Equivalent series resistance

Equivalent series resistance (ESR) is a lumped resistance used to model a component’s internal resistive losses, especially in capacitors and batteries. It accounts for voltage drop and heat dissipation under current.

Ohm's law: The relation between voltage, current, and resistance expressed as V = IR. ESR produces an internal voltage drop proportional to current.
Electrolytic capacitor: A capacitor that uses an electrolyte as one electrode and a thin oxide layer as its dielectric. Its ESR can rise with age and strongly affect ripple heating.
Capacitance: A measure of how much electric charge a component stores per unit voltage. Capacitance and ESR together shape a real capacitor’s circuit behavior.
Ideal capacitor: A theoretical capacitor with capacitance but no resistance, inductance, leakage, or dielectric loss. Unlike this idealization, a real capacitor dissipates energy through ESR.
Joule heating: The conversion of electrical energy into heat when current flows through resistance. Current through ESR dissipates power as heat, approximately I²R.
Switch-mode power supply: A power converter that regulates voltage by rapidly switching semiconductor devices. Output-capacitor ESR influences ripple voltage and converter stability.
Equivalent series inductance: A lumped inductance representing a component’s internal and connection-related magnetic effects. ESL accompanies ESR in practical capacitor models, especially at high frequencies.
Parallel equivalent resistance: A resistance connected in parallel in a simplified model of a component’s losses. Parallel and series resistance models represent losses differently and are not interchangeable in every regime.
Impedance: The frequency-dependent opposition that a circuit presents to alternating current. ESR is the resistive part of a component’s broader impedance.
Low-ESR capacitor: A capacitor designed to have relatively small equivalent series resistance over a specified frequency range. These capacitors limit ripple losses in high-current power circuits.

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