Last article we introduced Capacitor's definition and classify.
Now we introduce the function fo capacitor.
the DC circuit, the capacitor is equivalent to the disconnection. A
capacitor is a device capable of storing electric charge, is one of the
most commonly used electronic components.
It must start with the
structure of the capacitor. The simplest is by the capacitor plates and
the intermediate ends of the insulating dielectric (including air)
configuration. After energization, the charged plate, forming a voltage
(potential difference), but since the intermediate insulating material,
so the entire capacitor is not electrically conductive. However, this
situation is not exceeded in the threshold voltage of the capacitor
(breakdown voltage) of preconditions. We know that any substances are
relatively insulated, to increase when the voltage across the substance
to a certain extent, the material can be electrically conductive, we
call this voltage is called the breakdown voltage. Capacitance is no
exception, after the capacitor is the breakdown, it is not an insulator
of. However, at the secondary level, this voltage is not seen in the
circuit, so are operating below the breakdown voltage, can be used as an
insulator to see.
However, in AC circuits, because the direction
of the current over time as a function of certain changes. The process
of charging and discharging the capacitor is a time, and this time, the
changing electric field between the plates is formed, and this is also a
time-varying electric field is a function. In fact, the current is in
the form of an electric field between the capacitor through.
At the secondary level, there is a saying, called through exchanges, DC blocking, that is the capacitance of this nature.
capacitors provide energy storage devices for local devices, which
enables the regulator output uniformity, reduce the load demand. Like
small rechargeable batteries, bypass capacitors can be charged to the
discharge device. To minimize impedance bypass capacitors as close as
possible load device power supply pins and ground pins. This can well be
prevented ground elevation and excessive noise input values caused.
Ground is connected to the voltage drop at the time by the large current
Decoupling, also known as
decoupling. From the circuit, it can always be divided into the driving
source and the driven load. If the load capacitance is large, the
driving circuit charging the capacitor should discharge to complete the
transition signal, the rising edge relatively steep when the current is
relatively large, so that the drive current will absorb a large supply
current in the circuit inductance, resistance (especially on the pin
inductance chip) will have to rebound, this current is relative to the
normal situation, it is actually a noise, it will affect the normal
operation of the preceding stage, which is called "coupling."
capacitors is to play a "battery" role, to meet the current drive
circuit changes, to avoid mutual interference coupling in the circuit to
further reduce the impedance of the power frequency interference
between the reference ground.
The bypass capacitors and
decoupling capacitors combine more readily understood. The actual bypass
capacitor is decoupled, but generally refers to bypass high frequency
bypass capacitor, which is provided to the high frequency switching
noise in a low impedance discharge pathway. High frequency bypass
capacitors are generally relatively small, according to the resonant
frequency is generally taken 0.1μF, 0.01μF etc; away coupling
capacitance for generally higher, may be 10μF or greater, based on
distributed parameter circuit, as well as changes in the size of the
drive current determined. Bypass is the input signal as filtered
interference objects, the decoupling is to filter out the interference
of the output signal as an object, to prevent the interference signal
power return. This should be the essential difference between them.
theory (which assumes a pure capacitance capacitors) that the larger
capacitance, impedance is smaller, the higher frequency through. But in
fact more than 1μF capacitor mostly electrolytic capacitors, inductors
have great ingredients, so instead of the high frequency impedance will
increase after. Sometimes see a larger capacitance electrolytic
capacitor in parallel with a small capacitor, then a large capacitor
filter low frequency, high frequency small capacitor filter. Capacitance
effect is through the exchange of DC blocking, pass the high-frequency
low-resistance. More easily by the high-frequency capacitance increases.
Specifically for use in filtering, large capacitor (1000μF) filter
low-frequency, low capacitance (20pF) filter frequencies. Users had the
image of the filter capacitor as a "pond." Because the voltage across
the capacitor is not mutated, can be seen, the higher the frequency the
greater the attenuation can be the very image of said capacitor like a
pond, not by the addition of a few drops of water or evaporation of
water caused by the change. It is converted to variable voltage change
in the current, the higher the frequency, the greater the peak current,
thereby buffering the voltage. Filtering is charging and discharging
Energy storage capacitor through a
rectifier charges collected, stored and transmitted by the transducer
leads to the power supply output. Voltage rating of 40 ~ 450VDC,
capacitance values between 220 ~ 150 000μF electrolytic capacitors is
more commonly used. Depending on the power requirements of the device
sometimes used in series, parallel or a combination thereof, for the
power level than 10KW power, usually a larger volume of the tank-shaped
screw terminal capacitors.
Please wait Capacitor 3. ^_^