6 Electronics

Electronics is the branch of science and technology which makes use of the controlled motion of electrons through different media and vacuum. The ability to control electron flow is usually applied to information handling or device control. Electronics is distinct from electrical science and technology, which deals with the generation, distribution, control and application of electrical power. This distinction started around 1906 with the invention by Lee De Forest of the triode, which made electrical amplification possible with a non-mechanical device. Until 1950 this field was called "radio technology" because its principal application was the design and theory of radio transmitters, receivers and vacuum tubes.

Types of Power Supply

There are many types of power supply. Most are designed to convert high voltage AC mains electricity to a suitable low voltage supply for electronics circuits and other devices. A power supply can by broken down into a series of blocks, each of which performs a particular function.

For example a 5V regulated supply:

Each of the blocks is described in more detail below:

• Transformer - steps down high voltage AC mains to low voltage AC.
• Rectifier - converts AC to DC, but the DC output is varying.
• Smoothing - smooths the DC from varying greatly to a small ripple.
• Regulator - eliminates ripple by setting DC output to a fixed voltage.

Transformer only

Transformer + Rectifier

Transformer

• Step-up transformers increase voltage, step-down transformers reduce voltage. Most power supplies use a step-down transformer to reduce the dangerously high mains voltage (230V in UK) to a safer low voltage.

• The input coil is called the primary and the output coil is called the secondary. There is no electrical connection between the two coils, instead they are linked by an alternating magnetic field created in the soft-iron core of the transformer. The two lines in the middle of the circuit symbol represent the core.

Single diode rectifier

A single diode can be used as a rectifier but this produces half-wave varying DC which has gaps when the AC is negative. It is hard to smooth this sufficiently well to supply electronic circuits unless they require a very small current so the smoothing capacitor does not significantly discharge during the gaps. Please see the Diodes page for some examples of rectifier diodes.

Single diode rectifier	Output: half-wave varying DC (using only half the AC wave)

KINDS OF CIRCUIT
Two kinds of common circuits are: The series circuit and the parallel circuit. In series circuit, the current passes through every resistance; like for instance: 3 bulbs are put in series, if any one of them fails to let current pass through it, the remaining bulbs will also not work. Where as, in parallel circuit every resistance is connected independently. Therefore, if any of the bulbs in parallel fails to let current pass through it, the other two bulbs will continue to work.

AM RADIO KIT
This is a complete AM radio kit for the standard broadcast band, most of which is on a single IC. Other components, such as coils and variable capacitor to make a finished radio are included. The IC is the RF Amp, detector and AGC circuitry. The IC's output drives a two stage, transistor audio amplifier and 3" speaker - DIY Kit 63.

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