Andreas wrote:
For a 48kOhm secondary reactance, that means secondary
voltage output due to resonant rise should be about 8.3kV
(48kOhm * .170mA) ...
... 18V * 2A = 36W in to the primary.
... 8.3kV * 170mA means 1400W sloshing about in
the secondary circuit...
Seems reasonable to have 1400W of reactive power in the secondary,
this is the stored energy exchanging back and forth between L and C
on each RF cycle.
The stored energy is
Xl * I_rms^2 / (2 * pi * F)
= 48k * 170mA^2 / (2 * pi * 500kHz)
= .00044 Joules
The storage efficiency is measured by the Q factor:
Q = 2 * pi * F * stored_energy / power_input
= reactive_power / power_input
where power_input is equal to the power dissipated once the
oscillation has 'rung up' to a steady state.
Some of your 36W DC input is replacing the energy dissipated
each second. If the oscillator and primary were 100% efficient
so that all the 36W goes into the secondary, then the Q would
be around 1400 / 36 ~= 40
If the efficiency was 50%, then Q would be 80, and so on.
Typically secondary Q factors are in the range of 50 to 200 or so.
A good oscillator/primary efficiency might be 70%, and 90% or more
would be excellent.
Measure Q independently by measuring the 3dB bandwidth,
then back-calculate efficiency.
--
Paul Nicholson
--
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