in a similar way to the zener diode.

Can you remove a varistor?

Just leave it open. Simply remove it untill you find a replacement. The circuit will work without it.

Do varistors fail open or short?

Varistors short circuit when an overage in potential is applied to it.

What is the difference between diode and varistor?

As the illustration below shows, chip varistors have a laminated structure, with breakdown voltage and capacitance being controlled by the number of layers and the interlayer design. TVS diodes on the other hand are a combination of P-type and N-type semiconductors. They are silicon-based ESD protection components.

Is varistor a semiconductor?

Varistors are nonlinear two-element semiconductors that drop in resistance as voltage increases. Voltage dependent resistors are often used as surge suppressors for sensitive circuits.

What is the working principle of varistor?

A varistor does not obey Ohm's law and hence it is not like an ohmic resistor. It is basically a non-ohmic resistor that does not follow Ohm's law and hence it is also called a non-linear resistor or a voltage-dependent resistor.

Is varistor a thermistor?

What is the difference between a varistor and a thermistor? One is voltage sensitive the other temperature sensitive. A varistor is resistor that changes resistance with applied voltage. A thermistor is one that changes value with temperature.

What is the breakdown voltage of varistor?

The breakdown field of commercial ZnO varistor ceramics is commonly 200–300 V/mm and the nonlinear coefficient is ∼50.

Is a varistor directional?

Modern varistors are primarily based on sintered ceramic metal oxide materials which exhibit directional behavior only on a microscopic scale. Varistors are used as control or compensation elements in circuits either to provide optimal operating conditions or to protect against excessive transient voltages.

Are all varistors the same?

Depending upon applications, varistors are classified as high voltage and low voltage varistors. High voltage varistors are used in transmission lines and transformers. Low voltage varistors on the other hand are used in electrical and electronic devices.

What causes MOV to fail?

How does an MOV fail? A. When subjected to stresses above its ratings, an MOV can fail as a short circuit. If applied conditions significantly exceed the energy rating of the device, and current is not limited, the MOV may be completely destroyed.

Do varistors get hot?

Excessive idle current during normal, steady-state operation will cause heating in the varistor. Because the varistor has a negative temperature coefficient, the current will increase as the varistor becomes hotter.

Where do you put the varistor?

4) Circuit position: Varistor is generally used between the L line and N line of the input end of the product, which is between the fuse and thermistor; 5) Residual voltage: The residual voltage of the varistor (ie the maximum limit voltage) will be directly applied to the back-end circuit of the product.