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Capacitor basics

capacitor symbols

capacitor stores electric charge. It blocks DC and allows AC to pass through. In simplest form, capacitor is made of two metal plates separated by insulator called as dielectric. There are two types based on the value i.e. fixed capacitor and variable capacitor. Further based on polarity there are two types i.e. polarized and non-polarized capacitors.

Capacitance is measured in farads(F). To simply values there are microfarad, nanofarad and picofarad units. Capacitor is choosen based on factors such as working voltage, leakage current, value, tolerance, type and stability.

Capacitor stores charge when voltage is applied across it. Its value Q depends on V and C.
Q = V * C

Energy (W) stored in a capacitor in Joules = 1/2( Q*V)

Capacitors in series

capacitors in series

As shown in the figure, if two capacitors are connected in series, following can be derived.
•  Total capacitance is as per equation below.
•  Total capacitance is as per equation below.
1/C = 1/C1 + 1/C2
Capacitors in series, total capacitance, C= C1*C2/C1+C2

Capacitors in parallel

capacitors in parallel

As shown in the figure, if two capacitors are connected in parallel, following can be derived.
•  Total capacitance is as per equation below.
•  Their voltages are same across but charges are different.
Capacitors in parallel, total capacitance C= C1+C2

Capacitor Impedance

Capacitor reactance Xc = 1/(2*pi*f*C)
Where, C is in farads, f is in Hz. As in resistor, parameters oppose to current flow is referred as resistance, in capacitor parameter opposed to a.c. is referred as capacitive reactance.
Capacitive reactance will be translated to a negative imaginary impedance i.e. impedance at -90 degrees.
capacitor impedance = 0-i*Xc

Capacitor Types

There are various types of fixed capacitors which include polyester, Mica, Ceramic, Electrolytic etc. These capacitors will have single fixed value and are used for various applications.

Polyester capacitors are made using two strips of polyester film wound between two strips of aluminium foil. Two leads are attached with these foils for providing connectivity with other electronic circuit components or mounting the capacitors on the PCB.

Mica capacitor is made of mica material naturally available. They are used in RF tuned circuits where low loss is needed. They have very low tolerance but have higher stability and working voltage.

Ceramic capacitors are of various types and will have value from 10 pF to 1 µF. They are available in different sizes such as rod, disc and plate shaped. They are used in applications not requiring exact value of capacitance.

Electrolytic capacitors will have polarity and hence need to be connected taking into consideration their polarity as current flows from positive(+) terminal.

Capacitor manufacturers

The popular capacitor manufacturers are murata, CTR, Electronic concepts, vishay, DEC, CDE etc.

Vishay

Vishay manufacture capacitors of various types viz. solid and wet tantalum capacitors, multilayer chip and disk type ceramic capacitors, aluminum, wet tantalum capacitors, conformal coated capacitors, molded tantalum surface mount capacitors etc.

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