All posts by etimaster

Potentiometers

Potentiometer
1M Potentiometer

pileofPotentiometer
Pile of Potentiometers

Potentiometers, often referred to as “pots”, and are considered to be a passive electronic component. They are, in fact, a type of resistor. To be more precise, they are really a three terminal variable resistor. Unlike a fixed resistor, that has a predetermined resistance, the potentiometer gives the user the ability to adjust the given resistance from essentially zero ohms (the measure of resistance) to a specified maximum value.

There are two different configurations of potentiometers that are used to adjust the resistance value. The most common of the two is the dial or rotary type potentiometer. The other, less commonly used, is the slide potentiometer. The dial type can be rotated 360 degrees. Both the slide and dial type are often used in audio receivers to vary the sound output.

Trimmer potentiometers or trim-pots, as they are commonly called, can be found in either the dial or slide configuration. These trimmers, as they are also frequently referred to, are used for infrequently adjusted calibration voltages. One of the common usages is in instrumentation where you make a voltage setting one time and leave it.

Potentiometers are rarely used to control significant power, but are used to adjust the level of analog signals. One application potentiometers are often used for is the dimmer switch on lights. Another is for the volume control in consumer electronics applications. As mentioned earlier, the potentiometer is not meant to handle a significant amount of power, that function is reserved for the rheostat, but that is a subject for another Hub Page.

Polycarbonate Capacitors

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Arizona Capacitors

Polycarbonate capacitors are a ttpe of wound film capacitor that have been around for a number of years. The film used was first introduced as a dielectric material in 1958, and it quickly became a favorite of designers and engineers in the instrumentation, filtering, and switching power supplies fields.

They are used in numerous applications, especially those that require precision performance in their systems and they are typically used in a -55 degrees Celsius to a +125 degrees Celsius environment. They are also a preferred choice for many applications because of their stability. They are classified as a precision capacitor because of these facts.

In the last few years, however, the film has stopped being manufactured and only those companies with an adequate inventory supply of polycarbonate film have been able to keep producing these types of capacitors. For example, Arizona Capacitors Inc., has approximately a fifteen year supply of the film and will be manufacturing polycarbonate capacitors well into the foreseeable future.

The long term future of polycarbonate capacitors is questionable and eventually another kind of capacitor will step up and take its place. However, for right now, if an engineer or buyer needs these type capacitors there are still some companies that can and will supply them.

RF Power Attenuators

RF
Res-net Microwave Power Attenuator

Attenuators are considered to be passive electronic components. They are used extensively in RF and microwave applications. As the name suggests, they are used to attenuate a RF or microwave signal. This means they reduce the amplitude of a signal without the distortion of the waveform and as these operate in higher frequency ranges their VSWR (voltage standing wave ratio) also becomes a factor.

In most instances, power attenuators can be identified as those that operate over a 100 watts. There are some that actually operate in the 1,000 to 2,000 watt range. They all have heat sinks to disipate the heat these wattages generate. The largest ones, 1,000 to 2,000 watts, also have fans to further help dissipate the heat that their extensive power creates. The attenuator in the picture to the right is a 1,000 watt attenuator that operates up to 2.4 GHz.

As we move away from analog signals in favor of digital because of its lack of noise, there is less power that is required. So, the need for these type of larger power attenuators in not as prevalent as it once was in the past. There are, however, still requirements that call for these power carrying components, albeit they are not as common as they once were.

SMT Resistors

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Tepro Surface Mount Resistors

SMT resistors or surface mount technology resistors are a type of passive electronic component. They are more precisely a low profile resistor that mounts directly to the printed circuit board (PCB) as opposed to a thru-hole resistor where the axial leads go through the board while the body of the resistors rests on top.  They are extremely useful and popular where space or PCB real estate is at a premium.

There are a number of different styles or types of SMT resistors. Chip resistors are common place in many mobile phones and other portable electronic devices where “the smaller the better” is the battle cry and board space is extremely valuable, but power requirements are very low. They can be either thick film or thin film, depending upon the application requirement. These resistors have the connectors or contacts directly on the resistors itself and are therefore soldered directly to the board.

Another type of SMT resistor has leads extending from its body and are bent in such a way that the resistor itself is flush with the PCB. These are called gull wings and they can achieve higher power levels than there SMT chip counterparts. There are some on the market that are rated as high as 35 watts. Beware, however, as many of the SMT resistors with higher power ratings stipulate a lower temperature or specify the type of mounting in order to dissipate the necessary heat.

Lastly, for our discussion, there is the disk resistor. It is cylindrical in nature and is used in high frequency applications. They are used in low inductance applications because their geometry does not create a magnetic field. These type resistors are more common in RF and microwave applications.

In this world of smaller and smaller mobile devices, SMT resistors will be with us for the foreseeable future. As the power requirements continue to be reduced, so will the size of these SMT resistors.

Medical Magnetics

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Winatic Medical Magnetics

Magnetics are classified as a passive electronic component and are comprised of either inductorscoils, or chokes. They are manufactured by winding a copper wire, called magnet wire, around some type of core. These core materials can be made of plastic, iron, or even air itself. The latter is called a self supporting coil or air coil.

These type components are used extensively in all types of medical equipment, from defibrillators to X-ray equipment. As you might imagine, the integrity of any component used in any type of medical device has to be flawless. So, for that reason high reliability components are required in the manufacture of these types of instruments.

All these parts used in medical applications need to be inspected 100%. Whereas, an AQL or sampling method may be adequate for consumer electronics, it will not be stringent enough for the medical equipment industry, where every application can be quite literally a life or death situation.

Winatic Corp. is a company that has been in the magnetics business for well over forty years and specializes in these type of high reliability components. They are currently working on their ISO 13485 certification which was specifically created for the medical device industry. They will be approved within the next twelve months.

There are many changes waiting in the wings for the medical industry that may or may not transpire. One thing that will not change, however, is the integrity of the machines that monitor our health and the reliability of the components within these devices.

Passive Electronic Components

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Variety of Film Caps by Arizona Capacitors

The term Passive electronic components is a broad category. They are used in all types of electronic circuitry, but are often overlooked in their importance to the operation of the circuit. The passive electronic component stands ready to perform in a circuit when provided an external voltage or current stimulus. The active component, on the other hand, is often part of the power supply providing the stimulus for the passive circuit. Semiconductors are probably the most commonly used active electronic component.

Passive components, like resistors and transformers, are often constructed using resistance wire for resistors and magnet wire for transformers. Various metal foils are often used in wound film capacitor construction.

Another construction method used for metal film resistors and tantalum capacitors is to deposit either metal or dielectric film using vacuum thin film sputtering techniques. Vacuum sputtering is a precise and accurate means of construction. No wire or foil windings are necessary with this type of resistor or capacitor construction.

When ceramic substrates are used and RF or microwave frequency performance is desired, thick film construction of the metal conductors becomes a cost effective method for products like attenuators and terminations.

Thin film construction, while more costly, provides the best performance for RF/microwave resistors since the thin film morphology can be made very homogeneous. The created homogeneous resistor surface then distributes the applied power very uniformly eliminating hot spots that can often lead to poor MTBF’s and early product failures. Since thin film resistors are created using optical masking techniques, very small and accurate resistors can be constructed.

Sputtering Techniques

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Sputtering Machine

There are essentially three different ways to sputter material onto a substrate. One is called Direct Current (DC) Sputtering, the second is called Radio Frequency (RF) Sputtering, and the third is referred to as Reactive Sputtering.

Sputtering is an arc process where there is a thin film that is deposited by etching a material from a source onto a substrate. The sputtered atoms are ejected from a target. It is often referred to as thin-film deposition. This process is used extensively in the manufacture of both active and passive electronic components.

Direct Current (DC) Sputtering is the simplest sputtering process. It cannot be used to deposit dielectric or inorganic materials like oxides, but it can be used to deposit almost any metallic material.

Radio Frequency (RF) Sputtering is more adaptable than DC Sputtering. It is not limited to electrically conductive targets like DC Sputtering. It can use targets such as silicon oxides and polymers.

These sputtering processes are commonly used to manufacture thin film resistors and rod resistors.Both of these resistors operate at the RF to microwave frequencies.

The Reactive Sputtering is the most complex of the three processes and is where a reactive gas is used along with inert argon to form a plasma. The reactive gas becomes activated and chemically combines with target atoms to form a compound. Two widely used reactive gases are oxygen and nitrogen. This process is used widely for the deposition of dielectrics, resistors, and semiconductors.

Three Types of Capacitors

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Various Types of Caps by Arizona Capacitors

Capacitors fall into a category of electronics called passive electronic components and they are the second most common component in the average circuit, next to resistors. There are various types of capacitors available to the design engineer, depending upon what he needs.

There are three different types or families of capacitors that will be discussed in this Hub; wound film capacitors, tantalum & electrolytic capacitors, and ultra-capacitors. Only the first one of these is wound. All of the others are manufactured by laying down a film via sputtering or some other method. Whereas, the wound film capacitor is produced via winding a metal film onto a core, as the name implies.

The tantalum and electrolytic capacitors have their own niches, such as higher frequency applications. The wound film capacitor, on the other hand, has been the workhorse for the electronics industry for a number of years, this is because, in no small part, of its reliability. There are a number of different types of wound film capacitors. These are mostly categorized by the type of film they are wound upon.

There are many wound film capacitors. The polycarbonate capacitor is a typical example of a wound film capacitor. It is often used in the instrumentation, filtering, and switching power supplies fields. They are also preferred for many applications because of their precision and stability.

The tantalum capacitor is a typical electrolytic capacitor. It is one that is used extensively in audio applications. It is manufactured from a tantalum powder. The dielectric is thin making a high capacitance achievable with a relatively small size, but they can also be more expensive as well. The electrolytic capacitor is one that used an electrolyte as one of its plates. They are able to create the highest capacitance’s of any capacitors. The other type of electrolytic capacitor is aluminium.

Lastly, we have the ultra-capacitor or super-capacitor. It is an electromechanical capacitor that has a high density level. They are also know as electric double layered capacitors (EDLC) and they can have capacitance up to 5,000 farads. They do not have the dielectric found in most other capacitors, but have a double layer of separation giving them a rating for higher voltages than the other more common types of capacitors.

Rod Resistors

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Res-net Microwave Rod Resistors

Rod resistors are a cylindrical type resistor that are used in both RF and microwave applications. They are thin film in nature and can be made of alumina, beryllium oxide, or aluminum nitride.

Because of their thin film construction they can achieve very high frequencies. These frequencies can be as high as 26.5 GHz or even higher in certain applications. Res-net Microwave Inc. is one of the few companies that offer rod resistors in alumina, beryllium oxide, and aluminum nitride materials.

The resistance range for rod resistors is generally from 10 ohms up to 500 ohms, and the resistive tolerances are generally 1%, 2%, or 5%. The temperature range is -65 Degrees Celsius to +175 Degrees Celsius. The resistors are covered with a protective coating of high temperature epoxy in order to insulate them from these temperature extremes.

In addition to these classic thin film rod resistors, they can also be supplied using pyrolytic carbon. These carbon rod resistors also perform very well at microwave frequencies and have the added advantage of being able to work to the temperature of +200 Degrees Celsius. The sizes of the carbon resistors mimic those for the other thin film types. These carbon rod resistors will have a negative temperature coefficient as compared to the other resistors which will have either a plus or minus 100 ppm TC.

The power ratings can go from 0.050 watts all the way up to 75 watts, depending upon the material used. They are used extensively in the RF and microwave industries especially in the manufacture of other components such as, SMA terminations.

Carbon Film Resistors

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Vamistor Carbon Film Resistors
Source: Tepro of Florida, Inc.

Carbon film resistors are designed for both high temperature and high voltage applications. They are actually made in a vacuum by breaking down hydrocarbon gases at high temperatures. This in turn forms a carbon deposit on the substrate. The process is accomplished by heating methane or propane gas in a process called high temperature pyrolysis. When the heat is applied, molecular condensation results and hydrogen is released. The end result is carbon.

The main advantage and reason for using the carbon film resistor is that these components are designed to withstand high voltages as well as high temperatures. The highest voltage the devices can operate up to is 15kV with a nominal temperature of 350°C. They are available with tolerances of 2 percent, 5 percent, 10 percent, and 20 percent. Cutting a helical grove in the carbon film creates the resistive tolerances. The desired resistance value is achieved by regulating the pitch of the helix. The thinner the carbon layer, the finer the pitch and the higher the resistance value. After the helixing or spiraling is completed special alloy contact caps and tinned electrolytic copper connecting wires are pressed onto the ends of the resistor body. The final step involves coating several layers of tan lacquer or using a glass film as a shield. This is done primarily for electrical protection, but also for shielding from the climate.

Carbon film resistors are a good choice because they have a small size for such high ratings and they have a wide resistance range as well. The resistance can be anywhere from 500 Ohms to 100M Ohms. Another plus is that they have no outgassing. This means they will not deposit any vapor into the environment during operation. Outgassing is a condition that causes high material vapor pressure in the device to emit contamination deposits into the air. It corresponds directly to the temperature.

These deposits can cause problems with the surrounding equipment. Some of the other advantages are that they have less stray capacitance and inductance, so they are better at high frequencies. Also, they have a high stability of performance when compared to carbon composition resistors and, of course, they are flame proof.

Electrical noise is another factor when choosing a resistor. There are two main types of electrical noise, thermal and shot. Thermal noise is the product of the Brownian motion of ionized molecules. This noise cannot be eliminated because it is fundamental to resistance.

Carbon film resistors have less of this thermal noise than the carbon composition resistor. The lower values tend to be noise free while increasing with the higher values. Shot noise usually results from the flow of electrons through a highly charged field. It is more prevalent in solid state devices. It is not significant in carbon film resistors and until recently was not even known to exist, with respect to resistors.

There are also some disadvantages when using carbon film resistors. In the first place, they are limited to about 1 percent accuracy. Secondly, they exhibit drift with temperature and vibration. The resistors can have a TCR (temperature coefficient of resistance) range of -250 to -1000 ppm/°C, depending on the resistance value. The advantages, however, seem to outweigh most of the disadvantages, especially in specific applications.