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Re: [TCML] Feedback drive with a CT for a linear (non-DR) SSTC
TheBypasser wrote:
... but I've got the one last problem - the feedback itself. I thought
of using a CT rigged up to the secondary ground, but the calculations
proved that it's not as clear as it seems. Normally the secondary
current is less then 3 Amps, so the CT ratio should be pretty high in
order to get it properly loaded the whole secondary duty cycle by
means of the driver's input zeners or diode fork. If the correct load
is not present, the voltage output fase of the CT will get displaced
so will get fased more like the input voltage, not current - eg. up to
90 deg shift. Should I wind a 200 turn CT (I plan to load it with 15v
zeners and then send the signal into the system itself through a 1k
resistor, a 100n cap and a diode fork to normalize it to 5v for the
logic to accept), or it's not necessary and even 100 turns will be ok
(the secondary is a 150kHz 37x18cm one)? Or I should use no CT at all
and just attach an antenna feedback? I'm not really happy about the
antenna idea as it limits the coil positioning and adds some risk of
arcover..
Why don't you use primary current feedback? Just pass a wire
transporting the current trough a suitable toroidal ferrite core, wrap
some turns with another wire in the core to have an inductance L, and
load the coil with a series RC circuit. The voltage waveform over the
capacitor is a practically exact copy of the current. The circuit is a
bandpass filter, with lower cutoff frequency at f1=1/(2*pi*R*C) and
upper cutoff frequency at f2=R/(2*pi*L). For a current I, the output
voltage is V=I*M/(R*C), where M is the mutual inductance between the
wire and the coil, to be found experimentally. It is practically
independent of the exact position of the wire inside the toroid.
Antonio Carlos M. de Queiroz
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