How to Read Color-Coded Diodes

By Andrea Walk

Diodes are electronic components that are similar in nature to resistors. Resistors block the flow of current across the entire circuit, though, whereas a diode allows current to pass one way, but blocks current in the opposite direction. Diodes are sometimes used in converting alternating current to direct current. There are different types of diodes. Some have their values marked clearly on them. However, other diodes use the color-coding system that resistors use. Reading and deciphering the diode value is easy if you have a color chart reference sheet.

Turn the diode in your hand so that the bands are on the left hand side and the non-banded side is on the right. The left, banded side, is known as the cathode end and the nonbanded end is the anode.

Consult a diode color code chart and familiarize yourself with the coding system. The values of the chart are 0 for black, 1 for brown, 2 for red, 3 for orange, 4 for yellow, 5 for green, 6 for blue, 7 for violet, 8 for gray and 9 for white.

Jot the number values down, moving from left to right, for the first two bands.

Determine the tolerance rating for the diode by examining the third band. The tolerance rating is the number of zeroes that are in the total value of the diode. For example, a diode marked with the colors yellow, orange, red would be equal to 4,300 Ohms.

Calculate the fourth band if there is one on the diode. Some diodes have a fourth band that is either gold or silver. These bands are accuracy tolerance bands and are used on precision diodes. Gold has a value of plus or minus 5 percent. Silver has a value of plus or minus 10 percent. On diodes with accuracy tolerance bands, the respective percent values are subtracted or added to the end value of the first two to three color bands.