HALF-BRIDGE SOLID STATE TESLA COIL:

FULL INSTRUCTIONS
You will need the following parts:
Main SSTC circuit
 Two high-power IGBTs (FGA60N65SMD)
 One UCC27425 gate driver IC (UCC27425P or UCC27425PE4)
 One 74HC14 hex inverter Schmitt trigger (SN74HC14AN, TC74HC14APF, or
SN74HC14N)
 One 555 timer (NE555P)
 One 7812 12V linear voltage regulator (L7812CV)
 One 7805 5V linear voltage regulator (L7805CV)
 Four 1N4148 diodes
 Two 1N4007 diodes
 One 25V/220uF electrolytic capacitor (must have 3.5mm lead spacing to
fit PCB and be 25V or greater)
 Two 25V/470uF electrolytic capacitors (must have 5mm lead spacing to fit
PCB and be 25V or greater)
 One 5K resistor
 Two 6.8 ohm resistors
 One 50K resistor
 One 2.2K resistor
 One 1K resistor
 One 2M potentiometer
 One 50K potentiometer
 One ON/OFF switch
 One 1uF ceramic capacitor (50V recommended)
 Two 0.1uF film capacitor (10mm lead spacing, rated over 50V)
 One 0.33uF ceramic capacitor
 One 10uF ceramic capacitor (5mm lead spacing)
 Two 0.82uF film capacitors (must have lead spacing between 13mm and
16mm, voltage over 450VDC, and a capacitance above 0.5uF)
  One toroidal ferrite (most of these are also suitable)
 Two TO-247 compatible heatsinks
 Optional: one DIP-14 IC socket (DIP-14)
 Optional: two DIP-8 IC sockets (DIP-8)
 Optional: three terminal blocks (TB007-508-02BE)

Low voltage DC power supply

 One 12VAC transformer (this model is compatible with input voltages
between 110V and 240V)
 One bridge rectifier (most units that can handle over 25V and a few amps
will work fine)

High voltage DC power supply

 Two 250V electrolytic capacitors (over 500uF)
 One SL32 1 ohm thermistor (inrush current limiter)
 One bridge rectifier (minimum recommended current/voltage ratings of
10A and 1000V)
 Optional: one ON/OFF switch (more information below)

Total price: $70 (this includes shipping)

Other materials needed:
 Wire (including magnet wire for the secondary coil), pipe (for secondary
coil form), and miscellaneous hardware parts
 Soldering iron and solder
 Either the official PCB (details below) or breadboard
 Optional but useful: a handheld multimeter, oscilloscope, and Variac

Step 1: Order the materials

Listed above is every part needed to build a working half-bridge solid state Tesla
coil. However, please understand that the links provided may eventually expire.
If a part is unavailable, you are encouraged to look up and find a similar
replacement. Most of these part values are not super critical, and substitutions
can be easily made. Additionally, if you possess parts of similar values, feel free
to save money and use your parts instead! Owning a few large electrolytic
capacitors and a 14V power source could save you an extra $20. With all the
parts I had, I actually was able to build my SSTC for under $50!
These parts may also be found on other sites, such as digikey.com, newark.com,
and even Amazon, so feel free to hunt for better deals!
It is also worth noting that having a few extra components on hand isn’t a bad
idea. The components to worry about include the IGBTs, the UCC27425, the
74HC14, the 555 timer, and the high voltage supply’s bridge rectifier. The IGBTs
are the most likely item to break, followed by the bridge rectifier (the rectifier
typically dies from the overcurrent caused by IGBT failure). Minor screw-ups can
also lead to the IC chips blowing, and they are dirt cheap, so it’s smart to buy an
extra or two of each.

After you’ve settled on which parts to order, it’s time to start thinking about
what you’ll mount them on. I personally recommend the official PCB that I
designed for this circuit, but breadboard is also an option. The PCB should only
cost a few dollars, is thoroughly labeled, and highly user-friendly. For the
remainder of this instructional, I will be primarily talking about constructing the
circuit on this PCB.
To order the PCB, simply take the “SSTC PCB” .zip file downloaded with these
instructions and submit it to a PCB manufacturing website like JLCPCB.com.
This .zip file is technically referred to as a gerber file. If you want, you can
change how many PCBs you order (minimum with JLCPCB is 5 copies for around
$2 plus shipping), as well as the PCB color.
 Step 2: Wire up the circuit

This is the circuit we will be building; it’s basically the Loneoceans SSTC 2 circuit
with a few modifications. For one, I swapped the microcontroller-based
interrupter with a more traditional 555-timer circuit, as it is far more user
friendly and doesn’t require programming. I additionally changed and removed
a few other components, including the undervoltage protection part of the
circuit, after I found it was causing more harm than good. An NTC thermistor
was also added to the main power section to prevent dangerously high inrush
currents from destroying the rectifier and IGBTs. The need for this was actually
brought up by Brian from SciTubeHD, who learned himself by blowing several
components in his own copy of the Loneoceans SSTC 2.

How it works:
The driver for this coil works by first extracting a crude feedback signal from an
antenna near the coil and passes it by a two-diode array. As Power Max
demonstrated to me over a Zoom call, these two diodes essentially lock the
positive and negative voltage peaks of the AC signal to a set value, preventing
dangerously high voltages from entering the sensitive driver circuit.
Next, the signal passes through a resistor, capacitor, and 74HC14 Schmitt
trigger, which converts the somewhat sloppy signal into a more functional
squarewave that matches the resonant frequency. The new squarewave signal
is then pumped into the UCC27425 gate driver IC, where it is amplified.
Conveniently, our gate driver chip has something called an enable pin, which is
basically like its on-and-off switch. If we feed the interrupter’s signal to the
enable pins, we can control the Tesla coil’s pulse duration and frequency, and
therefore the spark appearance.
The resulting interrupted signal from our driver circuit is finally sent to a small
device known as a gate drive transformer, or GDT. Once properly assembled,
the GDT converts the single 12V signal from our driver into two 18 volts signals,
which are optimal for switching our transistors. If we phase the GDT correctly, it
will cause the transistors to switch the DC voltage from our power supply across
the primary coil at the resonant frequency. And since the resonant frequency is
detected by the drive circuit, we can stick basically any secondary coil in the
primary coil’s field and it will resonate almost perfectly, producing an extremely
powerful electrical discharge.

The power sections:

To power this circuit, we need two power sections: one for low voltage and
another for high voltage. All of the low-voltage circuitry is powered by a few
simple voltage regulators, which take any DC voltage from 14 to 24 volts and
adjust it and to fit the circuit’s needs. For our purposes, we can just take any
12VAC transformer and rectify it with a bridge rectifier to get around 17VDC.
For the high voltage input, this SSTC can take up to 400VDC. However, our wall
sockets can only give us around 120 volts or 240 volts AC, depending on where
you live. Fortunately, the circuit shown in the schematic takes care of this issue:
with the flick of a switch it can either function as a full bridge rectifier (to get
340VDC in 240VAC regions or 170VDC in 120VAC regions) or a voltage doubler.
The voltage doubler is only necessary for people in 110-120V regions, since
doubled 240V (680VDC) would simply annihilate the SSTC circuit.
FOR THE PCB: the 340VDC supply and 14-24VDC supply are off-board (a design
choice I made to save money on PCBs). For the low voltage supply, there is a
port for the raw 14-24VDC input, and for the higher voltage, there are two
positions to solder the power inputs to, as well as a ground port (marked ‘G’) to
connect to mains ground. REMEMBER! Only direct current can enter this PCB!
Here is a rough diagram to help wire up the PCB’s power and coils:
One final note: if you’re making this circuit without the PCB, make sure to
ground the low-voltage negative/neutral line. If you don’t, you’ll probably have
tons of issues with interference, even with good shielding.

Gate drive transformer (GDT) winding:

For the gate drive transformer, you’ll want to wrap two twelve-turn coils and
one eight turn coil onto a suitable ferrite core (more details about that in Step
3). Iron cores are almost non-functional at these high frequencies, so I advise
against using them. As you can see in the circuit schematic, the two twelve turn
coils are connected to the transistors with “opposing polarity” (they are 180
degrees out-of-phase). This is necessary for the transistors to switch correctly. If
you mess up the GDT phasing, the transistors will almost certainly die, so PAY
ATTENTION TO HOW YOU WIND THEM! My PCB takes care of the phasing for
you, and has marks to help indicate phasing. If you have a hard time
understanding this, all you have to do is:
 Step 3: Part Substitution and
Coil Setup

Perhaps one of the best parts about this circuit is its ability to handle changes
and customization. As mentioned before, a number of it’s parts don’t need to be
super exact, and can be changed for similar parts if need be. This section is your
guide to customizing the designs and making them your own.

Necessary parameters:
These are the general requirements for each circuit component. If you follow
what I say here, you should be good to go:
555 timer, 74HC14, and UCC27425: as far as I can tell, there are no suitable
replacements for these parts. If you are more experienced in electronics
designs, feel free to look around though!
Gate drive transformer (this is mostly regarding the ferrite itself):
 Initial permeability (μ): over 2000
 Diameter: around 20-30cm, it all depends on what you’re comfortable
winding. Larger toroids are typically easier!
 Recommended materials: 77, 75, and N87 are best, but 43 is also usable
 Wire: most thin, insulated wire. DON’T USE MAGNET WIRE! Magnet wire
will simply arc over, despite the low voltages.
Resistors:
 Power rating: most can be 1/4W (maybe less). The 6.8 ohm resistors
should be around 1 watt though, since they’ll be handling more power.
  Resistance: try to stay within a few kiloohms of the recommended values,
except for the 6.8 ohm resistors. For them, anything between 5-15 ohms
should work.

Capacitors:
 Voltage: should be above 25V for the low voltage areas. For the large
electrolytic capacitors in the doubler/rectifier, the voltage rating must be
250VDC or more. For the DC blocking capacitors in the power section near
the transistors, the voltage must be even higher: over 450V is needed,
and over 500V is recommended. This is because they will be experiencing
resonant voltage spikes, which can easily shred smaller 250V capacitors
(ask me how I know).
 Capacitance:
o For the small electrolytic capacitors (used in the low voltage
regulator section), any high capacitance (over 200uF) should work
o More than 500uF is recommended for the doubler capacitors
o For the small-value film and ceramic capacitors it’s best to stay
within range of the ratings given. Variation by 75% or more are
likely acceptable though.
o For the interrupter capacitor, you can honestly use any value you
want. Just be aware that it will affect your coil’s BPS and pulse
width. Lower values yield higher-BPS, thinner sparks, and higher
values give thicker, low-BPS sparks. A good range to experiment in
is 100pF to 100uF. I suggest using a value between 0.2uF to 0.5uF
because it works well with the potentiometers to give the widest
variety of spark appearances.
Diodes: most fast-recovery signal diodes will work
Bridge rectifiers:
 Reverse voltage: over 50V for the low voltage one (since it’s only handling
around 25V max from the transformer) and around 1000V for the high
voltage one
  Current: 4A or more for the low voltage one and 10A or more for the high
voltage one. Peak current rating for the high voltage one should also be
similar to or greater than that of the thermistor (25A or so is usually fine)

Transistors:
 Type: either IGBT or N-channel MOSFET, and should have an internal
diode. If no diode is built in, one must be added (look up info on flyback
or freewheeling diodes)
 Power: over 250W (over 400W if you plan to operate at higher BPS/duty)
 Voltage: 500V or more
 Current: less important, but I recommend over 10A
 Peak current: most important, should be over 60A

Linear voltage regulators (7812 and 7805): most 12V and 5V positive linear
voltage regulators that can output over 1A will work
Potentiometers:
 Power rating: 1/5W or more
 Resistance: anything you want, but, like the interrupter capacitor, it will
affect your coil’s output. For the 2M potentiometer, using a lower value
will increase the minimum BPS. For the 50K potentiometer, a lower value
will decrease the maximum pulse width (resulting in thinner sparks)
Thermistor: should be rated for around 1 ohm and over 20A
Coil setup and impedance (IMPORTANT!!):
For this circuit (and most IGBT-based Tesla coils), the resonant frequency
shouldn’t exceed 400kHz. Above 400kHz, the IGBTs may still function, but they
will do so with increasing difficulty and may wear down quicker and yield poor
coil performance. Since this coil is self-tuning, the resonant frequency is
determined by the secondary coil and its topload. By putting the design
parameters of your coil into a program like JavaTC, you can calculate the
resonant frequency, as well as some other important values, such as coupling.
With solid state Tesla coils like this, it best to leave the coupling below 0.4, with
best results around 0.3. If the coil is over-coupled, it will tend to arc over to the
primary coil, and if the coil is under-coupled, there will be less output.
One of the most critical aspect of your coil’s design is the primary impedance
(this is just a fancy term for AC resistance). If the impedance is too low,
excessive current will flow through the primary coil and kill your IGBTs, and if
the impedance is too high, your sparks will be noticeably smaller. For the IGBTs
I’m using, the primary impedance should be over 6 ohms in order to keep the
peak currents within the IGBT’s rating.
Calculating impedance can actually be pretty simple: just go to a website like
this that calculates LC impedance and input your coil’s specifications. The
inductance is that of your primary coil and the frequency is just your secondary
coil’s natural resonant frequency. Both of these values can be calculated using
our old friend, JavaTC. For the capacitance, you’ll just use the value of one of
our inverter capacitors. If you’re following my schematic, this value should be
around 1 microfarad. Once you hit calculate, the value you’re interest in is the
one marked ‘Total LC Impedance’. Once again, make sure you’re just over 6
ohms of impedance. In general, five turns on the primary is a good starting
point.
Step 4: Troubleshooting, Tips,
and Firing It Up!
While it’s totally possible for you to wire this circuit up and get it running well
on the first try, you’ll more than likely experience some bumps. Fortunately,
they are usually quite manageable and can be overcome with minimal effort.
Here are a few of my best tips for troubleshooting this circuit:
If there is no output:
 First, check all of your connections. I’ve been totally lost on several
occasions, and the culprit turned out to just be a bad connection
 Try bringing the feedback antenna closer to the coil. I’ve found my coil
works best when the antenna is within a foot (30cm) or so of the
secondary coil
 Test your power sections and make sure they are getting (and giving!)
power
 If tons of current is being pulled, it’s possible you wired your GDT wrong
and killed your IGBTs. You may have killed them in other ways, but this is
the most common way. It’s also possible there is a random, accidental
short somewhere in the circuit
If the output is very weak:
 Try swapping the primary coil connections. This almost always solves the
issue
 The antenna might not be close enough, try moving it closer
 Check the interrupter on/off switch. I’ve had times when it was open (no
interrupter signal being fed), and there was enough residual
charge/interference to run the coil, albeit in a weaker state. This problem
is usually indicated by a continuous, fuzzy plasma discharge (no buzzing or
pulses)
  Check the secondary coil’s ground connection. If a coil isn’t properly
grounded, the voltage differential at the top could be lower with respect
to ground, and therefore yield weaker output
 Your coupling could be very low or your primary impedance could be
extremely high. Try running some calculations and see if anything jumps
out as strange or off
If you have unstable output (uneven BPS or pulse width)
 This is usually a result of interference. Make sure your PCB’s ground
connection is good, or, if you’re building it without the PCB, make sure
the low voltage negative/neutral is grounded. Also, try shielding the
circuit with a layer of grounded metal or metal foil

Crank it up!
Once the design, assembly, and troubleshooting are out of the way, it’s time to
fire up this circuit and give it a run for its money! When built properly, this
circuit can easily produce sparks larger than the secondary coil itself. With my
unit, I’ve been able to achieve 12” sparks from an 8” coil, and 14” sparks with a
similarly-size coil. These results are comparable to many of the commercial
Tesla coils you can buy. The only difference: this coil is far more versatile and it
costs less than half the price!
The sparks can also take on a variety of appearances based on how you set the
interrupter. With a low BPS and pulse width, the sparks resemble those of a
voltage multiplier or Van De Graaff machine. With ultra-long pulse width, the
sparks look almost like fire or the output from a microwave oven transformer.
And by raising the BPS and lowering the pulse width, you can create everything
from thick, vacuum-tube coil type bolts, to angry, spark gap coil-style lightning.
Not getting the spark lengths you hoped for? Here are some pro tips for getting
the largest sparks possible from your design:
 Raise the coupling as much as possible without it losing energy to coronal
discharge and intercoil arcing
  Use fewer turns (and therefore a lower impedance). Remember though, 6
ohms is just about the minimum impedance this circuit can handle (unless
you get some REALLY powerful IGBTs)
 Add a topload. This can DOUBLE the output size, especially if you use a
smaller breakout point. Make sure to use a breakout point, otherwise the
resonant voltage rise will become too great and intercoil arcing will likely
result (along with feedback to the primary circuit, and possible transistor
damage)
 Crank up the Variac and boost the voltage from 340VDC to 400VDC

Music mode
One of the most iconic feature in modern Tesla coils is their ability to play
music. This is usually done by applying a music signal in place of the
monotonous interrupter signal, causing the sparks’ BPS and pulse width to vary
in the same way a speaker does when it plays audio. Although it’s not depicted
in the circuit diagram, I added a port on the PCB specifically for custom
interrupter signals. If you switch off the main, on-board interrupter (this is
necessary; if you don’t, the 555 timer will blow) and apply a 12V squarewave
music signal, the coil will come to life playing the corresponding tune! In my
accompanying YouTube video, I use an Arduino-switched 12VDC supply to
musically interrupt my coil, but the audio quality was pretty bad, since the duty
was fairly high (50% or so). For best results, use a lower pulse width signal! One
possible candidate for a musical interrupter is the humble MP3 player: simply
take the headphone output from the player and use it to switch a transistor,
which will in turn switch some 12V power source which will be fed into the
PCB’s music port.