The Tech Blog

Today let’s continue diving into resistors by exploring the different types based on their construction materials. The material used is important to understand its use cases where you might use one over the other.

Carbon/Ceramic Composition Resistor: These are among the oldest resistor types, made by combining carbon powder and a binding material as a cylindrical core. On top, you have a non-insulating cover for protection. Since the entire body core can conduct electricity, they withstand high-energy pulses. So suitable for surge protection and RF circuits. Since it’s a mixture core, tolerance is not great and can’t be tuned that easily.

Wirewound Resistor: As the name suggests, they are made by tightly winding a resistive metal wire, typically nichrome, around a non-conductive ceramic core. The core provides excellent thermal stability, allowing these resistors to handle high power levels and dissipate heat efficiently. The resistance value depends on the resistivity of the wire and thickness so you can get good precision with it. The drawback is their inherent inductance(basically it’s a coiled wire). So for high freq signals, this resistor is not used widely.. There are variations of this resistor with reduced inductance via certain counter-winding techniques to cancel out the inductance. Overall, it is good for high-power DC applications.

Carbon Film Resistor: These are made by depositing a thin layer(film) of carbon on a ceramic substrate. To adjust the resistance value precisely, a helical or spiral groove is cut into the carbon film using lasers. This process effectively increases the length of the resistive path and allows for fine-tuning of the resistance. They provide better stability, precision and lower noise compared to carbon composition resistors. These are some of the common types seen in the through-hole resistor segment.

There are a few more in the list which we need to go over. Because of the word limit, I will explain them in the next post.

Last week, we dove into the fundamentals of resistance, exploring what it means and how it works. Continuing on that, folks starting out on electronics need to know how to read through resistors by appearance.

For through-hole resistors, a color code band system was introduced a century ago by the Radio Manufacturers Association (RMA) in the U.S. It became widely standardized as part of military requirements during World War 2. The first two (or three, in precision resistors) bands denote significant digits, the next one is a multiplier, and the final band represents tolerance. For example, a resistor with bands of brown, black, and red corresponds to 1, 0, and a multiplier of 100, making it a 1,000-ohm resistor (or 1 kΩ)

To make this easier to memorize, we use the classic mnemonic like: BB ROY of Great Britain had a Very Good Wife, which stands for Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Gray, White, representing the digits 0 through 9. The tolerance band is typically gold (±5%), silver (±10%), or none (±20%). Precision resistors can include additional bands for tighter tolerances.

SMD resistors use alphanumeric codes instead of color bands due to their compact size. There are different types here. In the Three-Digit Code type, the first two digits represent the significant figures, and the third digit is the multiplier. E.g, a resistor marked 472 means 47 × 10² = 4,700Ω. For a four-digit code, you get more range in resistors with the first three digits representing the significant figures, and the fourth digit being the multiplier. Eg. 1634 means 163 × 10⁴ Ω. Another type is EIA Codes(E6, E12, E24, E48, E96, E192) Which indicate value by 2 digits and letter as tolerance(Check images). The most common one is the E96 Code which defines 96 distinct resistance values within each decade(10-100 Ω, 100- 1 kΩ etc). 96 values in a decade are derived via a formula such that any resistor in the series is within ±1% of its nominal value.

Understanding these details isn’t just academic, it can be a lifesaver in the field, especially during troubleshooting. Take the time to learn them!