Capacitor

Basic Electronics Part 1 – Passive Components

A capacitor is a passive electronic component which can store electrical charges. It consists of two (2) conducting plates and separated by an insulating material. This insulating material is also called the dielectric material. The capacitor’s basic function is to concentrate the electric field of voltage applied across the dielectric so that it can store and accumulate charge coming from the voltage source. Then the stored energy can be discharged by the dielectric when the charging source is replaced by a conducting path.

Because of this characteristic, the capacitor continuously charges and discharges when AC (Alternating Current) voltage is applied to it. While on the other hand, when DC (Direct Current) voltage is applied to it, the capacitor acts as an open circuit which charges completely and never discharges unless the DC voltage source is replaced by a load (a conducting path or a circuit). The current along a capacitor in a circuit is equal to zero.

The unit of capacitance is Farad (F) but one Farad (1 F) is too much for circuit applications. Because of this commercially available capacitors come in microfarads (μF or picofarads (pF).

Voltage Rating

Capacitors have corresponding voltage ratings that specify the maximum voltage that can be applied across the plates without destroying the dielectric. A voltage rating higher than the actual potential difference applied across the capacitor is recommended for safety purposes when creating circuits or electronics applications.

Polarized and Non-polarized Capacitors

Capacitors can be categorized as either a polarized capacitor or a non-polarized capacitor. A polarized capacitor is a type of capacitor that requires polarity when connected in a circuit. Its two leads cannot be interchange and can only be connected one way in a circuit. The positive lead is usually longer than the negative lead. In some capacitors, a stripe in the casing tells where the negative lead is. A non-polarized capacitor is a type of capacitor that can be connected with its two terminals in either position. Ceramic, mica, and mylar capacitors are examples of this.

Types of Capacitors

Capacitors come in different packages to suit different applications.

Electrolytic Capacitors - Made of electrolyte, electrolytic capacitors are the most common type of polarized capacitor. It is commonly used for Ripple filtes, and timing circuits. Although not very accurate and suitable for high frequency circuits, electrolytic capacitors are cheap and are readily available in very small or very large values in μF.

Ceramic Capacitors - Constructed with materials such as titanium acid barium for the dielectric. Internally these capacitors are not constructed as a coil, so they are well suited for use in high frequency applications. Typically used to by-pass high frequency signals to ground. They are shaped like a disk, available in very small capacitance values and very small sizes. The most commonly used type of non-polarized capacitor. Like the electrolytic, it is cheap and easily available.

Tantalum Capacitors - Made of Tantalum Pentoxide. They are electrolytic capacitors but used with a material called tantalum for the electrodes. It is superior to electrolytic capacitors having excellent temperature ranges and frequency characteristics. Tantalum capacitors are expensive and easily damaged by spikes in the circuit.

Super Capacitors - The Electric Double Layer capacitor is called a super capacitor because of its capacitance value that is 0.47 Farad (470,000 µF). Despite the large capacitance value, its physical dimensions are relatively small. It has a diameter of 21 mm and a height of 11 mm. Like electrolytic caps the super capacitor is a type of polarized capacitor.

Polypropylene Capacitors - The polypropylene film is the dielectric used in this type of capacitor. Can be used in applications within a frequency range of 100KHz. Polypropylene caps has a tolerance of about 1% and are available in very small values.

Polyester Film Capacitors - This capacitor uses a thin polyester film as a dielectric. Polyester film caps are cheap and are stable with temperature changes. They are also readily available and are widely used. Tolerance is approximately 5% to 10%.

Polystyrene Capacitors – Uses Polystyrene as the dielectric. This type of capacitors are often used in filter circuits or timing applications and are not suited for high frequency circuits.

Metalized Polyester Film Capacitors - Dielectric made of metalized Polyester or "Mylar". These capacitors are stable with temperature change and can come in very small physical sizes.

Epoxy Capacitors - Created using an epoxy dipped polymers as a protective coating. Epoxy capacitors are widely available, stable, and cheap. Can be quite large depending on capacity or rated voltage and so may not be suitable for all applications.

Mica Capacitors – Uses Mica as the dielectric. Often used in creating resonance circuits, frequency filters, and military devices. This type of capacitor is highly stable and very durable making it expensive.

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