Table of Contents
Parallel Resistors
Resistors in parallel share the same voltage across their terminals. The total current is the sum of currents through each resistor. Because more paths are available for current flow, the total resistance decreases. The parallel combination is always less than the smallest individual resistor.
Parallel resistor networks are fundamental building blocks in electronic circuits. They are used in voltage dividers, current sharing, impedance matching, and to create non-standard resistance values from standard components. Understanding parallel resistance is essential for circuit analysis using Kirchhoff's current law.
Formula
Quick Rules
- n identical resistors R in parallel: total = R/n
- Two equal resistors: total = R/2
- Result is always less than the smallest resistor
- Adding more resistors always decreases total resistance
Frequently Asked Questions
How do I find a target resistance using standard values?
Use the product-over-sum formula: if you need Rtarget, find two standard values where R1×R2/(R1+R2) = Rtarget. For example, 100Ω and 100Ω in parallel give 50Ω. Online parallel resistor calculators can suggest optimal combinations from standard E-series values.
Does the power rating change in parallel?
Each resistor must individually handle its own power dissipation. The total power handling of the combination is the sum of individual ratings only if all resistors are identical. For unequal values, the lowest-value resistor carries the most current and may exceed its rating first.