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Registered Member #8120
Joined: Thu Nov 15 2012, 06:06PM
Location: Moscow, Russia
Posts: 94
Resistors to limit current, bad idea? Removed them, no effect. Checked everything, and turns out one of the tubes had bad connection on the heater. With that fixed, i'm getting about 1.5V unloaded output with tiny current, at 1KV input...
So i decided to go for broke, and pulled out the flyback.
At 20KV input voltage i am getting 350V out unloaded. The current, unfortunately, is tiny. 140V at 1M load, 25V at 100k load. Or, 0.01W out.
The highest efficiency is at about 140KHz, going down both at 80, 260, and 23 KHz. Added a couple more turns to the secondary, and am getting 36V at 100K load.
I suspect that you'll need to design the transformer properly for the task. Adding a gap reduces output significantly. So, more primary turns. Much more, if the input currents are to be in the low mA range. But i'm not willing to make a multi-turn HV coil just to test it out...
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Marko has built a nice half-bridge converter using TV sweep tubes, with wireless filament power for the high side. It seemed to work well with several kV input.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
A noisy, lossy and simple approach could be a DC RSGTC-like arrangement, except the secondary coil would have less turns than the primary coil. Or replace the air core transformer with a ferrite or iron core one.
Registered Member #5323
Joined: Fri Jun 15 2012, 02:14PM
Location:
Posts: 104
Revisiting the configuration of using a spark gap (or gas-filled spark arrestor) as the HV switch connected through a MOT to step down the HV to LV.
Question: Considering the difficulty in locating a semiconductor HV switch that can handle these extreme high voltages, would using a spark gap as the HV switch be the next reasonable choice? Or am I wasting most of the system's energy in the spark as heat, light, EMP, gamma ray, noise?
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
A spark gap can be used as switch in a buck converter in a situation where something charges a capacitor to high voltage and the converter is used to transfer all the energy in this capacitor to another at low voltage, discharging it completely. You need then just a diode and an inductor capable of sustaining the full voltage and a load capacitor big enough to receive the total energy. The gap would spark when the first capacitor reaches enough voltage, and conduct until the current ceases. A diode in series with the inductor may be added to avoid any energy return, and a resistor in parallel with the inductor may be added to guarantee a minimum current for the initial spark. The losses in this situation may be moderate. If the source is a voltage source the switch would have to be turned off periodically, and there is no way to turn off a spark gap.
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Rare HV to LV converter
