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Capacitors
- 2. A basiccapacitor has two parallel plates separated by an insulating material A capacitor stores an electrical charge between the two plates The unit of capacitance is Farads (F) Capacitance values are normally smaller, such as µF, nF or pF In a way, a capacitor is a little like a battery. Although they work in completely different ways, capacitors and batteries both store electrical energy Inside the capacitor, the terminals connect to two metal plates separated by a non-conducting substance, or dielectric. You can easily make a capacitor from two pieces of aluminum foil and a piece of paper. It won't be a particularly good capacitor in terms of its storage capacity, but it will work.
- 3. Basic capacitorconstruction Dielectric material Plate 1 Plate 2 The dielectric material is an insulator therefore no current flows through the capacitor
- 4. Storing a chargebetween the plates Electrons on the left plate are attracted toward the positive terminal of the voltage source This leaves an excess of positively charged holes The electrons are pushed toward the right plate Excess electrons leave a negative charge + - + _ + _
- 5. The dielectricmaterial determines the type of capacitor Fixed Capacitors ◦ Nonpolarized May be connected into circuit with either terminal of capacitor connected to the high voltage side of the circuit. Insulator: Paper, Mica, Ceramic, Polymer ◦ Electrolytic The negative terminal must always be at a lower voltage than the positive terminal Plates or Electrodes: Aluminum, Tantalum
- 6. Difficult tomake nonpolarized capacitors that store a large amount of charge or operate at high voltages. ◦ Tolerance on capacitance values is very large +50%/-25% is not unusual http://www.marvac.com/fun/ceramic_capacitor_codes.a spx PSpice Symbol
- 8. Some capacitorsare polarised, they can only be connected one way around Electrolytic capacitors are polarised
- 9. Variable capacitorsare used in communication equipment, radios, televisions and VCRs They can be adjusted by consumers by tuning controls Trimmers are internal adjusted capacitors that a consumer cannot adjust
- 10. These variable capacitorswould be difficult to squeeze into your mobile phone and iPod Current technology uses semi-conductor variable capacitors called varactors (varicaps)
- 11. The capacitancein a varactor is created when a purpose diode is reversed biased Adjusting the reverse bias alters the capacitance value A simple radio receiver using varactor http://www.microst.it
- 12. The ceramiccapacitor is a type of capacitor that is used in many applications from audio to RF.. Ceramic capacitor types are by far the most commonly used type of capacitor being cheap and reliable and their loss factor is particularly low although this is dependent on the exact dielectric in use. Range Values range from a few picofarads to around 820 microfarads. Uses In view of their constructional properties, these capacitors are widely used both in leaded and surface mount formats
- 13. Electrolytic capacitor: Electrolytic capacitors area type of capacitor that is polarised. they have a frequency limit if around 100 kHz. Range They are able to offer high capacitance values - typically above 1μF Uses are most widely used for low frequency applications - power supplies, decoupling and audio coupling applications.
- 14. Electrolytic capacitornames after using oxide film formed electrochemically on electrode surface as dielectric. Aluminum (Al), tantalum (Ta), niobium (Nb), titanium (Ti), zirconium (Zr), hafnium (Hf) and other metals can form a fine, highly isolative oxide currently ,the only two metals in practical application are aluminum and tantalum. Oxide film formed on the surface of electrode 1 becomes an electrical insulator and functions as A dielectric only when the electrode on which formed becomes anode. Therefore, electrolytic capacitors are, in principle, capacitors with polarity.
- 15. Tantalum's area most unusual process that yields a high reliable electrolytic with along life. Tantalum pentoxide powder is mixed with a manganesedioxide electrolyte and formed into a "pellet" forming the dielectric and the positive electrode plate. Graphite or silver plating forms the negative plate. This "pellet' forms a YHU
- 16. Like electrolytic capacitors, tantalumcapacitors are also polarised and. However this type of capacitor is very intolerant of being reverse biased, often exploding when placed under stress. This type of capacitor must also not be subject to high ripple currents or voltages above their working voltage. They are available in both leaded and surface mount formats. Range Offer a very high capacitance level for their volume
- 17. Silver mica capacitorsare not as widely used these days, but they still offer very high levels of stability, low loss and accuracy where space is not an issue. They are primarily used for RF applications . Range They are limited to maximum values of 1000 pF. 2.2 pF to 47nF. Uses They are primarily used for RF applications
- 18. Polyester film capacitorsare used where cost is a consideration as they do not offer a high tolerance.. Uses They are generally only available as leaded electronics components.
- 19. This typeof capacitor is a essentially a form of polyester film capacitor where the polyester films themselves are metallised. The advantage of using this process is that because their electrodes are thin, the overall capacitor can be contained within a relatively small package The metallised polyester film capacitors are generally only available as leaded electronics components.
- 20. Glass capacitors: Asthe name implies, this capacitor type uses glass as the dielectric. Although expensive, these capacitors offer very high levels or performance in terms of extremely low loss, high RF current capability, no piezo-electric noise and other features making them ideal for many performance RF applications.