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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
What sometimes happens in situations like these is that the core saturates a little, causing the primary to draw an unbalanced current with a DC component too, such that it cancels the DC amp-turns of the secondary and the saturation doesn't get any worse. Whoever said transformers don't pass DC?
This works in theory, and in practice on ordinary iron cored transformers running off 60Hz. But in high-frequency work, the primary DC component is drawn in short, high amplitude spikes, which usually end up blowing your drive transistors.
Of course, a flyback with a gapped core may be able to stand the DC amp-turns just fine without saturating much at all. Also, many drivers refuse to supply a DC component of primary current at all.
Registered Member #552
Joined: Mon Feb 26 2007, 08:42AM
Location: Galicia, Spain
Posts: 5
I'll try to make plasma in a bulb when i receive new transistro, they're coming ;). If the flyback's diode is still alive, the dc HV will not make too much plasma, just a little from the DC as it is unfiltered. If the diode is shorted, (i think that it will be) it will make lots of plasma, as it will be AC. But 50 KV without triplier seems to be... impossible. Think that the normal HV from a flyback uses to be over 30 KV with triplier, meaning that there's 10 KV in the secondary coil; 50KV on the secondary coil just can make me remember lots of smoke, transforming flybacks into smoke grenades . Al least that is what happended to me trying to put more than 30v in other flybacks.. secondary shorts and smoke everywhere.Also 2n3055s used to die in a few
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
David wrote ...
I'll try to make plasma in a bulb when i receive new transistro, they're coming ;). If the flyback's diode is still alive, the dc HV will not make too much plasma, just a little from the DC as it is unfiltered.
you know the hv rectifier(s) have died when there is strong corona between the flyback and its core, and the flyback usually doesn't stand this for long and arcs over (from secondary to core). If there is no corona at all, then your flyback hv rectifier is fine (and will not make a plasma globe even if it's unfiltered).
Registered Member #552
Joined: Mon Feb 26 2007, 08:42AM
Location: Galicia, Spain
Posts: 5
With DC flybacks I always could see a little plasma, like small corona, because plasma needs AC, so if DC is unfiltered it has a partial AC component. Diode died when arced to the core? I dont think so, it was on just a few, maybe 1 or 2 seconds before i disconnected it. I have never screwed a diode making arcs in dc flyback, just when imake long time arcs and the current is high it always fryes at the end. This flyback gets hot everywhere when i make long time arcs, lets say 1 or 2 minutes. Every thing inside of it may be frying, secondary coil, diode.. I dont use the internal capacitors, as I think that something gonna explode if i do so
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
David wrote ...
Finally, I recevived new IGBTs. The HV diode must be shorted, as it makes lots of plasma. So. I'm getting 50KV without multiplier
These flybacks are not meant to be run with a multiplier (but it is possible to do if you have shorted all the diodes ). My dc flyback can do 70kv and the diodes are still fine, and yes it makes lots of plasma and corona, but only when the gnd wire is brought close (~10cm) to the output.
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
David wrote ...
With DC flybacks I always could see a little plasma, like small corona, because plasma needs AC, so if DC is unfiltered it has a partial AC component. Diode died when arced to the core? I dont think so, it was on just a few, maybe 1 or 2 seconds before i disconnected it. I have never screwed a diode making arcs in dc flyback, just when imake long time arcs and the current is high it always fryes at the end. This flyback gets hot everywhere when i make long time arcs, lets say 1 or 2 minutes. Every thing inside of it may be frying, secondary coil, diode.. I dont use the internal capacitors, as I think that something gonna explode if i do so
Unfiltered DC won't have much of a 'partial AC component' in a plasma globe -- it's only by corona discharge and leakage that you can pass current -- imagine the interface between the filament/glass on your lightbulb as if it were a capacitor. It'll charge on the first half-wave... and then it'll stay charged. If the flyback had a center-tap, then you could extract an 'ac component'
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ZVS Flyback Driver Nice sparks!
. Al least that is what happended to me trying to put more than 30v in other flybacks.. secondary shorts and smoke everywhere.Also 2n3055s used to die in a few
). My dc flyback can do 70kv and the diodes are still fine, and yes it makes lots of plasma and corona, but only when the gnd wire is brought close (~10cm) to the output.
