Experiments with flybacks


Posted on Feb 6, 2014

The first attempt used a small flyback from an old computer and a simple driver based on a 555 IC with AC coupling to the driver transistor, with this schematic diagram. It was assembled in a perforated board and put in a box. The circuit has two possible power supply voltages for the flyback, a discrete 12 V voltage regulator, and a 555 astable oscillator where the frequency


Experiments with flybacks
Click here to download the full size of the above Circuit.

and the duty cycle can be varied, although not independently. It is similar to other drivers that can be found in the Internet. I tested it by producing sparks between balls. The spark length between balls is a precise measurement of the available voltage. In these experiments, I put 500 kOhms of resistance (5 1 W 100 kOhms resistors) in series with the output, and a 50 pF Leyden jar across the spark gap. Without the jar, the sparks are weaker an blue or violet. It produces about 20 kV, at a few mA. This circuit had problems with excessive power dissipation in some resistors (R1 and R3) and insufficient base drive for the power transistor when the duty cycle was high with 50 V supply, due to the AC coupling. The small flyback had also a tendency to spark to its core, to the box, and to the heat sink of the power transistor. It also had not enough power to power a "lifter". The insulation problem was solved by filling the tube where the output cable enters the transformer with silicone glue. The power supply can now power a Jacob`s ladder without problems. I could also make the circuit generate enough voltage for a "lifter" (see below) by replacing the snubber network by a simple 4. 3 nF 1600 V capacitor: The second version uses a bigger flyback transformer and a better system to drive the power transistor from the 555, producing a base current in the form of a ramp, following the collector current, that is also a ramp in...




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