This SSTC is a quick coil I put together during one of my summer vacations
while studying for my masters degree, in 2013. It was mostly so I had a small coil
I could keep in dormatory to show friends. There were more than a few nights
where minds weren't the sharpest and chances were taken, but for the most part
the only damage happened to the coil itself. The design is based on my experiences
with the PLL SSTC 1 and
PLL SSTC 2, with some
minor simplifications and improvements. It was originally built without a topload,
but it liked to breakout from the secondary wire leading to the actual breakout
point, which causes burns and small fires on a few occasions. To rememdy this,
I put a topload on the coil, and retuned, but not until 2022!
The operation of the circuit is explained on the PLL SSTC 1 page, so I
won't repeat it here. The main changes and improvements are using a regulated
5V supply dedicated to the PLL. As it contains voltage sensitive VCO, this
is quite crucial for stable performance. Otherwise it uses a current transformer
for feeback, which makes it easier to build into a enclosure, and less likely to
pick up random noise. The GDT primary damping resistor should be sized so waveforms
are just good enough. This relieves stress on the UCC gate drivers. The other
function is to transfer some power loss into the resistor rather than the gate
drivers. For my setup I used a resistor of 5 Ohms, rated for 10W of power. To
reduce noise and induced mains current problems, Y-rated decoupling
capacitors are placed across the mains lines and ground. The idea here being that
in an apartment or similar without ground wires, the induced current in the mains
lines will have a defined return path to the secondary ground wire.
Set up used when finding the resonant frequency. A oscillioscope probe is placed in the air near the topload, and the ground clip fastened to the secondary bottom. The primary is driven by a frequency generator.
Tuning tips
These are also stated on the PLL SSTC 1 page, but I'll repeat them here.
A sharp breakout point is needed. It is not enough that it is sharp, but it must be far away from the electric field
generated by the topload as well. A large topload is ok, but the breakout point needs to be moved far away from it
in order for breakout to occur. A poor breakout point seems to make the system work unreliably. In some of my other coils
with toploads, it wouldn't work at all until making a longer breakout point. Performance wasn't acceptable until the
breakout point was placed far from the topload.
If using a current transformer for feedback rather than an antenna, the polarity is important. Change by switching
which direction the ground wire enters the current transformer.
Tuning the PLL is somewhat tricky. Unsure if breakout point issues were the main culprit or not. If building this,
consider using potentiometers for the timing resistors, in addition to the phase adjustment potentiometer.
Disclaimer:
I do not take responsibility for any injury, death, hurt ego, or other
forms of personal damage which may result from recreating these
experiments. Projects are merely presented as a source of inspiration,
and should only be conducted by responsible individuals, or under the
supervision of responsible individuals. It is your own life, so proceed
at your own risk! All projects are for noncommercial use only.
This work is licensed under a
Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
