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# 10 capacitors

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### Transcript

• 1. Capacitance/Capacitors
• 2. Capacitance
Capacitance is the ability of a dielectric (insulator) to store an electrical charge
Charge = Coulomb = Q = 6.25 X 1018 electrons
• 3. 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
+
-
Non-Polarity Sensitive
Polarity Sensitive
2 Conducting
Plates
Dielectric (Insulator)
Note to teacher: charge up a 470 µF cap to 30v and then discharge
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:
Higher farad value = more stored charge
Note: Charge up 470 μF and 1000 μF to show difference
Q
C=
V
Coulomb
Volt
1 Volt
1 coulomb
• 5. How Capacitors Work
Charging
Storing a charge
Discharge
http://micro.magnet.fsu.edu/electromag/java/capacitor/index.html
• 6. Factors affecting Capacitance: The ability of a capacitor to store electrical charge (capacitance size) depends upon
Size (surface area) of the plates
Larger plate area = more capacitance
Distance between the plates
Capacitance increases as the width decreases
Dielectric Material
Air = 1
Paper = 2-6
Ceramics = 80 – 1200
Mica = 3-8
Mylar = 2-3
Electrolytic = 7
http://micro.magnet.fsu.edu/electromag/java/capacitance/index.html
200 μF
100 μF
200 μF
100 μF
• 7. Three Important Facts When Choosing a Capacitor
Capacitance Value
Voltage Rating
Polarity
• 8. Capacitance Value
Rules of thumb (as in 99% of the time)
MF or mF on an old capacitor = µF .
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.
• 9. .047 k
.1 Z
Capacitance Values of Disc Capacitors
The value of the disc capacitors is usually given in one of two methods.
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).
• 10. Capacitance Values of Disc Capacitors
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 represent
1= 1st digit of value,
0 = 2nd digit of value,
2= multiplier (how many zeros)