How to Choose the Right Resistor

« Back to Blog home pageEverything You Need to Know to Choose the Right Resistor for Your First PCB Design Project

Are you planning to start on your first PCB design? There are so many types of components that you’ll end up using, but none can beat the infamous of them all – the simple resistor. If you have ever looked at a circuit board, you’ll find resistors are all over the place, controlling the current flow and making those LEDs light up. But what exactly is a resistor, how does it work, and how in the world do you choose the right one for your first PCB design?

Fear not, we have you covered with everything you might need to know.

So…What is a Resistor?

Resistors are one of several passive electrical components, and what they do is relatively simple yet vital – creating resistance in the flow of an electric current. Have you ever seen a LED light up? That was made possible thanks to the trusty resistor. By placing a resistor behind a LED in a circuit, you get all of the brilliant lights without anything burning out!

The value of a resistor is its resistance, measured in Ohms (Ω).  If you have ever taken a basic electronics course, then your instructor likely drilled Ohm’s Law into your head. You will use Ohm’s Law time and time again when dealing with resistors. More to come on this:

Finding a resistor symbol on a schematic is easy. The international symbol is a standard rectangular shape, but the US standard has the zigzag line that makes it easy to identify. Regardless of the form, both styles have a set of terminals connecting the ends.

resistor-symbol

The resistor symbol in both US and International versions.

What Are the Different Types of Resistors?

There’s a ton of resistors floating about that are divided into two categories – construction type and resistance material. Let’s cover both:

Construction Type Fixed Resistors – As the name implies, these resistors have a fixed-resistance and tolerance regardless of any changes in external factors like temperature, light, etc. Variable Resistors – These parts have a modifiable resistance. The potentiometer is a great example, which has a dial that can be turned to ramp up or down the resistance. Other variable resistors include the trimpot and rheostat. Physical Quality Resistors – These resistors are like chameleons and can change their resistance based on a variety of physical properties, including temperature, light levels, and even magnetic fields. Physical quality resistors include the thermistor, photoresistor, varistor, and magneto-resistor. Resistance Material

Resistors can also be broken down into the actual material they are made from, which has a massive effect on how they resist current. These materials include:

Carbon composition Carbon film Metal film Thick and thin film Foil Wire Wound

Carbon composition is an older technique that has been around for a while and produces a resistor with a low degree of precision. You’ll still find these for use in applications where high energy pulses occur.

Of all the resistor material types, wire wounds are the oldest of them all, and you’ll still find these in use when you need

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