How to Select a Resistor

When I was working on the next version of Common Parts Library, I realized that it would be helpful to explain why you might pick one type of passive component over another. We started off by writing “How to Select a Capacitor” last month, and are following it up with a close look at resistors this month.

In this blog, we will explain all the different types of resistors, their merits and demerits, and popular applications. We have included some recommendations for commonly used resistor series with high supply chain availability from the Common Parts Library and Seeed Studio’s Open Parts Library, and have linked to pre-created search on Octopart.

Let’s dive into the world of resistors:

Resistors resistors r3 r4

Resistors are two-terminal components used for limiting current, voltage division, and timing applications. Resistors complement ‘active’ components like op-amps, micro-controllers, or integrated circuits for variety of operations like biasing, filtering, and pulling up I/O lines. Variable resistors can be used to change the properties of a circuit. Current sensing resistors are  used to measure the current in a circuit. The unit of resistance is Ohms (Ω).

TYPES
There are several different types of resistors which differ by power rating, size, performance, and cost. Below are some of the common resistor types: chip SMD resistors, through-hole resistors, wirewound resistors, current sense resistors, thermistors, and potentiometers. We’ve also included their characteristics, applications, package information as well as info on part selection.

I. Chip SMD Resistors resistors

Chip surface-mount resistors provide a size advantage over through-hole resistors, so they are great for printed circuit boards (PCBs). Some of their common applications are pull-up/pull-down operations to ensure a signal is at valid logic level when external devices are removed, voltage divisions, current limiting, and filtering signals at certain frequencies in high-pass/low-pass/band-pass filters. You can use 0Ω resistors as jumpers to disable a sub-section of a circuit.

There are two kinds of Chip SMD Resistors:
1. Thin Film resistors are used in high precision applications like audio, medical, or test equipment. They have lower variation (0.1%-2%), a lower temperature coefficient (5 ppm/K), and are less noisy compared to thick film resistors. However, they are more expensive.
2. Thick Film resistors are the most common type of resistor, and are used for most applications. They have higher variation (1%-5%), a higher temperature coefficient (50 ppm/K), and are noisier than thin film resistors. If there are no specific performance requirements, thick film resistors are usually the preferred choice.

Package: 0201, 0402, 0603, 0805, and 1206 packages are the most common. The numbers represent the dimensions in the imperial system, with 0402 being 0.04 X 0.02 inches and 0603 being 0.06 X 0.03 inches and so on.

Part Selection:

0402 Yageo’s RC0402FR series for 0Ω to 10MΩ rated at 0.063 W (1/16 W)
0603 Yageo’s RC0603FR series for 0Ω to 10MΩ rated at 0.1 W (1/10 W) [CPL]
0805 Yageo’s RC0805FR series for 0Ω to 10MΩ rated at 0.125W (1/8 W)
1206 Yageo’s RC1206FR series for 0Ω to 10MΩ rated at 0.25W (1/4 W)
or

0402 Panasonic’s ERJ-2RK series for 10Ω to 1MΩ rated at 0.063 W (1/16 W)
0603 Panasonic’s ERJ-3EK series for 10Ω to 2.2MΩ rated at 0.1 W (1/10 W) [CPL]
0805 Panasonic’s ERJ-6EN series for 10Ω to 2.2MΩ rated at 0.125W (1/8 W)
1206 Panasonic’s ERJ-8EN series for 10Ω to 2.2MΩ rated at 0.25W (1/4 W)
or

0402 Vishay’s CRCW0402 series for 0Ω to 10MΩ rated at 0.063 W (1/16 W)
0603 Vishay’s CRCW0603 series for 0Ω to 470MΩ rated at 0.1 W (1/10 W) [CPL]
0805 Vishay’s CRCW0805 series for 0Ω to 470MΩ rated at 0.125W (1/8 W)
1206 Vishay’s CRCW1206 series for 0Ω to 470MΩrated at 0.25W (1/4 W)

II. Through-Hole Resistors resistorr3

Through-Hole resistors in axial leaded packages are popular and widely used esp. while prototyping as they are easily replaceable and can be used with breadboards. They are used for pull-up/pull-down, voltage division, current limiting, and filtering like chip SMD resistors. There are various types of through-hole resistors. Carbon film and metal film are the most popular.

Carbon film resistors have more variation in resistance value (2%-10%). They are most commonly available in E12 (± 10%), E24 (± 5%), and E48 (±2%) packages. Most applications have replaced carbon film resistors with metal film resistors. Carbon film resistors’ temperature coefficient (TC) is usually negative — around -500ppm/K — but the exact value depends on the value of resistance and dimension.

Metal film resistors have less variation in resistance value (0.1%-2%) and have higher stability. They are most commonly available in E48 (±2%), E96 ( ±1 %) and E192 (±0.5%, ±0.25% and ±0.1%) packages. Because they have better performance than carbon film resistors and are inexpensive, they are used in most applications. Their temperature coefficient (TC) is around ±100 ppm/K- some parts have positive TC while others have negative TC.

Carbon composition resistors were widely used in electronic devices fifty years ago, but because of their large variations and poor stability, they have been replaced by carbon or metal film resistors. However, they have good high frequency characteristics and are good at withstanding high energy pulses, and are still used today in welding equipment and high voltage power supplies.

Metal oxide resistors were the first alternatives to carbon composition resistors, but are being replaced by metal film resistors for most applications. They are still used for high endurance applications as they can handle higher temperatures and have higher power ratings (>1W).

The EIA Decade Resistor Values table can be used to match tolerances with values. For example, standard E12 (± 10%) decade values are 100Ω, 120Ω, 150Ω, 180Ω, 220Ω, 270Ω, 330Ω, 390Ω, 470Ω, 560Ω, 680Ω, and 820Ω.

Color codes are used to represent the values in through-hole resistors. You can use this Color Code Calculator to decode the color bands.

color

Part Selection:
Carbon Film Resistors: Yageo’s CFR-25JB series for 1Ω to 10MΩ rated at 0.25W
Metal Film Resistors: Yageo’s MFR-25FBF series for 10Ω to 1MΩ rated at 0.25W [CPL]

III. Wirewound Resistors resistor

Wirewound resistors have high-resistance wire wrapped around an insulating core. They can provide very high power ratings (up to 1000W) and can operate at very high temperatures (up to 300 degrees C). They also have good long term stability —  a change of 15-50 ppm/year compared to metal film resistors, which have a change of 200-600 ppm/year. They are the best choice for noise performance followed by metal film resistors.

Disadvantages: They are only available in low ohmic range (0.1Ω to 100kΩ). Because the wire is wound to create resistance, they have their own inductance, so they have the worst high frequency properties among all resistor types. They are also more expensive than other common types of resistors.

Applications: They are commonly used in circuit breakers and as fuses because of their high power capabilities.

Part Selection:
Ohmite’s HS-25 series for 0.1Ω to 30kΩ rated at 25W
Vishay’s RH025 series for 0.05Ω to 95.2kΩ rated at 25W

IV. Current Sense Resistors resistors r7

Current sense resistors, also referred to as ‘shunt’ resistors, are used to monitor currents in a circuit by translating them into voltage drops that can be easily measured. They are low-resistance resistors with higher power ratings to handle large currents. One of their applications is current limiting with stepper motor driver chips.

Most current sense resistors have either two or four terminals. In the four terminal version, which is also called a Kelvin configuration, current is applied at two opposite terminals and voltage is sensed across the other two terminals. This configuration reduces the effect of temperature dependence on resistance and greatly improves stability of the sense circuit. It is used for applications that require high accuracy and temperature stability.

Two Terminal:
SMD:

1206 Ohmite’s MCS1632 series for 0.005Ω to 0.05Ω rated at 1W [CPL]
1206 Vishay’s WSLP1206 series for 0.005Ω to 0.05Ω rated at 1W [CPL]
Through-Hole:
Ohmite’s 12F series for 0.005Ω to 0.05Ω rated at 2W [CPL]
Vishay’s LVR03R series for 0.01Ω to 0.2Ω rated at 3W

Four Terminal (Kelvin Configuration):
SMD: 2512 Ohmite’s FC4L series for 0.001Ω to 0.05Ω rated at 2W
Through-Hole: Ohmite’s 13FP series for 0.005Ω to 0.1Ω rated at 3W

V. Thermistors resistor

Thermistors are resistors whose resistance changes significantly with a change in temperature.

Use NTC thermistors when you need a change in resistance over a wide range of temperatures. Their resistance decreases with temperature, and they are good choices for temperature sensors between -55C and 200C.

Use PTC thermistors when you require a sudden change in resistance at a certain temperature. They are popular for over-current protection applications. The hold current refers to the current when the PTC thermistor is definitely ‘short,’ and the trip current refers to the current when an PTC thermistor is definitely ‘open.’

PTC Resistors:
1812
Bourns’ MF-MSMF series for hold currents from 300mA to 2.6A.
1812 Littelfuse’s 1812L series for hold currents from 100mA to 3.5A
NTC Resistors:
0603 Murata’s NCP18WF series for 100Ω to 470kΩ
0603 Panasonic’s ERT-J1 series for 22Ω to 150kΩ

VI. Potentiometers potentiometers r10

Potentiometers provide variable resistance that can be be used in variety of applications such as amplifier gain control, circuit tuning and so on. Trimmer potentiometers (or trimpots) are small potentiometers that can be mounted on a PCB and adjusted using a screwdriver. Trimpots can either be SMD or through-hole and can have either have top or side adjusting orientation. They can also be either single-turn or multi-turn. Single-turn potentiometers are used in applications like amplifiers, which only require a single control. Multi-turn potentiometers are used for more precise control, and they can have up to 25 turns.

SMD:
Bourns’ TC33X-2 series for 100Ω to 1MΩ  [CPL]
Panasonic’s EVM-3YS series for 100Ω to 1MΩ
Single-Turn Potentiometers:
Bourns’ 3362P series for 10Ω to 1MΩ [CPL]
BI Technologies’ 25PR series for 100Ω to 100kΩ
Multi-Turn Potentiometers:
Bourns’ 3296W series for 10Ω to 5MΩ [CPL]
Vishay’s T93YA series for 10Ω to 1MΩ

This guide covers some of the most popular types of resistors. In addition to these, there are MELF resistors, metal foil resistors, ceramic resistors, varistors, photoresistors and resistor arrays, which all have unique advantages in either precision, performance, or compactness. However, in most electronic projects you are likely to see one of the six types that we have discussed in this guide. If you have any comments or suggestions on the part selection, drop us a note in our Slack chat room or in comments below. A guide on how to select inductors is coming next. Stay tuned!