Inductor

An inductor is a coil of wire which may have a core of air, iron or other ferrous materials. Its electrical property is called inductance and the unit for this is the henry, symbol H. 1 Henry is very large so mH and µH are often used, 1000µH = 1mH and 1000mH = 1H. Iron and ferrite cores increase the inductance since they can become magnetized. Inductors are mainly used in tuned circuits and to block high frequency AC signals (they are sometimes called chokes).

They pass DC easily, but block AC signals, exactly the opposite of capacitors.

Inductance is a property that is possessed by all coils of wire containing electrical current. The current creates a magnetic field, which can in turn induce current flow if the original current decreases in magnitude or stops. Essentially, an inductor is like a capacitor, only stores energy in a magnetic field instead of an electric field. This makes it very useful for power supply filters that help maintain a fairly noiseless current. A transformer is essentially two inductors, where current flow through one inductor induces current flow in the second as a result of the magnetic field.

Inductors are most often found in audio electronics, power supplies, and radio tuning circuits. An inductor can easily be made by winding insulated wire around a ferrous rod. Thin gauge wire is easiest, since it can bend into smaller loops and is cheaper than large gauge wire.

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Resistors

Resistors are components that just about every electronic device uses. A resistor is a component that resists the flow of current. They do this by either extending the length of wire that the electricity must flow through or forcing the current to pass through a poor conductor, such as carbon. The reduction in current flow can be useful in a number of ways:

It can protect components that have a specific current rating

It can change the function of the circuit

It can create a "dummy load" for a circuit in order for testing purposes

It can create by products such as heat that can be utilized for special purposes

The protection is necessary in order to prevent destruction of certain components that have a maximum current that can be passed through them. This is particularly true in components such as LEDs, which can suffer permanent damage and/or destruction if excessive current is passed through them.

The resistance can change the function of certain circuits, such as oscillators. Certain circuits use the level of current as a control for specific functions. For example, the 555 timer IC outputs pulsed electricity, the frequency of which is determined by the current level sent to one of its leads. This is very important.

The "dummy load" is useful when testing circuits in the lab since the actual load can be impractical for testing (such as a very large antenna). The resistor duplicates the resistance of the real load and makes the circuit act as though it is connected as it normally would.

Resistance creates heat losses in electrical circuits, but that is not always a bad thing. Most electrical heaters utilize this by running electricity through resistors with very low resistance, producing a lot of heat.

On a circuit diagram normally a resistor will have a letter after the value, for values less than 1,000, an ‘R’ is used. So 100 ohms will read 100R. From 1,000 ohms a ‘K’ is used and the number is divided by 1,000. So 1,000 ohms is read as 1K, 22,000 as 22K and 100,000 ohms as 100K. Lastly, from 1,000,000 ohms a ‘M’ is used and the number is divided by 1,000,000. So 1,000,000 ohms is 1M of course. Resistors are too small to have these numbers printed on them, instead they have coloured bands, which is explained further down.

Resistor values with a decimal point in circuit diagrams are expressed in 2 ways, say the circuit requires a 1.2k ohm resistor. The diagram might have it as 1.2K or it might appear as 1K2. The ‘K’ is put in place of the decimal point to prevent the value from being misread as 12K ohms. For resistors below 1k ohm an ‘R’ is used in place of the ‘K’. So 5.6 ohm resistor on the diagram would appear as 5.6R or 5R6.

The above is a picture of a 4-band 1/4w carbon film resistor. These are the most commonly used in electronic circuits due to their low cost and versatility. They come in 1/4w, 1/2w and 1w. You can tell the difference in power handling by the physical size of the package. A 1/4w resistor 7mm long by 2mm diameter, a 1/2w is about 9mm long by 3mm diameter and a 1w is 11mm long and 4mm in diameter. They usually have a tolerance of 5%.

These are 5-band metal film resistors, they have a much smaller tolerance than carbon film resistors, these have a tolerance of 1%. These are used where you need an exact value, such as a high quality audio preamplifier.
This is a ceramic wire wound resistor. They usually come with a power rating of 5w and 10w. These are used where a lot of power is going to be dissipated, such as that of a dummy load. They will be used in a high power audio amplifier.



This is wire wound nichrome wire. The purpose of nichrome wire is to produce heat and hence it’s used in electric heaters and stoves. Nichrome wire normally has a resistance of about 13.8 Ohms per metre. This coil came from a 2400w, 240v fan heater, it had 8 lengths just like the one pictured and they were used in series and parallel combinations to achieve low, medium and high power. The wire actually had a faint red glow on full power. Nichrome wire in heaters should be protected so stray hands don’t touch them, because that stray hand will get burnt.

Because carbon resistors are so small it’s impractical to print the resistance on it so instead they have 4 or 5 coloured bands. The number of bands relates to the tolerance of the resistor, the tolerance is how much variation there is likely to be. At 5% a 100 ohm resistor can be as low as 95 ohms or as high as 105 ohms. 4 bands are used when the tolerance is 5% or 10% and 5 bands are used when the tolerance is 1% or 2%. The 5th band is used to achieve more precision.


The 1st, 2nd (3rd) and multiplier bands are bunched together so you can see where to start from. This is helpful especially with 5-band resistors, which is harder to tell because the tolerance band is brown or red.

Article written by Mojo'D

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Capasitor

Capacitors are among the most commonly used components in electronics.
Their construction is fairly simple, two metal plates and a dielectric layer
separating them. Capacitors are very similar to batteries since they store
electrical charge. However, capacitors must be charged with electricity, unlike
batteries which produce their own using chemicals.

The capacitor's charge capacity depends upon the size of the metal plates.
The larger the plates, the higher the charge and vice versa. The dielectric
can be anything that disallows the plates from touching each other and discharging,
but still allows the electric force to pass through. When charged, a capacitor
gains the same voltage as the power source that was used to charge it.

The storage rating of a capacitor is based on the Farad unit. A capacitor
with a capacitance rating of one Farad is capable of storing one coulomb of
charge (6.25 x 10 ^ 18 electrons) at 1 volt. Although that many electrons
seems like a lot, it can only power an average incandescent light bulb for
about a minute.

The reason capacitors are used is often because of their quick discharge ability.
A chemical reaction in a battery takes time, while the capacitor requires
no chemical reaction to discharge electricity. This makes the capacitor a
lot faster when it comes to discharging. That is why capacitors are used in
cameras and lasers to create a bright flash, rather than batteries.

Capacitors are also used to make DC voltage constant. In power supplies, the
voltage can vary. With a capacitor included, it makes up for a lack of voltage
and absorbs the excessive voltage. This is necessary in sensitive electronic
devices that require constant voltage supplies.

Capacitors are also used to block direct current. Since a capacitor connected
in series with a power source is essentially a broken circuit, current cannot
flow, once the capacitor is charged. However, alternating current can still
flow when connected to a capacitor, since the voltage shifts and the capacitor
charges and discharges. When capacitors are connected in parallel the total
capacitance in the network is the sum of all the capacitance, Ct = C1+C2…+Cn.
For example if C1 was 10uF and C2 is 47uF the total capacitance is 57uF.

Two capacitors in parallel

When capacitors are connected in series the capacitance is
given by 1/Ct = 1/C1+1/C2…+1/Cn.

Two capacitors in series
Capacitors are usually connected in series to increase the total

voltage that can be connected between them; this is common with Tesla Coil
Circuits as finding a capacitor with the exact capacitance and voltage would
be almost impossible to find.

Special care must be taken with high voltage capacitors, such as capacitors
where mains voltages (110-120v and 220-240) or the capacitors used in microwaves
and TV sets and they can store enough charge to kill. Capacitors can store
a charge for years after the power supply has been disconnected and the terminals
should be shorted to remove the charge, some high voltage capacitors have
‘bleed resistors’ in them to drain the
charge when the power is disconnected.
The different types of capacitors are generally named by the dielectric used
in them, and have different purposes.

Aluminium electrolytic capacitors consist of one plate that is a chemical
electrolyte and a dielectric that is an oxide on one side of the other metal
plate. Aluminium electrolytic capacitors store the most charge in the smallest
space with respect to other types of capacitors due to the oxide dielectric's
amazing properties as an insulator. There are two main types of capacitor
structural designs that you will run into when working with electronics. The
two types are radial and axial. The radial design has both leads coming out
of the same side of the capacitor. The axial design has one lead coming out
of the center of each side, creating an axis.

An axial capacitor

Electrolytic capacitors are polarised, they can only be connected
one way around. The polarity is indicated on the case of the capacitor, in
most cases it will have an arrow pointing to the negative lead, but there
are capacitors with arrows pointing to the positive as well. In the picture
above the polarity arrow can be seen and is pointing to the negative terminal.
The negative lead will also be shorter than the positive lead.

A radial capacitor

These capacitors are used in power supplies to smooth the voltage
and anything that requires large energy storage, their capacity can range
from as little as 0.22uF for filtering in audio circuits and they can have
capacities beyond 10,000uF and even 100,000uF for filtering power supplies.
Its impractical to use anything beyond 10,000uF capacitors in most cases as
they are quite large and heavy. Almost all power supply circuits work satisfactorily
with 2200uF.

The 100,000uF capacitor dwarfs the 33uF capacitor

Care must be taken to ensure electrolytic capacitors are not
connected in reverse polarity, if they are the dielectric dissolves which
allows high current to pass though the electrolyte which will vaporise and
the built up pressure will be released with the capacitor bursting open with
a loud bang if the capacitor is relatively small to the sound of an explosive
detonating for large filter capacitors (3300uF or so). In some situations
where reverse polarity will occur a special Bi-Polar electrolytic capacitor
is used. They can be identified by having no polarity markings and have the
letters ‘BP’ printed on the case.

A variation on the electrolytic capacitor is the Tantalum capacitor, which
uses tantalum film instead of aluminium. Tantalums contain electrolyte in
dry form and are more resistant to reverse polarity than electrolytic but
the polarity must still be correct.

A Tantalum capacitor

Ceramic capacitors also known as disc capacitors as they look
like small discs offer small capacitances, the lowest being 1pF which is an
extremely small storage capacity. They are used in bypassing and filtering
circuits.

Polyester capacitors, also known as ‘Greencaps’
because of their appearance are the most common general purpose capacitor.
Their values range from 10nF to 0.33uF or green caps and up to 10uF for MKT
polyester capacitors.

Left: A polyester greencap capacitor; Right: Two ceramic disc capacitors

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Transformers

Transformers are devices that utilize the property of inductance to step-up or step-down voltages. Transformers, however, only work with alternating current, since inductance only occurs when a magnetic field is changing, which is not the case with direct current. However, transformer usage is not limited to voltage modification, it is also capable of matching impedances between different electrical circuits, mating balanced and unbalanced circuits, and isolating dc between circuits, while allowing ac to pass.

The basic construction of a transformer consists of two seperate coils of wire wrapped around a core of iron, air, or any ferromagnetic material. While iron and ferromagnetic cores provide much higher coupling (efficiency of induction transfer), there are significant losses through heat generation in the core. Cores can also be shaped differently, such as the rod and E-core designs. The voltage modification is caused by the difference in number of coils on each wire. The wire you have the supply voltage on is referred to as the primary winding. The wire that is receiving the modified voltage is the secondary winding. The level of modification is determined by the ratio of turns between the primary and secondary windings. Current limiting is also provided by the gauge of the wire used in the windings. A thicker gauge wire allows higher amounts of current to go through, while a smaller gauge allows less. Transformers are the primary reason that power transmission and household outlets utilize alternating current. This is because transformers allow for efficient changes in voltage that allow power to be transferred all over the world at high voltages and low costs.

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Optoisolators

Optoisolators are circuits designed to isolate one circuit from another using light. Why would you use light instead of implementing some diodes or voltage regulators? Because light is essentially a guaranteed protection. If an overvoltage or overcurrent is applied to the optoisolator, the optoisolator circuit is destroyed and the circuit(s) it was protecting will not be affected.

The most common optoisolators are placed in an integrated circuit for convenience and efficiency. The most popular model is the 4N33, which is housed in an 8-pin DIP package. The 4N33 internally is basically an LED next to a phototransistor. This could be called an optical modem, since it modulates the electric signal into light waves, which are demodulated by the phototransistor as it converts the light into electricity again.

To design a circuit using an optoisolator, you cannot ignore the components inside of it. On the input circuit, you must take the forward voltage of the LED into account, which can be approximated to .7 volts. On the output side, you should take the phototransistor's forward voltage into account and it can be approximated to .2 volts. If you are working with relatively high voltages, you will need a resistor on the input to protect the LED.

Optoisolators are commonly used to protect expensive circuits from voltage and current surges. One example application would be on the output of a microprocessor. Most microprocessors can't output a very high current, but you might want to be able to power a motor with an output pin. To work around this problem, you could connect the output pin to the optoisolator's input and then connect the motor in series with the output and a voltage supply that is high enough to power the motor. This way, the majority of the current is coming from the independent power supply rather than the microprocessor.

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