How To Choose the Right Resistor(s) for Your Project | Quest Components

26 Sep, 2019 | Quest Components
Variety of resistor types

How to Choose the Right Resistor(s) for Your Project

Resistors are among the most common of all electronic components, but not all resistors are the same. Resistors are made of different materials and come in different types. Each has unique properties that makes it better suited for specific applications and less than ideal for other applications. Here is what you need to know to choose the right resistor(s) for your project.



Resistance

The basic criterion for selecting your resistor is its resistance value. Resistors are sold in standardized value ranges set by the IEC (International Electrotechnical Commission). The values in each range follow an exponential curve, keeping the tolerance within a designated percentage. Custom resistance values are available, but they are special order items. Let us know if you have any unusual resistance values you need and we can provide with a quote for supplying the parts you need.

Tolerance

Tolerance is the amount that the resistance of a specified resistor can vary from its target value. Most resistors have a 5% tolerance, though 1% tolerances are readily available. Large “power” resistors tend to have a tolerance of 10% or even 20%, though precision models are available. High-precision resistors, with tolerances of 0.1% to 0.01% and lower are available, but tend to be a little more pricey when compared to the basic 5% resistor. The resistors with high-precision tolerances are highly useful for instrumentation, precision measuring devices, and reference applications to name a few.

Package and Mounting

Resistors are packaged in different ways and have different mounting styles. For one-off, hand-soldered applications, this is not necessarily a big concern. If you are mass producing computer chips, the packaging and mounting style could become a primary consideration.

Some common packages are:

  • Axial leaded
  • Surface mount
    • 0201
    • 0402
    • 0603
    • 0805
  • Radial leaded
  • Wire mounted

Power Dissipation Rating

Since the function of a resistor is to impede current flow, some power is dissipated as heat. Whether this matters depends on the size of the resistor, the size of the device in which it is placed, and the heat tolerance of the device. A tiny single resistor in an analog device is unlikely to dissipate enough power to be noticeable, while a bank of large resistors working at their maximum capacity can put out significant heat.

Voltage Rating

In physically small devices, the voltage ratings tend to be low. In large, high voltage systems, it is generally better and safer to raise the voltage of the circuit by connecting multiple resistors in series rather than using a single resistor at its max voltage rating.

Resistive Material

Not counting semiconductors, there are three basic types of resistive materials: composition, metal film, and wire-wound. Each has its own unique properties:

Film Resistors are made of conductive metal oxide paste on a ceramic substrate, and are laser cut to create tight tolerances. Due to their low noise and temperature stability, film resistors are ideal for radio frequency or high frequency applications.

Some common types of film resistors are

Wire-wound resistors are made by winding a wire of thin metal alloy onto an insulating ceramic. With high power ratings and precision low ohmic value, these resistors are a great choice for measuring circuits and heat sinks. In addition to resistance, some also have inductance, producing a combination effect known as impedance.

Some common types of wire wound resistors are

Composition resistors are made of graphite or carbon dust bound to non-conductive ceramic clay. They are inexpensive, low- to medium-power, low-inductance, and good for a variety of applications. However, noise and stability become problematic when these resistors get hot.

Some common types of composition resistors are

Temperature Range

In normal ambient temperatures, checking the power dissipation of the resistor is fine. If the resistor will operate in significantly elevated temperatures, though, it is important to look at the power dissipation derating curve. As the resistor gets closer to its maximum allowable temperature, the less power can be dissipated. This puts the resistor, and ultimate the entire device, at risk for overheating and failure.

Noise

Resistors can put out three types of noise: shot noise, flicker noise, and thermal noise. Shot noise sounds something like a rushing river, but it is generally an extremely low level of not-unpleasant white noise. Flicker noise is more random and can be far more annoying. Composition resistors have the most flicker noise, and larger resistors have less than smaller ones of the same type. Thermal noise becomes a problem at higher temperatures, and metal film resistors tend to have the least. Overall, lower-value resistors create less noise than higher-value resistors.

Choosing just the right resistor(s) for your project can be complex. It is best to work with a professional who can provide the guidance you need to ensure that you truly get what you need.

Ready to Get Started?

Here at Quest Components, we are committed to providing you with the information you need to help your business continue to run smoothly. An ISO 9001:2015 Certified Company headquartered in Industry, CA, Quest Components specializes in passive and active board level components. We also provide a variety of services to OEMs (original equipment manufacturers) and CEMs (contract electronics manufacturers) across the globe. Contact Quest Components today at 626-333-5858 for all your electronic component needs!

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