Resistor Wattage Calculator
Calculate power dissipation, thermal derating, and safety factors for resistor selection
Power Calculation Parameters
Voltage across the resistor
Resistance value
Standard Power Ratings
Package Details
Safety Guidelines
Use 2-3× safety factor for reliability
Consider ambient temperature derating
Larger packages dissipate heat better
Monitor junction temperature
Use power resistors for high power
Understanding Resistor Power Dissipation
What is Power Dissipation?
Power dissipation in resistors is the conversion of electrical energy into heat energy. When current flows through a resistor, electrons collide with atoms in the resistive material, converting kinetic energy into thermal energy. This process is governed by fundamental electrical laws and thermal physics.
Key Power Formulas
- •P = V² / R (when voltage and resistance are known)
- •P = I² × R (when current and resistance are known)
- •P = V × I (when voltage and current are known)
- •All derived from Ohm's Law: V = I × R
Thermal Considerations
Temperature Rise: ΔT = P × θ_ja
Junction Temperature: T_j = T_a + ΔT
Derating: P_derated = P_max × derating_factor
Safety Factor: P_safe = P_max / safety_factor
Design Considerations
- •Choose power rating 2-3× actual dissipation
- •Consider ambient temperature variations
- •Account for thermal resistance to ambient
- •Use proper PCB layout for heat dissipation
- •Monitor junction temperature in operation