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Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Won't the maximum output of any TV or monitor LOPT ultimately be governed by the properties of the core, and the current handling capacity of the secondary winding, rather than the exciting energy in the primary?
Most folk in 4HV seem to favour adding their own primary windings to the core, but I wonder how this can be more efficient than the metal tape low Z primary concentric with the secondary in the LOPT as is.
Registered Member #1389
Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
Well, for the ZVS driver to operate properly, it needs a center tapped primary with either leakage inductance or external inductance. The primary wound on the exposed limb conveniently gives both the center tap and the leakage inductance to limit the resonant frequency and primary current to something reasonable. I suppose with a primary on the same limb as the secondary, you can control all the aspects of the ZVS driver - primary current, resonant frequency, capacitance, and primary inductance. And yes, the power throughput is limited by core and copper losses, rather than core saturation or exciting energy.
As for the arc's power, I really don't know. If I had to throw out a number, I'd conservatively say 500W. I'd like to think it was upwards of 1kW.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
I was analyzing the zvs driver, and observed what is the function of the series inductor. Its function is to remove the coupling between the two halves of the primary coil. The oscillator works better with two uncoupled coils in the driver, but as they are wound in the same core this is impossible. But the extra inductor cancels the coupling. The best value of its inductance is around the same inductance of one of the primary coils. With too low inductance, the oscillator enters a curious asymmetrical oscillation mode, probably destructive. With too much inductance it works, but takes longer to stabilize after changes in the load and at startup.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
The series inductor is to "compensate" for the voltage difference between the DC supply voltage and sine wave on the primary, and it also serves as a (more-or-less) constant current source over each period. With too low value, the current increases towards each half-cycle end, the primary sinewave distorts and transistors heat up. On the other hand, too high inductance is OK, but the inductor comes out physically larger.
The coupling of the two primary coil halves is a function of their geometry and position on the core, and is constant for a given coil configuration.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Yes, the ZVS is just a current-source inverter, and these are well known and described in the literature. You can also make half-bridge (with a 2-winding DC link inductor) and full-bridge versions.
Current-source inverters are "duals" of the ordinary inverter circuits we're familiar with. The idea of duality is that currents take the place of voltages, inductances take the place of capacitances, parallel and series change places, short and open circuits change places.
A current-source inverter is short-circuit proof, but will be destroyed by an open circuit.
A current-source inverter can drive a parallel resonant load, whereas a voltage source inverter needs a series resonant load.
According to duality, the function of the DC link choke is the dual of the function of the DC link smoothing capacitor in an ordinary inverter. It keeps the DC link current constant. In analysis, it's often assumed infinitely large, without thinking too much about how the current got to the assumed value in the first place. And so on.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
I've always had difficulty with claims of 1KW o/p from a 110W LOPT. How is the kilowatt OP to be deconstructed as volts and amperes?
Why are there never any figures? It doesn't take the brains of an Archbishop to measure EHT, so why is nothing ever laid out before us - year after year - in an empirical way from the 'flyback' fraternity? How could such small structures allow 1kW without material damage, and so on?
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
Flyback experimentation is sort of entry level stuff, so most experimenters only have the most basic tools. As Steve says it's not even easy for someone in a well equipped lab to measure this stuff. Just now I measured the power draw from my little half-bridge driven flyback transformer, using a kill-a-watt meter. Open circuit the power draw is 50W, losses in the IRFP450s mostly I'd assume, since the magnetizing current in this transformer is pretty high. The power draw at the end of an arc is 470W. So Firefox'es 1kW claim isn't off the wall. With so much effort just put into getting this stuff not to explode, getting consistent and repeatable results is just a dream for most of us.
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