A WIZARD'S ELECTRONICS COMPANION

COMPONENTS

These are general descriptions of the "atoms" of our circuits. There are times when we must look beyond our lumped component effects, but we generally assume (and hope) the important things are occurring in the parts themselves. I will detail measurements of their operation in the Circuits section.

DISCRETE COMPONENTS

This refers to electronic components which have single, limited functions, such as a resistor, capacitor, inductor, transistor, etc., as contrasted with integrated circuits.

Conductors

Wire

In electronics terms, any conductor connecting two components, usually with an insulating layer molded over it for convenience. Electrons will stay in the conducting path unless the voltage on the wire rises so high (electrical pressure concept) that arcing and corona effects begin to occur as electrons fly off every which way, necessitating better insulation. Man-made equipment uses connections just atoms wide, all the way up to cables that are inches in diameter. Gold has about the lowest resistance, and it doesn't corrode, a good choice for plating electronic components made of copper, which does tarnish. Until we have one-size-fits-all superconducting wire, it will come in various sizes of stranded-copper, most commonly. It has a resistance, but what is more useful to know is how much current we can push through it without excessive heating. As a rough rule, #22 AWG (American Wire Gauge) should not see more than 5A. #18 should be roughly 10A. As a rule, the current-carrying capacity of wire can be calculated at changing by roughly a factor of two for every four gauge numbers. This is a bit lower when you get into big, thick cables that can't dissipate their heat as rapidly. The point at which the wire melts and fuses is much higher, of course.

Fuse

A component designed specifically to melt and break the conducting path in a circuit (an OPEN CIRCUIT results.) They are rated primarily for their fusing current, and secondarily for voltage, which is their ability to successfully break a circuit without a continuous arc forming and keeping current in the circuit flowing.

Circuit Breaker

Basically a re-settable fuse. A bi-metal strip inside heats and curls away from the connection point, breaking the circuit. Also rated for current and voltage. (Note: the DC current rating will be lower than an AC current rating because in AC, the current and voltage in an arc will go to zero for an instant as the electron flow reverses, making it much easier to break the circuit.) A thermostat is a version of this with a long, coiled bi-metal strip which is exposed to ambient air temperature. The current through this strip is small and constant, and is not intended to provide the heat for the bi-metal strip, but to power a control relay.

Switch

A componet which allows one to safely and conveniently open or close the circuit as many times as one wishes. They come in a great many types. One should choose a switch which can handle the current in your circuit easily. In some circuits the current when the switch is first closed will be much higher than the normal operating current due to energy being stored in capacitors, and some circuits have a tendency to arc the switch when opening due energy stored in inductors being dissipated. These factors can greatly reduce the life of a switch if ignored.

Power Sources

Battery

An arbitrary array of chemical cells composed of a conductive liquid, certain salts, and chemically dissimilar metal plates for storing electrical energy in chemical form. There will be a DC VOLTAGE difference between the plates, typically a volt or two. If a wire (or other load) is connected to the plates outside the cell, DIRECT CURRENT (DC) will flow through the wire connected to the plates outside the cell, while chemical ions are flowing between the plates in the cell. This creates a CLOSED CIRCUIT. Eventually, one of the plates will have traveled, ion-by-ion, through the solution, and the useable cell energy will be exhausted. The EQUIVALENT CIRCUIT of a battery can be modeled by drawing an internal resistor inside the battery, and in SERIES with it (normally, this is not drawn, but is simply understood as an important feature of a battery.) If you SHORT-CIRCUIT a battery, it can get hot or even explode. We say that the heating is due to the INTERNAL RESISTANCE of the battery. This can even be crudely measured (remember, these are only models of reality) by putting a known load resistor across the battery and measuring the voltage lost in that internal resistance. Usually, one checks a pocket reference for the rating of a certain type of battery (in Amp-hours or milliamp-hours) to see if it fits your application.

AC Line Power

This is another way of describing the AC power from your local power company, typically 120V AC, 60Hz, at up to 20A (before the circuit-breaker kicks the power off.) The AC line contains an AC VOLTAGE which tends to create an AC CURRENT in a load.

Power Supply

A circuit (can be considered a component of a larger system) designed to take power from the AC line or battery and change it to one or more DC voltages and DC currents, or create different AC voltages, AC currents, and frequencies. Some such circuits will eventually be detailed in the later section.

Solar Cell

A TRANSDUCER (changes energy from one form to another) which converts the photon energy of sunlight into electron flow. A silicon solar cell generates about one-half volt. The current capacity is dependent on the area of the cell(s) and the efficiency of the conversion.

Passive Components

Resistor

Impedes electron flow, dissipating energy as heat in the resistor. No storage of electricity occurs. Ohm's Law, I = E / R, is the single most important formula in electronics because it describes the relation of the three most important units in one simple formula. Power dissipation can then be calculated with the help of P = I * E. Example: The RESISTANCE (in Ohms) of the resistor is labelled as 1000 Ohms (1k). (Ohms is written as a Greek omega, but most fonts don't have that as a character, so we'll write it or leave it out.) The VOLTAGE (in Volts) across the resistor = 9 V since it is connected directly to the battery on both ends (analogous to height of water column; one archaic term for voltage is electrical pressure). The CURRENT (in Amperes) through the resistor is equal to I = E / R = 9 Volts / 1000 Ohms = 9V / 1k = 0.009 Amps = 9 milli-Amperes = 9 mA (analogous to water current, or X-gallons of water flowing past a point in one second.) The POWER (in Watts) dissipated by the resistor as heat is P = I * E = (9 mA) * (9 V) = 81 milli-Watts = .081 W (water absorbs the heat of its falling pretty easily, but it's there.) The QUANTITY OF CHARGE (in Coulombs) that flows through the resistor in one second is Q = I * t = (9 mA) * (1 sec) (analogous to the amount of water.) The WORK done on the resistor in 3 seconds is W = I * t = (.009 A)(3 sec) = .027 Joules = 27 mJ

Capacitor

Stores electrons in a static charge. The capacitor is composed of two plates separated by an insulator. This structure can be rolled into a cylinder or created as two sets of interleaved plates. When power is first applied across the capacitor, it acts like a short circuit for an instant. Maximum current will flow, and no voltage will be seen across it. Depending on the capacity, voltage will rise in the capacitor slowly or quickly, like filling a barrel full of water. Eventually, the highest safe voltage the capacitor was designed to hold will be seen across it. It could be disconnected from the circuit and the energy will still be stored statically in the capacitor. If the capacitor is allowed to form a complete circuit between its plates, as much current will flow as you allow, just like opening the bottom of a barrel. The voltage across the capacitor will drop according to how much charge remains. Unlike a coil, there is (usually) relatively little resistance in capacitors. Unless you use your capacitors in high-current applications, heat is not a problem. However, in higher-frequency applications, there may be an annoying amount of inductance. When DC pours into a capacitor, it will simply fill with a static charge to whatever potential you pump into it. It is somewhat permeable to the inrush and ebb of AC, however. For how permeable, I first turn to X[C] = 2 * pi * f * C if there is some dominant frequency you believe the capacitor is seeing. For a step-pulse (shift in DC level), I get a rough idea from t = R * C, where are is an external resistor feeding the capacitor (see Circuits: resistor and capacitor) to get a rough idea what my TIME-CONSTANT is for the RC circuit.

Inductor

Stores moving charge as a magnetic field. While each individual moving charge displays a magnetic field, the inductor concentrates this effect to create a kind of electrical momentum in a single device. The inductor is composed of any number of turns of wire around air or some other material as a core to multiply the effect of many charges moving in unison. Core materials like iron increase the effect significantly over that of air. When a power source is first applied to an inductor, it acts like an open circuit for an instant and no current flows initially. Current increases in the inductor at a rate proportional to both the applied voltage and the inductance. In a perfect inductor made of superconducting wire, this current would have no upper limit, but the resistance of the wire is the limiting factor in a common inductor. Eventually, the inductive reactance is overcome and the entire voltage is being dropped across the internal resistance of the coil. At this point the storage capability of the inductor has reached its limit, and there is constant loss in the internal resistance to the moving charges. If the voltage source is suddenly removed, the magnetic field begins to collapse, converting the electrical momentum back into current flow, attempting to keep the charges moving in the same direction at the same current. If the circuit has been opened suddenly, the voltage generated by the collapsing magnetic field in the coil will continue to rise until arcing occurs across the switch, somewhat like water crashing into a sea wall and sending water high up over the wall momentarily. DC currents can utilize a solid iron core to good effect, but AC currents allow transformer action to induce eddy currents in any electrically conductive core material. At low frequencies, such as the 60Hz line, a core can be whole steel plates which are electrically insulated from one another. At higher frequencies, core iron and other materials are finely divided and electrically insulated from one another in a nonconducting resin to form a material called ferrite to reduce eddy current losses. When I work with an inductor in a noncritical application, I ask myself first if there is an overriding or primary frequency to the power being supplied to it, an AC signal, or perhaps simply a pulse repetition rate. I do this so I might use the formula X[L] = 2 * pi * f * L to obtain a rough idea of the inductive reactance this device will likely be producing. If not, or if there is an obvious STEP-PULSE (a DC level which suddenly shifts), I resort to t = L / R, where R is an external resistor feeding the inductor (see Circuits: resistor and inductor) to get a rough idea what my TIME-CONSTANT is for the RL circuit.

Transformer

Two inductors "joined at the hip" so they share a common core. Since the energy is stored as a magnetic field, it is accessible to both coils, no matter which coil it originally came from. Since inductors have to have current forced into them to affect their magnetic fields, transformers work only with AC or pulsed DC currents. They are used most often to DC-isolate the PRIMARY winding (where power is put in) from the SECONDARY winding (where power is output from the transformer) while changing the voltage output to a more desireable value. The ratio of AC voltage secondary / primary is in the same ratio as the number of turns of wire wound around the core for each. The ratio of currents between secondary and primary is just the opposite so that the total power available from the transformer will remain constant. Substituting P = I * E in an ideal transformer, P[pri] = P[sec], or I[pri] * E[pri] = I[sec] * E[sec]. And their relationship to the ratio of the numbers of wire turns around the core: E[pri] * N[sec] = E[sec] * N[pri].

Transducers

Solenoid

Another variant on the inductor. This one has built-in resistance. This is an inductor which uses the magnetic field it creates when you pass a current through the coil to pull a piece of ferrous (iron-bearing) metal, converting electricity to a simple physical movement of typicall a centimeter or less. A spring is built into the mechanism to push the iron or steel slug back out when the circuit is broken. Unlike a typical inductor, solenoids, relays, and contactors usually have enough coil resistance so that a DC voltage can be applied directly to it for indefinite periods of time (some are underdesigned for intermittent use only.)

Relay

A solenoid with electrical contacts attached so that it acts as a switch.

Contactor

A heavy-duty relay.

Electromagnet

Another inductor variant which uses the magnetic field created when a DC current is passed through the coil to lift iron and steel

Microphone

Conversion of sound-pressure waves into electrical-pressure waves -- an audio SIGNAL.

Speaker

The opposite of the microphone, converting an electrical signal into acoustic pressure-waves.

Motors and Generators

These are related since not only does a magnet moving past a wire cause electrons to flow in the wire, but electrons flowing in a wire will generate a magnetic field and push (or pull) on a magnet. This is a very complex field, but the basic idea is to get two magnets to pull / push on one another to generate a forceful spinning action (in a motor), or use a spinning action to generate a forceful flow of electrons (in a generator). The magnets can be either a permanent one against an electromagnet which alternately changes its POLARITY (direction of its current / charge / voltage / magnetic field), or an INDUCTION MOTOR which uses two electromagnets.

Incadescent Lamps

The classic lamp of Thomas Edison. A metal filament of tungsten (highest melting point) is placed in a glass bulb and all the air is sucked out. When current is passing through the filament causes it to become white hot, the lack of air prevents the filament from burning. These are slowly going the way of the dinosaur for use as light sources and indicator lamps for many applications now that ligh-emitting-diodes and fluorescent lamps have increased in efficiency.

Gas-Filled Lamps And Fluorescent Lights

If a gas is put into a glass bulb, a high-voltage across two electrodes immersed in the gas will cause the gas to ionize, and releasing photons. A neon bulb works on this principle with its characteristic weak orange glow. Sometimes more energy can be released invisibly, such as ultraviolet. If the inside of the glass bulb is coated with a fluorescent substance, the ultraviolet will be absorbed and visible light will be released.

Light-Emitting Diode (LED), Photodiode, and Phototransistor

It was discovered that current flowing through certain semiconductor junctions gave off light, and some were likewise able to convert light into a current flow. LEDs are sold as indicator lamps and are now being developed for flashlights and other lighting applications because of their high efficiency, lower heat output, long life, and sturdy construction. Photodiodes and phototransistors have been optimized to be sensitive to incoming light. There have been instances where circuits exhibited anomalous behavior due to ambient light not sufficiently blocked from getting to semiconductor material in components.

Piezoelectric Devices

These are crystals which bend under the influence of a voltage placed across them. If the voltage is AC, the crystal will vibrate creating an audible tone. Likewise, devices have been developed to use the reverse effect. There is a plastic sheet material with metallized surfaces which generate a voltage when bent, useful for keyboards, for example. The heart of a computer CPU clock is a crystal, where a small AC signal is applied and the crystal is allowed to vibrate at its natural, resonant frequency.

Thermistor

This is a resistor whose resistance depends on the temperature. Useful for simple thermometers.

Thermocouple

When two different metals are touching, and that junction becomes warmer or colder than the rest of that dissimilar wire in the circuit, a small current will be produced. This is used particularly for thermometers, though if enough thermocouples are heated, enough electricity can be generated for radios and such.

Discrete Semiconductors

DIODES

Diode

Generally refers to a PN diode, composed of a layer of P-type and a layer of N-type silicon semiconductor material, which when brought together will exhibit nonlinear resistance at different voltages. When positive voltage is applied to the P material relative to the N, very little current will flow until nearly 0.7 volts is reached. The resistance will decrease (and the current will increase) logarithmically with increasing voltage (usually not above a volt or so before the current will be so high it burns-up), but it will look like an open circuit if the voltage on the P material is more negative than the N. It will block nearly all reverse current until the device's breakdown voltage is reached.

Zener Diode

Has the same blocking properties as a regular diode, but is designed to break down at a low voltage in the reverse direction non-destructively (if the current is limited.) The breakdown voltage holds fairly constant over a wide range of currents. This is a useful feature for DC voltage regulation.

Varactor Diode

One of the more obscure properties of a diode is when you reverse-bias the semiconductor junction of P- and N-type material, the average distance between the positive and negative charges changes with applied voltage. Since no device is perfect, there is some capacitance in that juction. Well, capacitance depends on the area of the conductors, the insulating material (DIELECTRIC), and the distance between the plates. So, it acts just like a voltage-variable capacitor. One of the most common uses for these became TV tuners for changing the channel, eliminating a mechanical multi-position switch and fixed capacitors. It saves money, is less noisey electrically, and is more reliable.

Schottky Diode

This is noted for its lower voltage drop when forward-biased, typically around a quarter volt, and that it turns on and off very fast.

Tunnel Diode

This diode will begin increasing current with increasing voltage when forward-biased, just like a regular diode, but at some point the current will begin to decrease over a range of voltage, then begin increasing again! This NEGATIVE RESISTANCE section in the middle can be used to make an amplifier. It is mostly used in very high frequency circuits.

SCR, DIAC, and TRIAC

These geometries produce yet more odd behavior to applied voltage. The DIAC will block current in both directions until a break-over voltage is reached in either direction where current will conduct heavily. If the current is externally reduced below a certain level, the device will switch off again. The TRIAC is like a DIAC with a control gate. The device is switched on to conduct heavily either way (symbol is two diodes in parallel with a control lead) by applying a voltage to the gate, and can only be switched off by reducing the current in the main channel below a holding current threshold. The SCR is just like one-half of a TRIAC in that it is designed to conduct heavily in only one direction and block current in the other. That is why its symbol is a diode with a gate lead.

Light-Emitting Diode

A junction diode whose properties allow it to give-off light when current is flowing. (Described in transducers section.)

TRANSISTORS

JFET

Here again is a device designed to use a PN-junction that is reverse-biased. A channel of one type of material (P- or N-type) is formed between two leads as a conducting channel. The other type of material is formed into a control gate attached to a third lead. If a voltage is applied between this GATE and one of the other two leads (we designate it the source which reverse-biases the PN-junction, the electrostatic repulsion of the charges form a barrier to conduction through the channel between drain and source. It is particularly useful as a high impedence input to a circuit.

MOSFET

This is similar to the JFET except there is a glass barrier between the two P and N materials. Even higher impedence than a JFET. Glass is an excellent insulator, but it has a high DIELECTRIC CONSTANT, which increases the capacitance between the gate and both the drain and source. As the frequency of the signal increases into the MOSFET, more and more current has to be pumped into and out of its input capacitance in order to turn it on and off, with peak currents approaching 100mA, even though at DC the current may be as low as 10^-16 A. This tends to be true of CMOS ICs, as well, because of their similar construction.

Bipolar Transistor

A three-lead device which uses two leads for biasing the ON resistance of another pair of the leads. The third lead, which is common to both pairs, gives rise to the naming convention for the three basic configurations: common-emitter, common-base, common-collector. The two types of bipolar transistors are NPN and PNP. The doping of N- or P-type material alters the ability for charges to move, creating regions which are more, or less, resistive near the interfaces between these materials. The P in NPN (and N in PNP) is a very, very thin layer separating the two N-layers (or two P-layers) and is attached to the base lead. The other two leads are the collector lead and the emitter lead. All transistors are really voltage-controlled devices, but it is sometimes useful to think of them as current-controlled. When a small voltage (0.7V) is applied between base and emitter of an NPN transistor, the resistance of the collector-to-emitter junction drops from megohms to ohms. Typically the collector has a more positive voltage than the emitter as well. PNP polarities use voltages on the base and collector which are more negative than the emitter. See Bill Beatty's in-depth viewpoint on the Amateur Scientist for How do Transistors Work?.

Programmable Unijunction Transistor (PUT)

This is a small, three-lead device which uses two leads for biasing the turn-on threshold and one for both turn-on gating and conduction of current (which exits on one of the other two leads.) Typically, the gate electrode has a capacitor attached which charges up to the threshold. At turn-on, resistance drops very low suddenly, and the charge is dumped rapidly through the device at a high current.

INTEGRATED CIRCUIT (IC)

Analog IC's

OPERATIONAL AMPLIFIERS (OP-AMPS)

Both a circuit (or most of one), and a functional block, these are amplifiers distinguished by their extremely high voltage and current gains (1000 to 100,000, typically). Most are for low power applications (milliwatts).

DIGITAL INTEGRATED CIRCUITS

Digital IC's

Hybrid IC's

This is a class of integrated circuits that can include IC's which must be assembled as though one were building a circuit with discrete components, rather than an automated process. It can also refer to IC's which include both analog and digital circuitry.

ANALOG-TO-DIGITAL (A/D) AND D/A CONVERTERS

An A/D take an analog signal and converts it into a series of binary numbers.