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Re: [TCML] Feedback drive with a CT for a linear (non-DR) SSTC
Hi,
I might be all lost on this thread, but I trust you are aware of the
DF-DRSSTC that uses primary current through CTs to directly drive IGBTs
to run the coil:
http://hot-streamer.com/temp2/DF-DRSSTC-11.gif
http://hot-streamer.com/temp2/DF-DRSSTC-Wiring-Operation.pdf
http://hot-streamer.com/temp2/DF-DRSSTC-Notes.pdf
http://hot-streamer.com/temp2/DF-DRSSTC-MasterPartsList.pdf
Note that older references to the Hot-Streamer "temp" directory are now
the "temp2" directory due to Bill Gates being allowed to write software
:P The windows server no longer allows....... long story....
http://hot-streamer.com/temp2
Terry
Antonio Carlos M. de Queiroz wrote:
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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