The RJ Journal - Electronics

We shall not go too deep into the details about the physics behind electricity but some basic things must be understood before we can go on to learn about the electronic components.

Electric voltage is the power that drives the free electrons in an electric conductor and thereby creates a current. Voltage is the difference in electric potential between two points in an electric circuit. When these two points are connected, the current flows from the most positive point to the most negative point, trying to neutralize the potential difference. In analogy with the closed water pipe system, the voltage in an electric circuit is like water pressure in the pipe system.

The difference in electric potential, the electric voltage, is written with the letter U and is measured in volts (V) and it is always measured between two points - a reference point (ground or 0V, for instance) and the point where the voltage is to be known. The voltage in that point is then said to be so and so many volts with respect to the reference point. The voltage for a certain point in a schematic diagram can then be written as U2=50V.

There are two kinds of voltages - DC and AC. DC stands for Direct Current and AC for Alternating Current. DC means that the voltage is at a steady level and the current is only flowing in one direction. AC means that the voltage is constantly changing between positive and negative with respect to the reference point. The change is cyclic and the magnitude and direction usually follows the shape of a sinus wave.

Two symbols that can be used to show a DC and an AC voltage source in a schematic diagram. The DC voltage symbol is also the symbol for a battery.
Electronic circuits are mostly powered with a DC voltage in the range of 3 to 30V (and even lower for high frequency digital IC's such as CPU's). Digital logic circuits has usually been powered with 5V but nowadays it is also common to have 3.3V circuits. The electric system in a car operates at 12V and 24V is a common voltage for industrial systems.

AC voltage is mostly used to distribute power to businesses and residences. All electrical wall outlets in an ordinary house has AC voltage. This voltage is also much higher than electronic circuits can use directly, mostly 115VAC or 230VAC with a cyclic rate of 60Hz or 50Hz (cycles per second). When the value for an AC voltage is given, it is mostly given as the RMS value. The RMS value is the equivalent value for a DC voltage which would give the same power as the AC voltage in the same resistive load. The peak voltage (positive and negative) is roughly 1.41 times the RMS voltage for a sinusoidal AC voltage.

The human body is sensitive to voltage and current and a high enough voltage can cause serious injury and even death. Because of this there are strict regulations for voltages that can be dangerous. One of the European normative standard for electrical safety, EN-61010, states that a voltage has to be less than 33V RMS or 46.7V peak for AC and less than 70V for DC in order to be safely touchable.

The voltage is not only used to power electronic circuits, it is also used to represent real world quantities which are transformed to voltage levels by different kind of sensors and transducers. Examples of such sensors are microphone, pressure sensor, light sensor, temperature sensor, mechanical position sensor, magnetic sensor and so on. Even an electric switch on an instrument panel can be said to convert the mechanical position to one of two voltages which in turn can make an electronic circuit work in one of two ways. In digital circuits, a voltage above a certain threshold level is used to represent a "1" and a voltage below a certain, lower, threshold level is representing a "0".

The breakdown voltage of an insulator is the voltage level, where the insulator breaks down and lets current pass through it. The thicker the insulator is, the higher it's breakdown voltage is. Air is also an insulator and it too has a breakdown voltage. It's thickness is the distance between the two conductors of different potential. When the potential difference, the voltage, becomes higher than the breakdown voltage, a spark between the two conductors is formed and the current can flow between the two conductors. The breakdown voltage for air is about 1000V per mm and is depending on air pressure and humidity. The breakdown voltage also gets lower if the conductors has sharp edges.

Electronic circuits and components has a maximum operating voltage. If this voltage is exceeded, the component will break. Therefore it is important to know this limit and make sure that the component will not be subjected to higher voltages in the circuit.

Where does voltage, or electricity, come from then? Electricity can either be created chemically or mechanically. A battery is a chemical voltage source which could either be rechargeable or non-rechargeable. The voltage potential in a battery is created as a result of a chemical reaction inside the battery. This chemical reaction can be reversed in a rechargeable battery by applying a reversed electrical current through the battery. Mechanically created voltage, or electricity, is created in electrical generators. By moving a conductive wire through a magnetic field, a potential voltage difference is generated in the wire and this voltage can in turn create an electric current. The opposite is also true, an electric current that is flowing is also generating a magnetic field. This magnetism is used to drive electric motors. Electric generators are mostly driven by turbines which gets their movement from pressurized steam created from heat in a power plant or directly from flowing water in a hydroelectric power station. These generators supply the power grid throughout the country with electricity and that electricity finally ends up in a power outlet in your home.

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