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High Voltage CW Phase Shifter
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Univie:
My goal is to generate two identical high voltage continuous-wave signals of around 3-5MHz, one being shifted by around 63 degrees relative to the other. The outputs are capacitive.
I’m currently achieving this using a simple ’slayer exciter’ circuit to generate the first HV signal, and a capacitively coupled air-core coil to generate the other. The coil is tuned slightly inductive (>90deg) to generate the needed phase shift.
The problem with my very simple setup is that the self-tuning of the slayer exciter is disturbed by the capacitive coupling of the passive coil, unless the coupling is kept very low. I’d be happy to hear suggestions of an alternative method that would not be sensitive to this coupling effect.
bob91343:
You are taking the output from the most sensitive point, the base of the transistor. I suggest adding an emitter resistor and taking the output from the emitter.
I ran into a similar question years ago when a student was trying to send a signal but the stability was poor. Taking it from the emitter helped a great deal but still too sensitive. I suggested a crystal oscillator, which solved the problem. He won a cash award with that and I asked for my cut. He started to panic so I told him I was just kidding.
Univie:
Thanks for the reply, I may have to consider a crystal oscillator, since I also need bipolar output, while the slayer exciter has the secondary grounded at one end. (I still get bipolar output now, but only because my 'ground' consists of a small heatsink on the bjt). Do you think that tuned-circuit oscillators like Colpitts or grounded-base would also be disturbed by the coupling of the secondary to another coil capacitively?
Or could I have a single oscillator driving two primaries (see diagram), which induce currents in two different secondaries, such that the phase shift between the secondaries is the required phase shift. For example, the first secondary could be slightly capacitive (relative to primary) by half the needed phase-shift (31.5 deg), and the other secondary slightly inductive, providing the other half of the phase shift. Would a crystal oscillator topology allow for something like this?
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