A Place Where No Dreams Come True...

Current Topic: Understanding the difference in characteristics between components is extremely necessary to chose the best type for any given circuit. The reason there are numerous choices (within a component category) are that each type has been developed to meet a particular circuit need. A good designer should know this.

No Component Can Live Up To It's Theoretical Expectations...

For every type of electronic component there are multiple choices where each choice represents some kind of compromise. The key is to chose the type that does not compromise the important characteristics of the given circuit. Or at least minimize the effects (non desirable). In other words there is commonly not a perfect match and a 'best fit' must be chosen.

This is necessary because no component is perfect and they all suffer various effects that are a direct result of the materials they are comprised of. Although they 'all' will perform their basic function most 'high definition' (high fidelity) analog circuits have specific needs beyond basic functionality. Concerns being noise (consistency), response, impedance, usable bandwidth, power and even 'form factor'.

And for each new technology that developed, if it promised good growth, new components based on new materials became available. This was a very critical market, in the old days, fortunately. With few exceptions all the types of the discrete components to meet the needs of the common categories of electronic circuits have survived to this day. There are very few exceptions and arguably that is for a good reason. Mostly economic. Sadly.

Resistors...

The few resistor types that have existed for many decades seem to satisfy all electronic needs. Mostly... The differences have become a matter of debate which usually revolve around how electrons flow through the various materials used. Other then that it boils down to stability, or, how they 'drift' over time and with temperature and of course the type of noise (random molecular mobility) they contribute to a circuit. Generally these effects can be neglected however there still remain several applications where the choices made at design time can make or break a project when it leaves the lab and becomes a consumer product.

Carbon Composition: This is the original resistor type. They were used in the billions in every piece of tube equipment produced. Composition resistors are made by creating a solid resistive element using mixtures of carbon powder, ceramic powder and resin (binder) where the ratio of carbon to ceramic determines the resistance. They are inherently suitable for 'moderately' high-voltage and came in various sizes allowing use in medium-power circuitry. Unfortunately they weren't very precision. Basically... The values were chosen so that the resisters could be sorted, after manufacture, to fit within a 'standard' value and tolerance. Not exactly what you would call a precision process. They were also known to drift significantly with temperature but were relatively stable otherwise. These resistors have been superseded by Carbon-Film and have not been manufactured in decades. Except for 'New Old Stock' they are almost extinct.

Wirewound Resistors: This is the oldest type of resistor there is. Based on the natural resistive properties of metals and alloys the resistance is strictly determined by the length of the wire and it's known properties. This allowed for reasonably precision components and additionally wire size could be scaled to provide large power handling devices. But because they were large coils of wire they also suffered from inductance effects. In a serious way. Modern equivalents have managed, through creative winding techniques, to reduce this problem (non-inductive). None the less proper selection of this type can take advantage of these effects for the right circuits.

Film Resistors: This is where the industry transitioned to a precision manufacturing processes. There are many types, and grades, of film resistors. but they all have something very basic in common. Predictable behavior. for each type (Carbon, Metal, Oxide, Thick, Thin) the drift characteristics for time and temperature were extremely consistent and now measured in 'ppm' (Parts-Per-Million). Noise factors were also reduced and now extremely reliable.

Foil Resistors: These are the ultimate resistors. In every way. An observed property in a material originally designed as a strain-gauge for large Architectural buildings as a method for finding 'Weakness' exhibited almost ideal resistor potential. Further development led to the Metal-Foil Resistor. The metal foil, by far, exhibits the lowest and most consistent noise, extremely low drift over temperature and long term drift measured in ppm-per-decade (ten years). They also exhibit extremely low parasitic effects (inductance, capacitance) making them overall the most 'Linear' resistor.

Capacitors...

In the old days capacitors were big and bulky and contained many hazardous materials. That was necessary because most circuits relied on high voltages to pump the electrons and the materials available were not suitable dielectrics for small form factors. With the development of solid-state a whole new world opened up for capacitors. With more reasonable voltage limits many new types became available. All with very different characteristics designed for very specific applications while retaining the ability to work equally well in any 'Common' circuit.

Paper: This is the original 'General Purpose' Capacitor. The paper was saturated in oil and used as a dielectric. Wrapped with metal foils capacitors of various sizes and values could be mass produced. Originally there were few values over a wide range of capacitance and voltages. They had poor long term stability and didn't like moisture. It wasn't long however that new epoxies, high temperature materials and hermetic packaging made this type of 'Paper In Oil' capacitor a legend and still sought after.

Ceramic: This is an ancient type of capacitor having been adapted, through technology, to still remain a favorite choice for many circuit requirements. Originally dielectric layers of 'Porcelain' suspending electrodes of metal evolved into a single, relatively small, 'Ceramic' disc separating two electrodes. Adapted to the modern world ceramic capacitors are now made by layering ceramic and electrodes at a microscopic level. With very predictable characteristics and extremely high reliability.

Mica: Another original the mica capacitor uses a natural crystal 'Mica' as the dielectric. Original mica capacitors were horribly unstable over time. But like any good design new materials and creative manufacturing techniques have preserved this type as 'Dipped Silvered Mica'. Dipped (coated) in epoxy achieves a good hermetic seal and still allows for a very wide temperature operating range and very good long term stability. Generally available in precision values and moderately high voltages these remain a specialty choice when extended operating ranges are truly required.

Glass: The last original capacitor is glass. Real 'Fused-Silica' glass is the most stable dielectric over time and temperature and even various types of radiation. Because of those properties they are very well suited for medical and aerospace applications. However they still suffer from moderate parasitic influence.

Plastic: When it became available plastic quickly replaced paper as a dielectric. Plastics could be consistently manufactured with numerous properties and in previously unobtainable thicknesses. And since it was primarily a Solid State market the thin dielectrics were perfectly suitable for the low voltages now common. This gave rise to precision devices with vast values over huge ranges. Common types included Polystyrene, Polyester, Polycarbonate, Polypropylene, Polyethylene and a few more. Each with various parasitic effects with polystyrene being the lowest on the scale.

Teflon: Even though most people would lump 'Teflon' (very rare) in the Plastics category. This particular dielectric material jumps ahead of the rest. It exhibits the lowest amount of parasitic effects and the widest temperature operating range. For the most critical circuit types this capacitor is truly in a league of its own.

Aluminum: Blah blah!

Tantalum: Blah blah!

Inductors...

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Diodes...

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Transistors...

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Op Amps...

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Conclusion...

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