On Fri, Jan 23, 2004 at 02:34:22AM -0000, Konstantinos Bibis wrote:
> I understand that. What i dont get is why and how is the unit
> consuming energy by doing nothing. After the tube is charged, does it
> need more power to conserve this charge ?
> It's not like let's say a capacitor where when it's charged it's
> charged?
Yes, it's storing charge in a capacitor, and yes, you would think that it
wouldn't require much power to maintain it, since the self-discharge of the
capacitor should occur very, very slowly. But no matter how slowly, it will
require a periodic recharge to keep it "topped off". Also, the type of
charging circuit used in modern flashes depends on monitoring the voltage on
the main capacitor so that it knows when the capacitor is fully charged - but
the monitoring circuit itself drains charge from the capacitor, increasing the
standby discharge rate.
The Canon approach to keeping the capacitor charged seems to be a bit
aggressive; it fires off several times a second. Once the capacitor is mostly
charged, the charging circuit probably isn't very efficient, so most of the
power it consumes is wasted.
In the case of the 540EZ, after the capacitor is fully charged, the baseline
current drain is about 50mA. The charging circuit kicks in at 100ms intervals
for about 7ms (7% duty cycle), drawing about 800mA, which accounts for another
50+mA on average.
So, about half of the standy current consumption is used to maintain the
capacitor charge and about half by the rest of the circuitry - the flash's CPU,
monitoring circuitry, indicators, and such.
Note, all of above is based on watching the battery current with an
oscilloscope and having designed & built many many xenon strobe circuits, so it
isn't neccessarily correct :)
John
--
John DuBois [EMAIL PROTECTED] KC6QKZ/AE http://www.armory.com/~spcecdt/
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