> What do you mean by lower bandwidth for batteries? I understand your > other two points, but I am not grasping this one.
D.C. power supplies are often considered as simply DC, i.e. thay have no AC content, but of course the reality is this is never the case. For a PSU that experiences a dynamically changing load, as most do, it's response to this is important. In an active regulator, it is attempting to keep it's output constant, based upon the changes it measures through it's (internal or external) feedback connections. The load placed upon any power supply will have an inherent bandwidth, i.e. it will be making current demands upon that power supply, in relation to it's own internal activity. In the case of something like an audio amp, the demands placed upon the PSU will be related to the audio frequencies it's dealing with, primarily, in the case of digital they will be related to clock speeds and edge transitions, which can generate very high frequency demands on a PSU. The reality is one can never deal with very high frequency demands actively, only through passive means, like decoupling etc. The bandwidth of a PSU therefore needs carefully defining, in order to ensure it is capable of meeting the demands of the loads placed upon it, and keeping the supply within the design criteria. For feedback based regulators one needs to define these bandwidths very precisely to ensure that the system is stable and performs as expected. The regulator can affect the system being powered, but equally the system can affect the performance of the regulator, in a critical manner - it's for this reason it's much harder to do stuff actively. For batteries, the ability of the system to respond to transient (and by definition higher-frequency) demands, is related to the ability of the battery to maintain a constant DC potential, which is related to the internal impedance of the cells and the chemical reaction that goes on internally. A chemical reaction is, by it's inherent nature, slow in comparison to the demands of either an audio, or particularly, a digital system. It also tends to be ill-defined in terms of response to a transient demand, which from my perspective makes batteries a poor choice unless care is taken to limit the demands placed upon them, which ususally requires active circuitry after them, to acheive this. Andy. -- Andrew L. Weekes _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
