On Apr 16, 10:31*am, Cecil Moore wrote:
Roger Sparks wrote:
This WIKI article mentions the ability of an ideal voltage source to absorb power.
It says: "A primary voltage source can supply (or absorb)
energy ..."
That's easy to comprehend for a battery source. Not so
easy for an ideal RF source with a zero series impedance.
If we define an RF source as a coherent RF battery, anything
is possible (at least in our minds). Which of the following
makes more sense?
Neither. See 3.
1. Destructive interference energy is stored somewhere
in the system and delivered back to the system 90 degrees
later in the cycle just as it is by a physical inductor
or capacitor.
2. An RF battery inside the ideal source stores the extra energy
in coherent RF form and delivers it back to the system as needed.
3. An ideal source provides or absorbs energy to satisfy its
basic function which is to hold the voltage across its terminals
at the desired value. When it is providing energy we do not know
where this energy comes from and when it is absorbing energy we
do not know where this energy goes.
http://en.wikipedia.org/wiki/Voltage_source
It also says: "The internal resistance of an ideal voltage
source is zero;" So exactly how does something with an
internal resistance of zero absorb any power?
Unknown. Just as we do not know where the energy that an ideal
voltage source sometimes provides comes from.
But you are invited to speculate on the many ways that it might
be done. Just as you might speculate on where the ideal voltage
source gets its energy when it is providing energy to the
circuit.
Just as there are real devices which approximate ideal voltage
sources delivering energy to a circuit (commonly called power
supplies), there are devices which approximate ideal voltage
sources that remove energy from a circuit. Check the Agilent
catalog for "DC Loads". Perhaps the schematic will provide
what you seek. Of course power supplies and DC loads are
typically one quadrant devices, but with a little ingenuity
you can combine them to form a two quadrant device which
would be an even better approximation to an ideal voltage
source.
...Keith