What is a Variable Capacitor – Construction, Types and Applications

Generally, a capacitor is a two-terminal component where the two conducting surfaces are parallel to each other. The terminals of a capacitor will be separated by a non-conducting material which is known as a dielectric and these are connected to a voltage source. The main function of the capacitor is to store electrical energy, which is known as capacitance. The unit of this is the farad (F). The capacitance of a capacitor can be increased by a non-conducting material. Once the capacitor is charged through a voltage source, then one plate of the capacitor will be charged positively whereas the second plate will negatively be charged. Basically it is like a battery but whenever the plates of the capacitor are touched, the electrical energy which is stored will be dissipated immediately, whereas, in a battery, the energy will be dissipated gradually. This article discusses an overview of a variable capacitor.

What is a Variable Capacitor?

Definition: Whenever the capacitance of a capacitor is changed based on the necessity to a certain range of values is known as a variable capacitor. The two plates of this capacitor can be made with metals where one plate is fixed & the other one is movable. The range of capacitance that is provided by the capacitor can range from 10 pF to 500 picofarads. The symbol of this capacitor is shown below where the arrow symbol in the image shows that is a variable one.

Construction of Variable Capacitor

The construction of the variable capacitor is shown below. These capacitors are frequently used in different applications due to their simple construction. Generally, these capacitors are made with 2 sets of hemispherical metal plates which are divided through air gaps. One set of the metal plates is fixed whereas the other one is connected to a shaft so that the user can allow turning the assembly, thus the capacitance can be changed when it is needed. So the construction of each type of capacitor varies based on its type.

The designing of this capacitor can be done based on the working principle of a normal capacitor. The conductive plates of this capacitor are arranged in parallel and that are divided with dielectric coatings composed with different materials like reinforced paper, mica otherwise certain kinds of ceramics. Not like typically fixed capacitors, these capacitors are designed to change levels of capacitance. In most of the cases, the variable capacitance can be achieved by changing the distance among the parallel plates within a capacitor.

Types of Variable Capacitors

There are two types of variable capacitors available in the markets which include the following. The capacitance of the following capacitors can be changed manually by using screwdrivers otherwise any devices.

• Tuning Capacitors
• Trimmer Capacitors
• Mechanical Capacitors
• Electronic Capacitors

Tuning Capacitors

The designing of tuning capacitors can be done using a frame. This frame includes a stator as well as a rotor. The capacitor’s frame can give support to the material mica as well as stator. When the stator is inactive, then the rotors start rotating with the help of a shaft.

When the movable rotor plates enter into the immobile stator, then the capacitance value can be considered as maximum otherwise minimum. The capacitance values range can be provided from these capacitors which range from picofarads to tens of picofarads.

These capacitors are used in the receivers of radio which have LC circuits. An alternate name of these capacitors is tuning condensers.

Trimmer Capacitors

Trimmer capacitor is also known as variable capacitors & provides the basic calibration of apparatus while manufacturing otherwise servicing. These capacitors are frequently arranged on the printed circuit board so that the user doesn’t have the right of entry to change them. Because of this, these capacitors are not expensive.

These capacitors are used to set the values of oscillator frequency, rise, latencies, & fall times within a circuit. These capacitors allow servicemen to adjust devices when it is required. These types of capacitors are classified into two types namely air trimmer & ceramic trimmer.

This capacitor includes three leads where one lead is linked to the immobile part; the second lead is linked to the rotary and the last lead is common. The movement of this capacitor can be observed with the help of the semi-circle shaped movable disc. This capacitor includes two plates and these plates are arranged in parallel to each other by separating with a dielectric material.

The classification of these capacitors can be done based on the dielectric material used like air trimmer & ceramic trimmer.

Mechanical Capacitors

These capacitors have a set of curved plates which are connected to a knob. The main benefit of this is, the capacitance of the capacitor can be altered easily if required. These are reliable when they are mechanical because they are not overly complicated.

Electronic Capacitors

The capacitance of these capacitors can be changed by applying DC voltage to them. The applications of these capacitors mainly include multi-meters, resistance, and amperage. Here the DC (direct current) is the kind of current supplied from a battery.

Applications

The applications of the variable capacitor include the following.

• Trimmer capacitors are used where a capacitance value is needed to be matched to a particular circuit in the manufacturing process.
• The main reason to use this capacitor is, the components used in the circuit have own tolerances. So the tolerance values can be changed by 20%
• from what the designer expected to notice in a circuit. So these capacitors are used to adapt these tolerances.
• These are frequently used in numerous circuits through the microwave.
• These capacitors are applicable in medical instruments like NMR scanners, MRI to generate extremely high magnetic fields.
• The common applications are tuners, oscillators, filters, and crystal oscillators.
• These capacitors can be found in communication devices like mobile radios, transmitters & receivers in aerospace, CATV amplifiers & signal splitters.

FAQs

1). What is the main function of the variable capacitor?

It is used to fix the resonant frequency in the LC circuit.

2). How these capacitors are made?

These are made with two sets of curved metal plates and they are divided by air gaps

3). What is a ganged capacitor?

The combination of two capacitors that are connected together is known as a ganged capacitor.

4). What are the two types of variable capacitors?

They are tuning capacitors and trimming capacitors.

5). What is the capacitance values of a variable capacitor?

Typically ranges from 100pF to 500pF

Thus, this is all about variable capacitors and the characteristics of the variable capacitor mainly include accuracy, tolerance, polarity, voltage rating, and capacitance range. Here is a question for you, what are the advantages of a variable capacitor?