Capacitors

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Capacitors

Basics

You can think of a capacitor as sort of a rechargeable battery, connect it to a voltage and a current will flow into it charging it up, later it will have a voltage of its own that can push the current back out. The key equation for a capacitor is:

Where:

• C = capacitance ( units: farad = volts /coulomb )
• V = voltage ( unit: volts )
• Q = charge in the capacitor ( unit: coulomb )

A simple application of the formula above occurs when a constant or near constant current flow into a capacitor: then the voltage across it increases at a constant rate, the graph of the voltage against time will be a line rising ( or falling for a negative current ) from the left to the right. If the current is constant the line is straight.

Another way of thinking of a capacitor ( which is only partly correct ) is that it is a resistor with infinite resistance for DC and lower and lower resistance as the frequency goes up. This is a fair model for sinusoidal voltages and currents, but is less useful for signals such as square waves.

Uses:

• ac coupling –- blocking -- isolation
• timing
• Time for a capacitor to charge or discharge is very roughly RC where R is the resistor in series with the capacitor.
• Filter ( often power supply filter )
• decoupling
• tuned circuits

All capacitors are formed by having 2 conductors ( or plates ) connected to the two terminals of the capacitor. The conductors are separated from each other by insulator, typically very thin. Adding charge to one side forces like charge off the opposite plate because like charges repel. The larger the plates and the closer together they are the less voltage it takes to force in the charge. If the insulator ( called the dielectric ) is too thin it will be pierced by the charge and the capacitors becomes a conductor. Typically the basic specifications for a capacitors are its capacitance and the maximum voltage that can be used without causing the dialectic to break down.
There are many diferent technologies for manufacturing capacitor each with its own advantages and disadvantages.

External Links

1. Capacitor From Wikipedia, the free encyclopedia
2. RC circuit From Wikipedia, the free encyclopedia
3. RC Timers and Timing Circuits
4. Decoupling capacitor From Wikipedia, the free encyclopedia
5. Components: Capacitors
6. Electronics and radio components See the section called Capacitors

Electrolytic

In electrolytic capacitors the insulating layer is formed by electro chemical action between the plates and other chemicals in the capacitor. This forms a very thin layer which allows large capacitance in a small package. Typically this works for one polarity and not another so electrolytic capacitors are marked with their polarity. There are some non-polarized electrolytics, but they are not common.

Some electrolytic capacitors manufactured between 1999 until today are made with bad electrolyte. Avoid these, see capacitor plague for more info.

Aluminum

• Aluminium Electrolytic capacitors

Tantalum

• 10uF Tantalum Capacitor

Ceramic

• Ceramic capacitors Ceramic capacitors - an overview, information or tutorial about the basics of the ceramic capacitor: its construction, technical information, properties and the uses of the ceramic capacitor.

Film

Polycarbonate

• Polycarbonate capacitors Polycarbonate capacitors - an overview, tutorial about the basics of the polycarbonate capacitor or polycarbonate film capacitor: its construction, properties and general data and information.

Exotics

Mica

• Silver Mica Capacitor Silver Mica Capacitor - an overview or tutorial about the basics of the silver mica capacitor, its construction, properties and the uses of silver mica capacitors particularly in RF circuits.