Capacitors are basically
two parallel metal
plates separated by an
insulator.
This insulator is called
the dielectric.
Capacitor types are
named after the
dielectric. Thus we have
ceramic, mica,
polyester, paper air
capacitors etc.
Capacitors can be charged up and store electricity, similar to a car battery. This can be a hazard if they are charged up to high voltages. If it is necessary, capacitors with large charges should be discharged via a resistor to limit the discharge current. DC current cannot flow through a capacitor since the dielectric forms an open circuit.
Capacitors come in all shapes and sizes and are usually marked with their value. Values are measure in Farads. Values in Farads are unusual. Most capacitor values are measured in microfarads, nanofarads or picofarads. See the page on Value multipliers to find out more about this.
They are often marked
with their maximum
working voltage. The
voltage across the
terminals must not
exceed this value. It is
OK to use a voltage
below the maximum value.Some capacitors such as
electrolytic and
tantalums are polarised.
This means that they
must be fitted the
correct way round. They
are marked to indicate
polarity.
Some values are indicated with a colour code similar to resistors. There can be some confusion.
A 2200pf capacitor would have three red bands. These merge into one wide red band.
Some values are marked
in picofarads using
three digit numbers. The
first two digits are the
base number and the
third digit is a
multiplier.For example, 102 is 1000
pF and 104 is 100,000 pF
= 100 nF = 0.1 uF.
To find the total value of capacitors in parallel (that is connected across each other) their values are added. To find the total value if they are in series (that is in line with each other) then the following formula is used.
1/C total =1/C1 + 1/C2 + 1/C3 etc
Variable capacitors are available in which the value can be adjusted by controlling the amount of overlap of the plates or the distance between them.
There is a type of diode
called the Varicap diode
with similar
characteristics.
Capacitors can be charged up and store electricity, similar to a car battery. This can be a hazard if they are charged up to high voltages. If it is necessary, capacitors with large charges should be discharged via a resistor to limit the discharge current. DC current cannot flow through a capacitor since the dielectric forms an open circuit.
Capacitors come in all shapes and sizes and are usually marked with their value. Values are measure in Farads. Values in Farads are unusual. Most capacitor values are measured in microfarads, nanofarads or picofarads. See the page on Value multipliers to find out more about this.
Some values are indicated with a colour code similar to resistors. There can be some confusion.
A 2200pf capacitor would have three red bands. These merge into one wide red band.
To find the total value of capacitors in parallel (that is connected across each other) their values are added. To find the total value if they are in series (that is in line with each other) then the following formula is used.
1/C total =1/C1 + 1/C2 + 1/C3 etc
Variable capacitors are available in which the value can be adjusted by controlling the amount of overlap of the plates or the distance between them.
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