Chapter 1, The Basics
Electronics use electric power.
- A battery is a source of electric power.
- A wall socket is a source of a different kind of electric power.
- Lightning is also a (very dangerous) source of electric power.
- Sparks while combing some people's hair is called "Static electricity". Also some rugs can cause static electricity.
Voltage and Current
Electronic equipment operates by controlling the flow of electrons. Electrons are part of the atom. The atom also contains neutrons and protons. The number of protons and electrons in an atom are usually equal, but if it is not the atom is called an ion.
Electric current is the flow of charge from one place to another, reminiscent of the way ocean current is the flow of water from one place to another. Charge is like a tiny indivisible packet of electricity, and is carried by electrons. The charge on each electron is fixed, but if more electrons flow in a given time, then more charge is said to be flowing. An electron is a type of charge carrier - it carries charge, but it is not the only type. Later we will introduce another kind of charge carrier used in all electronics, so while we talk about electrons as the entity that carries charge, keep in mind that the term "charge carrier" is sometimes more appropriate.
Charge is important when we examine semiconductors, which is what real electronics is all about. Charges of the same sign (- and -, or + and +) repel each other, just as like poles of a magnet do. Conversely, unlike charges (+ and -) attract each other. This fact is very important. It is this attraction and repulsion of charge that causes charge to move in a conductor, thus creating a current.
Charge flows when there is a difference of potential between two points in the circuit. Potential difference is measured in volts and is sometimes called voltage. The larger the potential difference, the larger the flow of charge, all else being equal. A typical ordinary battery creates a potential difference of about 1.5 volts between its terminals. If the battery is not connected to anything, the potential difference is still there, and can be measured with a voltmeter. Only when a circuit is formed between the terminals of the battery will a path exist for electrons to flow, and electrons will be caused to flow. Current and voltage are linked by Ohm's Law, which is a very simple linear relationship.
Once it was believed that electrons traveled from the positive side of a battery to the negative side. However, when the technology was there to test this it was proven that electrons actually traveled from the negative terminal of the battery to the positive terminal. When talking about circuits and designing them, we use conventional current, which we measure as if charge flows from positive to negative - for practical purposes, the fact that the electrons really go the other way does not make any difference. The rest of this book follows standard practise and always assumes conventional current.
Current is measured in amperes or amps for short, though 1 amp is quite a large current so usually milliamps (1 thousandth of an amp) or microamps (1 millionth of an amp) are often used, especially in electronics.
To summarise: Current is the flow of charge. That charge can be thought of as flowing along the conductor. Voltage or potential difference is the force that gives rise to the current, and appears across a pair of points in a circuit, such as the terminals of a battery.
Conductors: Conductors are materials that are packed full of easily-movable electrons. All metals are conductors. All materials offer some resistance but that shouldn't matter for now as long as you're not using any extremely long lengths of wire.
Open/Closed/Short Circuit: An open circuit is one where there is a physical gap in the wire which does not allow charge to pass. A closed circuit is the path charge travels from one terminal of the battery to the other. A short circuit is where something like a piece of metal would fall onto two or more pieces of metal attached to the circuit and change the flow of electricity, resulting in undesired operation of the electronic device.
Circuit Diagrams: It would be nearly impossible to take a picture of a complicated electronic circuit and expect people to build the same one. To solve this problem, circuit diagrams are used. In circuit diagrams wires are represented by lines. When lines cross over each other they may be connected depending on how the diagram is drawn.
I'll try to make this book use the second example but remember to pay attention to circuit diagrams for things like that.
Electric power, energy, temperature, heat sinks, thermal resistance, and thermal capacitance
Light bulbs, for example, are rated at 25 Watt (W), 60 W, 100 W, etc. That is the Power they use if and whenever they are switched on, never mind the length of time they are on.
A 100 W light bulb that is switched on uses Energy at the rate of 100 Watthours(Wh) per hour (Wh/h), 100 Wh if one hour, 200 Wh if 2 hours, etc. One Kilowatthour(kWh) is 1000 Wh. Light from lightbulbs is only one of several forms of energy. Another form is heat. Heat is related to temperature.
There is a close relationship between energy and temperature. Electronic devices, such as diodes or transistors, have a "rating" of a number of Watts (W) at a given device temperature that must not be exceeded to prevent damage. For example in data sheets for transistors often there is a graph showing the collector current versus the collector-emitter voltage for different base currents. Always add, if it isn't there already, the power curve. For example, if a power transistor is rated at 50 W, then one point of this curve would be 10 Volt (V) x 5 Amperes (A), another 5V x 10 A, etc. If the outside temperature is higher, or there isn't a free flow of cooling air, then the power rating will be lower - this is called "derating". Often electronic equipment includes an internal fan to keep the temperature down to below rated limits under all reasonable operating conditions.
w:Heat sinks are very important; they are used to reduce the temperature of the electronic device. This is done by mounting the device on a heat sink, usually via a heat-conducting chemical paste, and, if necessary, insulating heat-conducting washers, permitting as much heat as possible to be conducted from the device to the heat sink. The heat sink, which has a comparatively large surface area in touch with not only the device, but also with cooling air, then transfers its heat to that air, thus keeping the device's temperature lower than it would be without the heat sink, and also permitting therefore a larger power rating, and a larger current rating, without causing any damage to the device.
Just as electrical resistance (in DC circuits) is voltage divided by current (Volts per Ampere), similarly "thermal resistance" is defined as degrees Celsius difference per Watt. Also "thermal capacitance" is defined as Wattseconds per degree Celsius.
- More about power
- Power in circuits
- Calculating power
- Units and their SI system
- Energy in general
- Energy meters
- Energy and electricity. Why the fuss?
- Heat Transfer and wikipedia: heat sinks , wikipedia: thermal resistance and thermal capacitance
- About temperature and units of temperature
Basic light bulb circuit: You will need a battery, low power light bulb with socket, and some wire.
Understanding the Parts
Battery: Batteries use internal stored chemical energy to push electrons from one end to the other. The battery will run out eventually when it uses up all its internal stored energy.
Light Bulb: (I plan on using an LED for the light as it does not need a socket and works with a breadboard) (what's a breadboard?) A breadboard is a plastic board with lots of holes, which electronic components pins are pushed into. The holes are electrically connected in lines. (e.g. all the vertical lines are connected together). (Practical Electronics/Breadboard)
Wires simply provide a pathway for electric current to travel
Now it's time to start building this circuit.
Connect one terminal of the battery to one terminal of the light bulb socket, and the other terminal of the battery to the other terminal of the light bulb socket. That's your first circuit.
- If the atom is missing electrons it is said to be positive (cation); if it has extra electrons it is said to be negative (anion).