From the course: Electronics Foundations: Basic Circuits

Types of resistors

From the course: Electronics Foundations: Basic Circuits

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Types of resistors

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- [Instructor] Resistors are electronic components that have a specific amount of electrical resistance, and we can use resistors to control and direct the flow of electrons through circuits by limiting the amount of current that goes to certain parts of the circuit. The most common type of resistors are called static resistors because they have a constant amount of resistance. It may not always be possible to find a static resistor with the exact resistance value that you want for a circuit because they're only manufactured in certain standardized values. So you'll need to pick among the resistors that you do have available to get a close alternative. The list shown here contains some of the more commonly used resistor values. And as I build circuits throughout this course, I'll be choosing my parts from this list, which I've included in the exercise files for you to use as reference. Resistors are passive components, which means they cannot produce any electrical power on their own. They only consume power by converting electrical energy into heat. That means they need to be physically large enough to dissipate all that heat. The size of a resistor package will depend on its power rating, with larger resistors being able to handle and dissipate more power. Static resistors typically come in one of two physical packages: PTH, which stands for plated through-hole, or SMD, which stands for surface-mount device. Through-hole components usually come in a small tube shaped-package which has long metal leads that can be easily bent and inserted into a breadboard. I always keep a healthy supply of through-hole resistors on hand for prototyping circuits. Common through-hole resistors come in a range of different sizes with different power ratings. They can handle as little as 1/8 of a watt all the way up to two watts. There are also specially designed power resistors, which often have very small resistance values, but can handle tens or even up to hundreds of watts. Surface-mount or SMD are tiny little rectangular packages which are soldered onto printed circuit boards like this one. While there are several different sizes of SMD resistor packages, they're designed to be as small as possible, so they usually can't handle as much power as their larger through-hole counterparts. Surface-mount components are great for building compact electronic devices on printed circuit boards, but they don't work well for prototyping circuits with a breadboard. Through-hole components are often used to first build a prototype, and then they're replaced with surface-mount components when the design is turned into a finished product. When static resistors are represented in electronic schematics, they usually don't include information about the physical characteristics of the resistor like whether it's a through-hole or a surface-mount part, or how much power it can handle. Those details are left to other documents and are important to consider when actually building a circuit. In addition to the static resistors, there are also several types of variable resistors whose resistance can be adjusted through different types of interactions. Potentiometers are the most common type of variable resistor. They come in a variety of shapes and sizes. And in general, they're larger than static resistors because they contain movable components that are meant to be manually adjusted. They usually come as knobs or sliders and are used for tasks like adjusting the volume on a stereo. The schematic symbol for a potentiometer looks like a regular resistor with an arrow pointing at it from the side. Be careful not to confuse the symbol for a potentiometer with another type of variable resistor called a rheostat, whose schematic symbol looks like a resistor with an arrow crossing over it. The potentiometer has three terminals that operate as an adjustable voltage divider, whereas the rheostat only has two terminals and operates as a resistor with an adjustable value. I'll provide more details on how to use potentiometers and rheostats later in this course. There's another type of variable resistor called a photoresistor whose resistance changes based on the amount of light shining on it, which makes photoresistors useful for building light-activated switches and detector circuits. As the light shining on a photoresistor increases, it becomes more conductive and its resistance decreases. Photoresistors are represented in schematics with this symbol that includes two little arrows pointing at the resistor in a circuit. The actual photoresistor component looks like a flat disc with a metallic zigzag pattern on its surface.

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