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 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.
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.
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.