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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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