Hello,
It's also dependent on frequency.. If the 'lytic cap in question is used in a good old fashioned line frequency copper/iron power transformer, the ESR requirement is not very high since ripple frequency for a full wave rectifier is 120 Hz in the US and 100 Hz in other parts of the world. Most any garden variety cap should be good for this.
Not true for high frequency switching power supply capacitors. As the Equivalent Series Resistance goes up, the losses per cycle goes up too which causes internal heating inside the capacitor and shortens it's life. This is why capacitors have a ripple current rating on top of the ESR spec.
Many of the current generation low ERS capacitors are designed for use in switching power supplies and one look should examine the ESR vs Frequency curve to decide if this part will work for it's intended application. Ripple current vs frequency is another consideration along with max temperature which is usually +85 or +125 degrees C. There is also a life rating in hours based on temperature and ripple current.
Be aware that while the new generation of smaller 'lytics pack a lot of capacitance and performance in a small package, they can be short lived. Hour ratings of 2,000 hours at it rated ripple current and temperature. Expected capacitor life is quite dependent on operating temperature and circuit conditions. They are a wear out part in just about every electronic device :(
Bernice
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--- On Thu, 10/2/08, Jerry Massengale <jmassen418@...> wrote:
The ESR is critical to ripple.
