Audio Modulated 555 Flyback Driver

The core of this driver consists of probably the most popular IC of all ages, NE555 timer, configured as an astable oscillator producing a square wave output, fed into the MOSFET, driving the primary of a flyback transformer.

The switching frequency can be calculated using formula: $$f = \frac{1.44}{(R_{1}+2R_{2})C}$$

This circuit uses C=2.2nF, R1=1kΩ, R2=10kΩ + (10kΩ potentiometer), which results in output frequency range: $$f = 16kHz - 31kHz$$

The output frequency can be furthermore modulated by varying the voltage on pin 5 (CV). By connecting an AC-coupled audio signal, the FM induces an audible response present in the arc (plasma speaker).