Steve said:
So say I've only a pretty crappy low voltage available, like 5V say,
and I want to momentarily whack a capactior up to say 15V, could I do
it by pumping a short but powerful 'packet' (or *packets* ) of charge
from the 5V source into it? Would the capactior store the excess
charge in the form of excess voltage accross its plates if you get
what i mean?
tnx
Another way to do this is with an inductive spike. Inductors like to
keep current flowing through them. Thus, if you get current flowing, and
then cut it off suddenly, the voltage at the point you cut it off will
spike due to the sudden extra electrons (or lack thereof).
This is how DC-DC boost converters work. They have an oscillator that
turns on and off current through an inductor, and tap the point where
the inductor and transistor meet (the point with the voltage spikes)
with a diode pointing away from the junction. They then charge up a
capacitor with the 'packets' of charge that the inductor keeps sending
in, regardless of the voltage. A feedback mechanism turns off the
oscillator when the voltage reaches the point the circuit is designed to
get to.
The amount of power that can be taken from a circuit like this is
defined by the frequency and duty cycle of the oscillator, the
inductance of the inductor, and the voltage across it when charging.
You can buy these dc-dc converters off the shelf for various voltages,
or build them pretty easily. White light LEDs require about 4V to light,
but they can be lit from a single 1.5V AA battery using a simple circuit
like this.
--
Regards,
Robert Monsen
"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.