Electronic Components

Passive Components

Passive components are electronic components that do not require any form of electrical power to operate. As these devices are passive, they do not provide gain, amplification, or directionality to a circuit, instead of that they result in attenuation (in this case, the reduction of an electric current also used to refer to the reduction in the magnitude of a radio signal or any other oscillation). Passive components do not generate energy but can store it or dissipate it.

Passive devices can be used individually or connected together within a circuit, either in a series or in a parallel combination to control complex circuits or signals, produce a phase shift to the signal, or to provide some form of feedback, but they can not multiply a signal by more than one as they have no power gain. Passive devices are bi-directional components, which is why they can be connected either way around within a circuit unless they have a specific polarity marking, such as electrolytic capacitors. The polarity of the voltage across them is determined by conventional current flow from the positive to the negative terminal. Examples of passive components include resistors, capacitors, diodes, inductors, and transformers.

Resistors

A resistor is an electronic component that resists the flow of electrical current. It is a passive device used to control, or impede the flow of electric current in an electric circuit by providing resistance, thereby creating a drop in voltage across the component. The resistor is the most widely used component in electronic circuits.

While the appliances and devices connected in a circuit also offer resistance to the flow of current; however, sometimes their resistance is not enough to reduce the current flow sufficiently for the voltage applied to the circuit. For example, if a light bulb does not offer sufficient resistance, more current than is necessary will flow through the bulb, causing it to burn brighter and reducing its lifespan as it will burn out faster than it should. In addition to a measured resistance to the circuit in the form of a resistor, the component will reduce the current flow to an optimal value. Components known as variable resistors can also be used to allow the resistance to be increased or decreased by external control, causing the light bulb to burn brighter or dimmer, as required.

The value of a resistor is measured in ohms and represented by the Greek letter capital omega (Ω). Resistors usually have a brown cylindrical body with a wire lead on each end and colored bands that indicate the value of the resistor. Resistor values range from as low as 1 ohm to 9 megaohms.

Capacitors

Capacitors are components that store small amounts of electrical energy when a current is passed through it. Capacitors contain two electrical conductors, often in the form of metallic plates separated by a dielectric medium. A dielectric medium is very similar to an insulator, in which it does not allow current to pass through, but there is one difference. In dielectric materials, electric polarization occurs when a voltage is applied across it, and a current flows through it. Polarization occurs when positive charges are pulled to one side and negative ones to the other side. This separation of charges results in a build-up of energy in the capacitor.

The separation is maintained while the current is flowing. The current may stop the charges from moving towards each other due to the force of attraction, and the energy will be released in the form of a current.

Materials commonly used as dielectrics include glass, ceramic, plastic film, paper, and mica. The effect of a capacitor is known as capacitance. The unit of measurement for capacitance is Farad, but this unit is much too large for practical work. It is usually measured in microfarads (μF) or picofarads (pF). The ability of capacitors to store energy is useful in electronic devices in many ways. One of the main uses of a capacitor is to ensure a steady DC voltage is applied across a circuit or a component. These are referred to as decoupling capacitors and act as a very small and local power supply for components. If the power supply drops very temporarily, its voltage a decoupling capacitor can briefly supply power at the correct voltage. The circuit or the component is then shielded from these voltage fluctuations, thus allowing the circuit to function with interruption and protecting its components.

Capacitors are connected between the power supply and ground, in parallel with the component. While this appears as a short circuit connection between power and ground, capacitors only allow high-frequency signals to pass through the DC signal will go to the component as required. They also serve to clean the supply of unwanted noise.

In some applications, like the flash of a camera, you need a sudden release of energy to power the flashbulb. It is precisely what a capacitor does. The capacitor is charged by the power supplied from the batteries, in the camera, and it holds its charge. When you press the button on the camera to take a picture, the circuit between the capacitor and a flashbulb is closed, which causes the energy from the capacitor to be released in a burst and that lights up the flashbulb for the brief time required or a flash.

Active Components

An active component can amplify a signal or produce a power gain. All active components require a source of energy, which generally comes from a DC circuit. An active component works as an alternating-current circuit in a device, which works to increase the active power, voltage, or current. An active component can do this because it is powered by a source of electricity, which is separated from the electrical signal. An active device can control electron flow and either allows voltage to control the current or allows another current to take control.

Transistors

A transistor is a semiconductor component used to amplify or switch electrical current. It is composed of semiconductor materials and usually has at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals controls the current through another pair of terminals. As the output power can be higher than an input power, a transistor acts as a signal amplifier. Alternatively, the transistor can be used to turn current on or off in a circuit as an electrically controlled switch, where the amount of current is determined by other circuit elements.

There are two types of transistors, which have slight differences in how they are used in a circuit. A bipolar transistor has terminals labeled base, collector, and emitter. A small current at the base terminal (that is, flowing between the base and the emitter) can control or switch a larger current between the collector and emitter terminals. For a field-effect transistor, the terminals are labeled gate, source, and drain, and a voltage at the gate and drain can control a current between source and drain. Transistors make excellent electronic switches as they can turn currents on and off billions of times per second. Transistors are the key active components in practically all modern electronics. Combinations of transistors with other electronic components form circuits usually function from something as simple as a timer to something as complex as a computer processor. Computer processors use transistors as a basic mechanism for processing, storing, and moving data.

Transistors are interconnected to create what are known as logic gates that allow Boolean logic functions to be performed by electronic devices (AND, OR, NOT, and so on with digital values to provide processing logic on data).

Transistors are generally packaged into what is known as integrated circuits. An integrated circuit (also referred to as an IC or a chip) is a complex electronic circuit assembled on a small flat piece (or chip) of semiconductor material, such as silicon. It is orders of magnitude smaller, faster, and less expensive than a similar circuit constructed of discrete electronic components. ICs are now used in virtually all electronic equipment and have revolutionized the world of electronics. The affordable, compact, and high-performance computers, mobile phones, and other digital home appliances we use today have been made possible by integrated circuits.

Diodes

A diode is defined as a two-terminal electronic component that only conducts current in one direction. A diode has very low resistance in the one direction and very high resistance in the reverse direction. A diode is effectively like a valve for an electrical circuit.

Semiconductor diodes are the most common type of diode. These diodes begin conducting electricity only if a certain threshold voltage is present in the forward direction (the low resistance direction). The diode is said to be forward-biased when conducting current in this direction. When connected within a circuit in the reverse direction (the high resistance direction), the diode is said to be reverse-biased.

A diode’s working principle depends on the interaction of p-type and n-type semiconductors. A p-type semiconductor has an excess of holes, while an n-type semiconductor has an excess of electrons. The terminal connected to the p-type material is called the anode, and the terminal connected to the n-type material is called the cathode.

An ion is an atom or molecule that has a net electrical charge. Since the negative charge of an electron is equal to the positive charge of a proton. The net charge of an ion will either be negative or positive, depending on whether the number of electrons is greater or less than the number of protons.

When a p-type and an n-type semiconductor are connected, it forms a P-N junction. Without any external voltage applied, the excess holes in the p-type area and the excess electrons in the n-type area will get attracted to each other and recombined into immobile ions creating a space between the p-type and n-type areas known as the depletion region. These immobile ions resist the flow of electrons or holes through them, which now acts as a barrier between the two materials. The width of the depletion region depends upon the doping concentration in the materials.

When a voltage source is applied to the diode with the positive terminal connected to the anode (or p-type area) and the negative terminal to the cathode (or n-type area), the diode is said to be forward-biased. In such a circuit, the holes and electrons in both regions get repelled since a voltage of the same charge has been applied. The holes and electrons get pushed into the depletion region and change the neutrality of the immobile ions, which move back into either the p-type or n-type areas, gradually decreasing the width of the barrier. When the applied voltage is greater than or equal to what is known as the cut-in voltage, an entire barrier is removed, and the electrons and holes are now free to cross the junction, which enables the flow of current.

If the power supply connections are reversed so that the negative terminal of a voltage source is applied to the anode and the positive terminal to the cathode, it is said to be reverse-biased.

Now, the holes and electrons both get attracted to their own side, allowing the holes and electrons around the depletion layer to continue combining into immobile icons. The width of the depletion region now gradually increases, preventing electrons and holes from crossing the junction, which stops the flow of current. There are several applications of a diode, including amplification, switching, conversion of electrical energy into light energy, and light energy into electrical energy. Diodes are considered passive or active components depending on their function.

Some of the more common diodes are:

• Light Emitting Diode (LED): An LED works as a simple diode, but various combinations of semiconductors are used to generate different colors. In the forward-biased mode, when the electron and hole recombination takes place, a resultant photon gets released that emits light. Different semiconductor and doping material combinations emit different colors.

• Photodiode: These types of diodes convert light into an electrical current. A photodiode is designed to operate in reverse bias. When photons (particles of light energy) enters the depletion region of the diode, they hit the ions with high energy-releasing some electrons and creating holes. The electrons and holes get attracted to the cathode and anode respectively (since the diode is reverse-biased), causing the flow of current.

Photodiodes are similar to regular semiconductor diodes except that they expose an area to allow light to reach the sensitive part of the device. Smaller and simpler photodiodes are used to detect light, while large and complex photodiodes are used as solar cells to generate electricity from sunlight.