Flyback 20kV from 24V

Note: this information is a little outdated.

Left picture: Arc to grounded tip. Right picture: capacitive current dishcharge. Screwdriver is not earthed!

This device is very similar to the 8kV 20kHz transformer. It differs in three points:

These differences result in a slightly changed schematic. The main switching transistor is now a 2N3055 capable of 60V and 15A peak. It must be mounted on a heat sink. It is also more endangered by over-voltage, so the 0.39uF cap was added. It doesn't much affect performance, but reduces spikes a lot. The flyback core and Earth lead should be connected to Ground to prevent unwanted feedback from the secondary. The NE555 circuit can be connected to any voltage, provided the 4.7Ohms resistor is adjusted such that the circuit draws about 0.5A. This is the maximum the driver transistors will take, but is necessary for the 2N3055 to work correctly. Adjust the frequency to suit your flyback and ears :-)

input/output power of my prototype was about as follows:

With no load, the transistor barely gets warm, when short-circuited it gets moderately hot (mounted on a big heatsink!).

This device is suitable for driving Jacobs ladders, Plasma globes etc, and as an input source for a cascade, provided the caps and diodes are capable of the high voltage.

Michael Huff has a MOSFET Version of this circuit as well as a feedback-based circuit (no NE555, much simpler) on his page, and reports good performance.

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Jochen Kronjaeger