This was my second attempt to go solid state with my Tesla coils and was built during the fall and winter of my freshman year of high school (2009 – 2010). It was later improved and upgraded during the winter and spring of my sophomore year (2010 – 2011). At one point, this included the addition of a resonant capacitor, technically making it a Dual Resonant Solid State Tesla Coil (DRSSTC), however, this was later removed due to repeated MOSFET failure stemming from excessive current in the primary circuit and racing sparks caused by the increased performance.
Antenna feedback was used in this coil to automatically bring it to resonance without the hassle of tuning a fixed frequency oscillator. Because this was my first serious venture into solid state coiling, I tried to keep the design as simple as I could and used a scheme that was essentially nothing more than Steve Ward’s SSTC 5 with a few modifications in the power section and an added external interrupter port.
During each operating cycle, the antenna picks up the electrostatic field generated by the secondary coil and sends it directly to the 74HC14 inverter chip. A pair of 1N4148 diodes clamp the voltage down to 5V to keep the high voltage on the antenna from frying the low voltage TTL logic chip. Next, two series-connected logic inverters in the chip function as a buffer and send the signal to the UCC3732x gate drivers. Although the circuit may still work without the inverter stage, it is advisable not to omit it as it greatly increases the stability of the system. One of the gate drivers is inverting while the other on is not, creating a 24V peak to peak signal across the gate drive transformer as one “pushes” while the other “pulls”. One the other side of the transformer, a half-bridge of MOSFETs switches current back and forth across the primary coil at a frequency that resonates with the secondary coil and this creates massive voltage spikes that manifest themselves like so:
(This picture is from late December of 2009)