Click here to view Circuit
This is an efficient fly back driver for
modern cylindrical rectified television fly backs. Many
sites doesn't provide circuits driving these
transformers, they simply say that they are bad.
I don't agree. In fact I built this
circuit. I spent a lot of time for finding resonant
frequency (around 15Khz) and duty cycle. These
transformers best work at around 90% duty cycle. You may
notice corona breakdown at terminals and puffs sound (as
well as the ozone smell) when adjusting the off time
trimmer to near 500-300 ohms. Of course it will work for
other types of fly back as frequency and duty cycle have
a large range.
Frequency range can be increased using
multi position switch for other values of C3 capacitor
,for example 2 of for 80KHz-200000KHz, but didn't found
fly backs with so high resonant frequencies, in addition
with higher values of c3 , eg 200nF, 2uF the frequency
will drop making possible the use of ignition coils, and
rectified power transformers @50Hz to charge high
voltage electrolytic caps at 300-400V). Unfortunately my
ignition coil died because insulation breakdown (too
long drawn arcs)...
I was able to power a small (20cm) Spark
Gap tesla coil Using these dc rectified fly backs to
charge primary tank capacitor.
The 555 is wired as an astable and the
capacitor is charged only through the 4,7Kohm trimmer
(notice the diode) and discharged only through the 2.2
Kohm trimmer, making the duty cycle full adjustable. The
square wave is then feed in a totem pole made up of a
2N3904 and a 2N3906, which are cheap, and easy to find.
The totem pole ensures the gate being charged and
discharged very fast (approx 50nS i think). The IRF840
is a cheap (i found it for 4euros) reliable and powerful
power mosfet, it has current capability of 8 A
continuous and 32A pulse, 800V drain source voltage,
protecting internal zener diode. There is a snubbing
network to ensure that voltage spikes are kept low
(unless the insulation of the transformer start to leak)
protecting both transistors and 555 IC. 100 ohm is a
compromise between decay time and voltage spike.
-
The 100 ohm snubber must me a 5W
resistor, or it will burn at long operations
-
The led is only for safety purposes
-
Use a dead man switch (pushbutton) for
safety
-
The power supply must supply at least
2-3 A if you want decent arcs (20000 KV)
-
The flyback driven in this way can
supply a significant current, aldough the heart
fibrillation starts at 30mA
-
I recommend caution to avoid painful
arc-burns.
-
The arc is a hot plasma, never operate
the circuit in presence of flammable substances.
-
Charging high voltage capacitors is a
serious life threat, so if you arent unexperienced just
draw arcs and no more
-
This device when rectified generates
static voltage that can be a little annoying.... (or
fun, i sprayed with corona
-
a plastic pen from positive terminal and
then i was able to attract little pieces of paper)
I don't assume any responsibility of the
damages or discruptions dove by this device, to persons
or things. Any irresponsable action would be a serios
danger. This is high voltage threat it with respect.
|