10 capacitors
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Transcript of 10 capacitors
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Capacitance/Capacitors
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Capacitance
• Capacitance is the ability of a dielectric (insulator) to store an electrical charge
• Charge = Coulomb = Q = 6.25 X 1018 electrons
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Capacitors• A capacitor is a component that stores electrical
charge• Schematic
• Make up of a capacitor
• The unit of measurement for capacitance is the Farad
Note to teacher: charge up a 470 µF cap to 30v and then discharge
Dielectric (Insulator) 2 Conducting Plates
Non-Polarity Sensitive Polarity Sensitive+
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Farad• 1 Farad: when 1 coulomb is stored in a dielectric
with a potential of 1 volt
• 1 Farad is a very large value• Typical values of capacitance are in:
– microfarads (μF) (10-6) – picofarads (pF) (10-12)
• Higher farad value = more stored charge– Note: Charge up 470 μF and 1000 μF to show difference
1 coulomb 1 VoltFarad=
CoulombVolt
C=QV
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How Capacitors Work
• http://micro.magnet.fsu.edu/electromag/java/capacitor/index.html
Charging Storing a charge
Discharge
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Factors affecting Capacitance: The ability of a capacitor to store electrical charge (capacitance size) depends upon
1. Size (surface area) of the plates– Larger plate area = more capacitance
2. Distance between the plates– Capacitance increases as the width decreases
3. Dielectric MaterialAir = 1Paper = 2-6Ceramics = 80 – 1200Mica = 3-8Mylar = 2-3Electrolytic = 7
• http://micro.magnet.fsu.edu/electromag/java/capacitance/index.html
100 μF 200 μF
200 μF100 μF
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Three Important Facts When Choosing a Capacitor
1. Capacitance Value2. Voltage Rating3. Polarity
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Capacitance ValueRules of thumb (as in 99% of the time)1. MF or mF on an old capacitor = µF .2. If a capacitor has a value of 1 µF or more it is usually an
electrolytic (canister) capacitor. Conversely, if the capacitance value is less than 1 µF it is usually a disc or chicklet variety.
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Capacitance Values of Disc CapacitorsThe value of the disc capacitors is usually given in one
of two methods. 1. The capacitance value is sometimes printed on the
face of the disc capacitor like the following. If this is done then the value of the capacitance is given in micro farads (µF).
.1 Z .047 k
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Capacitance Values of Disc Capacitors2. The capacitance value is sometimes printed in
code on the face of the disc as shown below. If this is the case then the capacitance value is given in picofarads (pF). The code given is the same as the code used to determine resistor values. For example: 102 would represent1= 1st digit of value, 0 = 2nd digit of value, 2= multiplier (how many zeros)
Therefore 102 = 1000 picofarads (pF) or .001 micro farads (µF)
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Capacitors in Series and Parallel• Capacitors in Series
• Capacitors in Parallel
10 μF 10 μF
CT = 5 μF
10 μF 10 μF
CT = 20 μF
Notice that they are exactly opposite of resistors!!!!!!!!
In series the width of the dielectric is additive
In parallel the plate surface area is additive
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Resistor/Capacitor Time Constants