ESR is just what it says, resistance in series with your capacitor.Low ESR is important if there's a lot of ripple current in your capacitor. The RMS ripple current will cause heating (I^2R) losses in the capacitor, and additional ripple voltage.It will also affect the frequency response of your capacitor. The ESR zero formed by the RC circuit can actually help stability in a power supply control loop, at the expense of higher output ripple.So if your application has high ripple current and you don't need the ESR zero for stability then a low ESR cap will likely be the way to go.If you are looking for energy storage without large di/dt then a high capacity electrolytic is more appropriate. You should use a low ESR capacitor when the expected I^2 R heat loss (ripple current, squared, times the ESR), is too much heat for the component.Power-supply capacitors smoothripple on DC power supplied from AC sources. When the AC source islow frequency (50 Hz, 60 Hz, 120 Hz.) the capacitors are physicallylarge, and could tolerate high ESR (like, 1 ohm for a 1A supply with a 1000 uF filter capacitor). That's becausea one-amp ripple current only created one watt of heat, and a large (over a square inch of surface area) 1000uFcapacitor can shed that heat.When switchmode supplies went up to 50 kHz, and a suitable ideal-capacitor valuewas (again for 1A output) about 2.2 uF, 1 ohm ESR means that same 1W would be dumped intoa capacitor the size of a pea.
ESR-1976 Most Widely Accepted and Trusted Page 2 of 5 connections subject to tension, the least of the allowable pullout, pullover, and fastener tension strength found in Tables 2, 3 and 5, respectively, must be used for design. Typical Values of ESR It is not possible to provide a definitive rule for values of ESR that are acceptable for all situations. The expected value of ESR largely depends on the capacitance value and the voltage rating of the capacitor but also depends on temperature ratings.
It'd fail, becauseit's too small to dissipate one watt of heat.That isn't the full story (there might be local heating 'hot spots' even if theaverage dissipation seems supportable), so there are separate ESR and ripple current specifications.Capacitor ESR, outside of DC power supply filtering, is also of concern because itis an unwanted stray impedance. It may be discussed as 'dissipation factor', or 'loss tangent', or Q, and have significant frequency dependence.