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Power Stations House Generators. Alternating Current & Voltage. AC Power (Wikipedia).
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AC Power (Wikipedia) • In a three-phase system, three circuit conductors carry three alternating currents (60 Hz) which reach their instantaneous peak values at one third of a cycle from each other. This makes it possible to produce a rotating magnetic field in an electric motor. • Three-phase systems have a neutral wire. A neutral wire allows the three-phase system to use a higher voltage while still supporting lower-voltage single-phase loads. • Most household loads are single-phase.
Electrical Lab Safety • Electricity can kill you, especially alternating current! • Current can pass from your hand through your feet to ground, or through your heart to your other hand. • Capacitors can hold kilovolts of charge for years. • Static electricity, generated by your feet on a carpet, can produce kilovolts that can fry solid state electronics. • Wear shoes on a dry floor, use one hand.
Batteries • An electric battery is a device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy. • Each cell contains a positive terminal, or cathode, and a negative terminal, or anode. • Electrolytes allow ions to move between the electrodes and terminals, which allows current to flow out of the battery to perform work (wiki). • Batteries convert chemical energy directly to electrical energy.
How Batteries Work • Each cell consists of two half-cells connected in series by a conductive electrolyte containing anions and cations. • One half-cell includes electrolyte and the negative electrode, the electrode to which anions (negatively charged ions) migrate; the other half-cell includes electrolyte and the positive electrode electrode to which cations (positively charged ions) migrate. • Redox reactions power the battery. • Cations are reduced (electrons are added) at the cathode during charging, while anions are oxidized (electrons are removed) at the anode during discharge. • The electrodes do not touch each other, but are electrically connected by the electrolyte. (wiki)
Battery Types: Primary • Primary batteries, or primary cells, can produce current immediately on assembly. • Disposable primary cells cannot be reliably recharged, since the chemical reactions are not easily reversible and active materials may not return to their original forms. • In general, these have higher energy densities than rechargeable batteries. • Common types of disposable batteries include zinc–carbon batteries and alkaline batteries. (wiki)
Battery Types: Secondary • Secondary batteries, also known as secondary cells, or rechargeable batteries, must be charged before first use; they are usually assembled with active materials in the discharged state. Rechargeable batteries are (re)charged by applying electric current, which reverses the chemical reactions that occur during discharge/use. Devices to supply the appropriate current are called chargers. • The oldest form of rechargeable battery is the lead–acid battery: the modern car battery can deliver a peak current of 450 amperes. • Mobile phones and laptop computers use (in order of increasing power density and cost) nickel–cadmium (NiCd), nickel–zinc (NiZn), nickel metal hydride (NiMH), and lithium-ion (Li-ion) cells. (wiki)
Unit Analysis • One of the most important things to do in manipulating equations involving physical entitites like power and energy (and everything is science) is unit analysis. • Unit analysis means putting the correct units of various quantities in your equations, and making sure that the unit type carried through the equation is correct.
Unit Analysis: An example • The watt (symbol: W) is a derived unit of power in the International System of Units (SI), named after the Scottish engineer James Watt (1736–1819) measures the rate of energy conversion or transfer. • One Watt is defined as one joule per second. • One watt is the rate at which work is done when one ampere (A) of current flows through an electrical potential difference of one volt (V). • Typical large power plants generate about 1000 megawatts. • In your electric bill you pay for kilowatt hours at a rate of about 5 cents per kilowatt-hour. • Given that watts is joules per second, and you pay for watts time hours, you pay for joules, or total energy.
Analog vs. Digital Circuits • Analog circuits usually have continuous values and are ‘analogs’ of what they control. For example, a knob varies a resistance which varies the current through a light bulb, dimming it. • Digital circuits implement Boolean logic functions with all or none states corresponding to 0 or 1. While there were once analog computers, now virtually all computers are digital, such as TTL and CMOS. • The interface between the world and digital circuits is done via analog to digital and digital to analog converters.
Devices for Analog Circuits • Analog circuits use: • Operational amplifiers (opamps, which are composed of transistors and resistors) • Transistors • Resistors • Capacitors • Inductors (rarely)
Transistor–transistor logic (TTL) • Transistor–transistor logic (TTL) is a class of digital circuits built from bipolar junction transistors (BJT) and resistors. • It is called transistor–transistor logic because both the logic gating function (e.g., AND) and the amplifying function are performed by transistors (contrast with RTL and DTL). • TTL is notable for being a widespread integrated circuit (IC) family used in many applications such as computers, industrial controls, test equipment and instrumentation, consumer electronics, synthesizers, etc. • The designation TTL is sometimes used to mean TTL-compatible logic levels, even when not associated directly with TTL integrated circuits, for example for the properties of the inputs and outputs of electronic instruments.
TTL Interface Properties • TTL is a current-sinking logic since a current must be drawn from inputs to bring them to a logic 0 level. • At low input voltage, the TTL input sources current which must be absorbed by the previous stage. The maximum value of this current is about 1.6 mA for a standard TTL gate. • The input source has to be low-resistive enough (< 500 Ω) so that the flowing current creates only a negligible voltage drop (< 0.8 V) across it, for the input to be considered as a logical "0". • If a TTL inputs is simply left floating it will provide a logical "1", though this usage is not recommended. • Standard TTL circuits operate with a 5-volt power supply. A TTL input signal is defined as "low" when between 0 V and 0.8 V with respect to the ground terminal, and "high" when between 2.2 V and 5 V.
CMOS • Complementary metal–oxide–semiconductor (CMOS) is a transistor technology for constructing integrated circuits. • CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits. • CMOS is also sometimes referred to as complementary-symmetry metal–oxide–semiconductor (or COS-MOS). The words "complementary-symmetry" refer to the fact that the typical digital design style with CMOS uses complementary and symmetrical pairs of p-type and n-typemetal oxide semiconductor field effect transistors (MOSFETs) for logic functions.
CMOS Characteristics • Two important characteristics of CMOS devices are high noise immunity and low static power consumption. • Since one transistor of the pair is always off, the series combination draws significant power only momentarily during switching between on and off states. • CMOS also allows a high density of logic functions on a chip, primarily for this reason that CMOS became the most used technology to be implemented in VLSI chips.