Design of Solid State Tesla Coil With Music Playback Functionality

This paper presents the design, simulation, and implementation of a solid state Tesla coil (SSTC) with music playback functionality through its arcs. It showcases various circuit designs that explore both feedback and non-feedback-based control mechanisms. The non-feedback based mechanism relies on an external oscillator circuit based on NE555 timer IC to drive the Tesla transformer coil at its resonance and the feedback based system relies on the selective amplification of a certain frequency at which the secondary coil is self-resonant. Additionally, to produce tones from the Tesla coil’s arcs, this paper implements a fixed gate signal interrupter circuit design that produces specific tones, as well as a music-based gate signal interrupter circuit design that produces music from the arcs. To verify the functionality of the design, the designed circuits were simulated in the LTspice SPICE simulation software and then implemented on a prototype board followed by a four-layer printed circuit board implementation. The primary coil of the Tesla transformer was controlled using an insulated-gate bipolar transistor (IGBT) based half bridge circuit.


I. INTRODUCTION
Tesla Coil, originally invented by Tesla, works on the principle of resonance between the secondary coil of a transformer and the parasitic capacitance of the coil [1].This parasitic capacitance includes the winding capacitance and capacitance between the top load and ground [3].The transformer first steps up the voltage to a few kilovolts, which is further amplified due to resonance to hundreds of kilovolts (≫100 KV).The transformer's secondary coil is in the shape of a tower with a high secondary-to-primary turn ratio.On the primary side, a much lower voltage than the secondary is injected at the resonance frequency of the secondary.To do so, it uses a combination of a capacitor, a primary coil as an inductor, and spark gap.This design was also termed the spark-gap Tesla Coil [5], [8], [9].
This paper presents the design of a SOILD STATE Tesla Coil that eliminates the need for a spark gap [6], [10].To do so insulated-gate bipolar transistors (IGBTs) are used as switching elements with some extra driving circuits [11].
The associate editor coordinating the review of this manuscript and approving it for publication was Ye Zhou .
For this purpose, various circuits have been designed which serves different purposes.This includes a non-feedbackbased approach that uses a 555-timer IC to create a basic square wave at the resonant frequency of the secondary coil of the transformer.This basic wave passes through various Schmitt triggers and RC logic to produce the final driving waveforms.Another approach uses a feedback antenna that feeds a portion of the high voltage output signal back to the logic to continuously drive the IGBTs.To add more functionalities to this approach, circuits that interrupt driving signals were designed.These include a fixed interrupter and music-based interrupter.The designed fixed interrupter serves two purposes.One is to reduce the power consumption of the entire system and the second is to change the shape of the output arcs produced.The music interrupter interrupts the drive signals with respect to the music signal to produce music from arcs.

II. BACKGROUND
Tesla coils have been implemented by many researchers in their own ways.Their work built a foundation for the Tesla coil design presented in this paper.Here, we list a few important works highlighting their contribution which laid the foundation of the work presented in this paper.
Tesla [1] presented an apparatus to transmit electrical energy.This apparatus design was then later termed as ''Tesla Coil''.In the patent, Tesla presented the design of a transformer with a self-resonant secondary coil in the form of a tower with a toroidal top load of a large surface area to prevent charge leakage, which when exited from the primary side at the resonant frequency of the secondary coil produces maximum charge displacement at the surface of the top load.This implies that to create lighting arcs, a pointy metallic surface is required at the top load.This was also confirmed in [29].
Costa [2] explained the cause of the unusually high voltage at the secondary end of a Tesla transformer.When a pulsed input is applied to the primary coil, the response of the system at each rise and fall edge is added and hence an effective sum is observed at the output of the secondary coil.In addition, the reduction in the resonant frequency of the secondary coil was proportional to the increase in its parallel capacitance.The parallel capacitance of a secondary coil can be altered by changes in the surrounding environment and the dimensions of the coil.
Craven et al. [3] added to the knowledge on this parallel capacitance by introducing its components.This capacitance is the equivalent sum of the self-capacitance of the secondary coil, capacitance of a field grading electrode connected at the top of the secondary coil, and capacitance due to the surroundings.The work then focuses on improving the spectral purity of the Tesla coil using helical cavity filters.These filters reduced the magnitude of the currents at higher mode frequencies while the fundamental current amplitude remained largely unchanged.
The next important consideration is the design of the high voltage transformer.Conventionally, an air-cored transformer is used in a Tesla coil.This is because, the air-cored transformer does not have the problem of magnetic core saturation, hysteresis loss, and eddy current loss.However, their coupling coefficient is close to 0.6.This restricts the maximum attainable output voltage and reduces efficiency.Basak et al. [4] solved these issues by employing a magnetic core with high saturation flux density and low hysteresis loss.Metglas 2605SA1 was used as the core with fine laminations to reduce the eddy current loss.This core was also used as a pulse-forming line (PLF) to achieve compactness.A circuit with a single IGBT as a switch was used to drive the transformer, which provided pulses of energy to the coil.
Jana et al. [15] further discusses various design parameters for constructing a spark-gap based tesla coil.The design of the primary coil, secondary coil, top load, spark-gap, input power transformer, and other related parameters are discussed.The selection of a conductor for the primary side of the tesla-transformer plays a vital role in reducing the losses.The differences between silver-plated conductors, copper tubes, Litz wires, and solid wires were elaborated.The copper tube is the most widely used conductor because it is commercially viable and at the same time helps to reduce the corona loss due to its smooth surface.The shape of the primary coil, namely, flat spiral, helical, and inverse conical, is an important consideration in the design.It was found that the current density magnitude was very high in the helical coil whereas it was the lowest in the flat spring coil.Helical type primary coil can produce very high power, however, in the long run, it can degrade the efficiency of the Tesla coil.The highest ohmic loss and electric field strength were observed in the helical coil because of its highest current density.The least was observed in the flat spiral coil.Hence, a suitable selection between these types considering the tradeoff between the power, and ohmic losses is required.For the design presented in this paper, a helical coil design was used.
Rahman and Khan [5] designed a USB powered spark-gap based tesla coil using a high voltage source of ∼1kV from a commercially available bug zapper.The spark gap-based design is based on the principle of parallel LC resonance.The circuit consists of the primary coil of the Tesla transformer as an inductor(L), capacitor bank(C), and spark gap electrodes connected in series.The distance between the electrodes is such that at a certain high voltage, the air, that is, dielectric breaks down connecting the capacitor and inductor in parallel.When the capacitor banks are charged sufficiently through the high voltage source, the dielectric breakdown of the air between the spark gap effectively causes the inductor and capacitor to connect in parallel.This excites the energy transfer between the capacitor and the inductor (i.e., the primary coil) at the resonance frequency causing LC resonance.The transformer increases this voltage due to its high turn ratio.Furthermore, due to the resonance at the secondary side, due to parallel parasitic capacitances, the voltage attained at the top-load is further amplified.
Older designs of the Tesla coil are based on the spark gap and relies on high input voltage to creates sparks in this spark gap for the primary side resonance to occur.Soleyman [6] discussed methods for designing a solid-state Tesla Coil (SSTC).This eliminates the need for a resonant primary circuit in SSTC.The paper discusses the use of a half bridge design using metal-oxide-semiconductor field-effect transistor (MOSFET) to drive the primary coil.Further, the paper discusses the challenges of driving the half bridge and the use of transformer-coupled gate drive circuit to overcome them.It is important to select a suitable transformer with a suitable core to drive the gates of the MOSFETs so that it does not exceed the saturation flux density of the chosen core.The selection of gate resistor plays a crucial role because it lowers the maximum overshoot voltage but at the same time can also increase the switching time.A voltage overshoot at the gate can destroy the MOSFET and a high switching time can effectively reduce the on time of the pulse applied to the primary of transformer.Hence, a suitable selection that considers the tradeoff between the overshoot and switching time is important.
Teraguchi and Minami [7] discussed a similar half-bridge design for driving a Tesla transformer.Furthermore, their work focused on the pulse repetition frequency (PRF) method to generate music from the output.This method interrupts the oscillator signal based on music data to generate the drive signals for the half-bridge.The design uses a precision oscillator to generate the oscillator signal and an Arduino microcontroller to generate a music signal based on a keypad input.A gate drive IC was used to drive the half-bridge.
Obeidat et al. [8] present a design of audio modulated dual resonant solid state tesla coil.The design used a full bridge (H-bridge) to drive the primary side.In a dual resonant system, the primary side is also made resonant which effectively increases the efficiency and the output voltage of the tesla coil.The design uses a slayer-exciter feedback approach which supplies the feedback current to the gate of the IGBTs.An Arduino microcontroller was used as a safety switch to interrupt the function in the case of IGBT failure.This design was tested at a low voltage of 15V which did not produce significant arcs at the top load.
The currently published literature on the design of a Tesla coil focuses mainly on the physical design of the Tesla coil and very little on the driving methodology.Drive signal generation circuit design has not been thoroughly addressed in the literature.Many of these studies utilized a simple sparkgap-based approach to drive the Tesla coil, which requires a high input voltage in the range of a few ∼kV to cause a dielectric breakdown.A more efficient way to drive these Tesla transformers is by using semiconductor switches instead of a spark gap, as described in [6], [7], and [8].Thus, a much lower voltage of around ∼80v could be used to a produce significantly large output at the top load.This also enables the use of advanced modulation techniques for the drive signals of semiconductor switches in which the length, shape, and musical tone of the arcs can be altered.
The work presented in this article is of significant importance due to the following reasons, 1. Musical solid state tesla coils are a comparatively new research topic with limited published literature.2. The driving circuit of a half-bridge has not been sufficiently discussed in literature.This paper discusses the driving circuit in detail with the support of LTspice simulations.3. Soleyman [6] used a lab bench function generator as the oscillator to simplify the design, however, this is not a commercially viable solution.Teraguchi and Minami [7] used a discrete precision oscillator circuit but their design was not described.This paper discusses the design of such an oscillator circuit in detail.4. The design steps to avoid half bridge hazards such as the short circuit of high voltage power rails and overshoots are described in detail in this paper.5. Teraguchi and Minami [7] used a microcontroller to generate a preprogrammed music output signal which is essentially a square wave.However, a pure audio signal is sinusoidal, which is the output signal type of many commercial devices, such as audio players and mobile phones.The design presented in this paper uses sinusoidal music output from the audio jack of a mobile phone to generate the required music-interrupt signal using operational amplifiers (OPAMPs).6. Obeidat et al. [8] tested their SSTC apparatus at a low voltage of ∼15Vdc which did not produce arcs at the top load.The output arcs are one of the key features of tesla coil.Testing at higher voltages requires additional tuning and protection from half bridge switching hazards as discussed in point 4.This paper presents the design which was tested at a much higher voltage of around ∼100Vdc and produced significant arcs at the top load.In summary, this paper comprehensively describes the design of such a musical solid state Tesla coil that overcomes the shortcomings of previously published literature.The design presented in this paper is also supported by simulations of individual sections of the designed circuit using LTspice SPICE simulation software.This also makes this design more commercially viable.

III. DESIGN METHODOLOGY A. BASIC FUNCTIONAL BLOCK DIAGRAM
Figure 1 shows a basic block diagram of the system implemented in this paper.The drive signal generation block generates IGBT drive signals, which are then used to drive the IGBTs with the help of gate drive ICs and gate drive transformer (GDT) [12], [14].This drive signal was interrupted using a fixed and a music-based interrupter to produce the desired results.Subsequently, using a different circuit, feedback from the secondary coil was used to drive the IGBTs at the resonance of the secondary coil.The design of the different blocks is discussed in detail in the subsequent sections of this paper.For convenience, it is discussed backward, that is, from the Transformer to Interrupter.

B. TRANSFORMER
The Transformer consists of a primary coil, secondary coil, and top load as shown in Figure 2. The design of the transformer coil is critical because it determines the resonance frequency [15].The arcs behave differently at different frequencies.
The resonance frequency of the secondary coil is given by, where, F r is the resonant frequency of the secondary coil, L is the inductance of the secondary coil, and C para is the parallel parasitic capacitance of the coil [3].
The inductance of any cylindrical coil can be estimated as [16], where, L is the inductance of any cylindrical coil, N is the number of turns, r is the radius of the coil, l is the length of the coil, µ o is the permeability of free space (1.26 × 10-6 m kg s −2 A −2 ), and µ r is the relative permeability (for air at standard temperature and pressure µ r is equal to 1.0006).
The main component of parasitic capacitance is the capacitance between the top load and ground and is highly dependent on the surroundings as the relative permittivity of air changes with temperature, humidity, and atmospheric pressure [17].It generally lies between 1-10pF and is determined experimentally.
The primary coil was constructed using six turns of 5mm copper pipe to carry high currents.The secondary coil consisted of approximately 1600 turns of 36-gauge enamel copper wire wound around a 2-inch 20cm long white PVC water pipe.The estimated inductance of the secondary is 32.62 mH.The Top Load was constructed by covering the custom 3D printed design of the top load with aluminum tape.The purpose of the top load is to increase the parasitic capacitance which in turn lowers the resonance frequency of the secondary coil [2], [3].
The entire structure was supported by a custom 3Dprinted support structure designed in Fusion 360.The design of the support structures and the top load are shown in Figure 3.

C. GATE DRIVE TRANSFORMER (GDT) DRIVER AND GDT
IGBTs are driven through a Gate Drive Transformer (GDT) for the following reasons: • The IGBTs are switching high voltages, therefore, to turn on the upper IGBT in a half bridge configuration, we need a gate voltage higher than the emitter voltage which is not possible with direct driving methods.
• To solve this issue, an IGBT driver with a bootstrap circuit is typically used.However, such ICs cannot be used at very high voltages.
• A GDT will also provide isolation between the high voltage and the driver.Two gate driver ICs (TC4420) were used to drive the GDT, as shown in Figure 4.The GDT is connected to J7. Complementary capacitors and pull-down resistors were added as recommended in the datasheet of the IC [18].Diodes D7, D8, D9, and D10 were used to clip the drive voltage to +15V and 0V.The GDT was constructed using eight turns of enamel copper wire for each coil (a total of three coils) around a 3mm diameter ferrite core.
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D. IGBT-BASED HALF BRIDGE DRIVER
A typical Half Bridge configuration is shown in Figure 5.The GDT drives the gate of the IGBT through a 10 -10W resistor to limit the current.Diode D11 and D14 are used to decrease the turn-off time of the IGBT by discharging the internal gate capacitance of the IGBTs faster, and Zener diodes are used to clip the voltages to ±15V.The IGBT FGL60N100 was used because it can handle a high reverse voltage of 1000V and a forward current of 60A [19].
The gate resistance was determined as follows: The total gate charge provided by the IGBT's datasheet was 275nC [19].It was assumed that the switching frequency of the IGBT is 800KHz.This implies the on-time pulse period is 0.625 µs.To minimize the rise and fall times of the applied pulse, the IGBT should be turned on and off as fast as physically realizable without causing any ringing or overshoot [13], [20].Assume to turn it on within one-fifth of this time, that is, 0.125 µs.
The current is given by where, I is the current, Q is the total charge to be transferred, and t is the time period within which the charge needs to be transferred.
On calculating, the current comes out to be 2.2A.For this, a resistance of 6.82 is required at 15V.A lower value decreases the rise time because the charge required to turn on the IGBT is delivered faster.However, it can increase the amplitude of unwanted oscillations (ringing) due to resonance between the inductance and the gate capacitance [20].Hence, a value of 10 was ultimately chosen because it is a standardvalued resistor.
Capacitors C36, C37, and resistors R22, and R23 create a mid-voltage to drive the primary coil in the +40 to -40V range (if powered with 80VDC).Thus, eliminating any DC components across the primary coil.
Additionally, Fast Diodes MUR1560G [21] (D17, D18 in Figure 5) were used to dissipate the energy of the coil when both IGBTs were off.

E. DRIVE SIGNAL GENERATION
Figure 6 shows the circuit to generate the main clock which will be further used to generate gate drive signals.Here, NE555 timer IC is configured in astable multivibrator mode to produce a square wave of adjustable frequency (around 730KHz, which is the resonance frequency of the secondary).Diode D2 charges the timing capacitors (C11, C12) faster to achieve a 50% duty cycle [22], [23].
The frequency of the clock generated is given by, where f is the frequency of the clock generated, R a & R b are the resistances (part of the potentiometer VR1), and C is the timing capacitor's capacitance (the combined capacitance of C11 & C12).And, the duty cycle of the clock pulse is given by, To achieve a 50% duty cycle R a should be equal to R b which is the case in the designed circuit.
On the reset pin (pin-4 of U1), an interrupt signal can be applied through a 1K resistor to interrupt the produced clock as desired.This pin can also be connected to +5V for continuous clock generation.
This clock signal is then sent to a series of Schmitt Triggers and an RC-D circuit to produce the drive signals for the IGBTs.
Six inverting Schmitt triggers were used here which are part of the 74LS14 IC [24].These six Schmitt triggers are named U4 * (A to F) in the schematic shown in Figure 7.The first Schmitt trigger (U4A) acted as a buffer for further stages.Because we have two IGBTs (in the Half Bridge), it requires two different drive signals that should be complementary to each other as we do not want both the IGBT to turn on simultaneously (as that would short the high voltage power rails).In fact, we desire a small delay between the drive pulses to ensure that both IGBT will never turn ON simultaneously.Now upon following the first drive signal circuit, an RC network with a diode can be observed.Here the RC network acts as a charge-discharge circuit where when the input clock is positive, the capacitor charges slowly but when the input clock is zero, the capacitor discharges through the diode almost instantaneously, thereby, reducing the on-pulse width after passing through the Schmitt trigger stage.
The reduced pulse width is given by, where, T reduced is the reduced pulse width, T on is the original on-pulse width, RC is the time constant obtained by multiplying the value of resistance and the capacitance of the charge-discharge circuit.Thus, a reduction of 300ns in the on-pulse width was obtained at the output.This value can reduce as per the hysteresis of the Schmitt trigger.This reduced on-pulse width signal passes through another set of Schmitt triggers to achieve the final signal.This process is the same for the second drive signal circuit.The only difference is that the clock is inverted using another Schmitt trigger in the beginning.
If an interrupt signal is injected, the clock from the 555 IC will be halted.This means that the first drive will have a high output and the second will have a low output.However, we desire both drive outputs to be low when an interrupt signal is injected.Hence, a buffer IC (74HCT241) with an enable pin (pin-19) was used [25].The enable pin will get low when an interrupt signal (i.e., a low pulse) is injected.This disables the first drive output ensuring that both drive outputs will be low when the interrupt signal is injected.This drive signal is then provided to the gate driver IC (pin -2) as shown in Figure 4.

F. FIXED INTERRUPTER / TRIGGER WITH ADJUSTABLE INTERRUPT DURATION TO PRODUCE A SINGLE OUTPUT TONE
When the inaudible output arcs are interrupted in the frequency range of 20Hz to 20KHz, the arc produces a specific tone according to the frequency.The output arcs can be interrupted by interrupting the drive signals of the IGBTs.An interrupter clock that produces an output frequency of less than 1KHz was designed.The duty cycle of this interrupter signal could be varied by adjusting the potentiometer.The power consumption of the system and the output arc strength can be analyzed at different duty cycles.
For this, another NE555 timer IC was used to generate the interrupt signal with a variable duty cycle as shown in Figure 8.The duty cycle of this interrupter can be adjusted by adjusting the 10K potentiometer which in turn affects the output arcs and power consumption.Although, it also disturbs the frequency but this can be ignored since the time of off-pulse is important.The output interrupt signal is observable on the netlabel Trig_fixed.

G. MUSIC-BASED INTERRUPTER
The circuit for generating interrupt signals whose pulse width and pulse interval changes based on the music input is shown in Figure 9. Different frequency components of music have different pulse widths and intervals.This circuit generates a square interrupt pulse based on the frequency of sinusoidal input signal.The music input was provided through an Auxiliary cable connected to the netlabel AuxIN and the generated interrupt signal was available at the netlabel Trig_Music.The output from the aux was approximately 0.8Vpeak so an amplification stage was used in the beginning.It also uses a different 5V supply to isolate noise.
The first OPAMP (U7A), is configured as a non-inverting amplifier whose gain is given by, where, A f is the Output Gain, R f & R i are the feedback resistances (i.e., R8 and R10 in Figure 9).This amplified the input music signal by a factor of 3.2 which was then fed to another OPAMP configured as a comparator to output pulses based on the reference voltage set by a potentiometer on the non-inverting terminal of U7B.A transistor stage was also used at the output to amplify the current.
The reference voltage is given by, where V REF is the reference voltage at pin-5 of U7B, R a and R b are the resistors to set the reference voltage (i.e., VR3 and R14 in Figure 9, respectively).And the output from the U7B OPAMP at pin 7 is given as where, V o is the output voltage at pin-7 of U7B, and V − is the voltage at inverting terminal of U7B (pin-6).This interrupt signal is then fed to the reset pin of the main clock (U1 pin-4, See Figure 6) through a resistor.The main clock starts or terminates the oscillations based on the signal voltage level.If the interrupt signal is high (i.e., 5V), the main clock starts oscillating at the resonance frequency of the secondary of the Tesla transformer thereby producing arcs at the top load.If the interrupt signal is low (i.e., 0V), the main clock's oscillation is terminated which also terminates the output arcs.This production and termination of arcs at the frequency of input music creates sound from the arcs with musical characteristics similar to those of the input music.

H. FEEDBACK CIRCUIT
Figure 10 shows the feedback circuit used to drive the SSTC without manually generating the clock signal.When the complete system is powered on, assume that the antenna receives a low signal, which means that the nets, Drive1, will be low and Drive2 will be high (due to inverting Schmitt triggers).This powers the primary coil such that in the next phase, the antenna receives a high.This means Drive1 will be high and Drive2 will be low.This powers the primary coil in the opposite direction and thus in the next phase, the antenna receives a negative pulse which is clipped to 0V using diodes D19 and D21.This cycle continues at the resonance frequency of the secondary coil.The driving nets (Drive1 and Drive2) This means that with this addition we do not require manual adjustment the clock frequency and hence, the need for the main clock 555 timer circuit (shown in Figure 6) is eliminated.

I. POWER SUPPLY
The complete system uses 3 different voltages to operate.These are the following, • +15Vdc: This is the main input voltage to operate GDT driver ICs.To operate the timers and digital logic, it was converted to +5V using a voltage regulator.
• +5Vdc: This voltage was created from +15V using the LM317 voltage regulator to power the 555 IC and digital logic.The circuit used is shown in Figure 11.
• +40 to +340Vdc: This variable DC supply was created using a Variac and a full bridge rectifier circuit with capacitor banks at the output.This supply was used to operate the primary side of the tesla transformer through the half-bridge.In Figure 11, using a 680 resistor at R4, 5Vdc was achieved at the output.Diode D1 is used to discharge the output capacitor C3 when the input +15V is unavailable (as per the datasheet) [28].
Here, the regulated output voltage is given by [19], where, V o is the output voltage, R a & R b are the resistances to set the output voltage (i.e., R2 and R4 in Figure 11), V REF is 1.25V,I ADJ is 50µA (can be neglected [19]).

IV. SIMULATION RESULTS
The designs were simulated in LTspice to verify the functionality.These simulation results are as follows: A

. DRIVE SIGNAL GENERATION WITH FIXED INTERRUPTER
In Figure 12, the LTspice simulation circuit is shown, where the first (top) 555 IC is to generate the main clock at the resonance frequency of the secondary coil.The lower 555 IC was used as a fixed interrupter.The circuit is similar to that discussed in Figure 6, 7, and 8.  Figure 13 shows the simulation output of the generated drive signal without interruption.Note that both the drive outputs (represented in red and blue) are complementary to each other with a dead time between them so that the two IGBTs would never turn on at the same time to create a power rail short.The circuit works as expected, as explained in earlier sections.
Figure 14 shows the result of the two drive signals with an interruption of 2ms.As expected, the two drive signals were interrupted every 2ms.Note that when the signal was interrupted, none of the drives showed a high output even though both outputs were complementary to each other.This is because of the used buffer IC with the enable pin, as explained in earlier sections.The buffer with enable is implemented with an AND gate in LTspice to verify the design.

B. MUSIC-BASED INTERRUPTER USING OPAMP AND SINGLE SUPPLY
Figure 15 shows the LTspice simulation circuit, which is similar to the circuit shown in Figure 9.Here for the music source, a simple 100Hz sine wave was used.The outputs of the simulation at various stages are shown in Figure 16.Note these observations at different stages of the circuit, • At SignalInput: Since this node is biased with a voltage divider at 2.5V.It can be observed that the signal swings around 2.5V to 2.5 ± 0.8V • At AmplifierOutput: The signal is amplified perfectly 3.2 times to achieve a 5Vpeak output.
• At PWMOutput: A PWM wave can be observed at the comparator stage output.The initial unevenness of the output was due to the charging of the bias capacitors.
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C. FEEDBACK CIRCUIT
Figure 17 shows the basic simulation circuit used to simulate the feedback.Note that the following parameters were taken for granted in the LTspice simulation circuit design, • 2N3904 BJTs were used for simulation purposes.
In reality, 60N100ND1 IGBTs were used with gate drivers and GDT circuits as discussed earlier.
• VCC used was much higher than 10v during implementation.About 60-340Vdc.
• Voltage sources V4 and V5 were used to create ''Mid'' Voltage.In reality, capacitor banks of 660uF were used in the same fashion.
• A transformer coil was used as the antenna in the simulation.A small piece of wire was used as a crude antenna during implementation.From Figure 18 it can be observed that the antenna receives a signal of approximately ±12V which is then clipped to 0-5V using clipper diodes.This signal then passes through a set of inverting Schmitt triggers to drive the two transistors, which then drives the primary coil.As discussed earlier, a simple interrupt pulse was injected before the Schmitt triggers through a diode and a resistor to interrupt the feedback.This also worked as expected.Note that the output voltages reach 800Vpeak with an input voltage of just 10Vdc.This is known as resonance amplification.

V. IMPLEMENTATION
The circuit design was implemented on a perfboard (Prototype Board) followed by a printed circuit board (PCB) implementation.Figure 19 shows all the components of the system with labeling.After verifying the crude implementation on a perfboard, a 4-layer printed circuit board (PCB) was designed using Altium Designer.The top and bottom layers of the PCB were used to route the signal and power, and the inner two layers were used as ground planes.Figure 20 shows the fully assembled PCB.
This PCB is responsible for generating the IGBT drive signals and has different options to switch between a fixed interrupter and a music-based interrupter using the short jumpers provided on the PCB.It can take music input through an auxiliary cable to produce music from the output arcs.Figure 21 shows the complete setup with the PCB.The PCB was powered with a 12-15V DC supply and the high DC voltage for the half-bridge was provided through a Variac (Variable Transformer) and rectifier circuit.
On the top of the top load, a nail was attached as a sharp object through which the electrons will eject out.This is because electric field strength is maximum near the metallic edges [29].
Appropriately sized heatsinks were used for the two IGBTs of the half-bridge.

VI. TUNING
To tune the system to the resonant frequency of the secondary coil, the following steps were followed, 1.First, the system was set up in no-interrupt mode by adjusting the short jumpers provided on the PCB. 2. The PCB was then powered with 12Vdc and the IGBT with 100Vdc.3. Now the potentiometer VR1 was adjusted till arcs were observed at the output.4. If no arcs are observed, capacitors C11 and C12 are adjusted.An additional capacitor of 0.01 µF was added in this case.Then, Step 3 was repeated.5.After the arcs were observed, other features, including the fixed interrupter and music interrupter, were verified.
After tuning the circuit, the frequency produced by the main clock was measured using an oscilloscope.The measured frequency was around 730KHz which was the resonant frequency of the coil.

VII. RESULTS
The results shown in parts A and B were measured using a Hantek 100Mhz digital storage oscilloscope.

A. MAIN CLOCK SIGNAL @ ∼730KHz
The uninterrupted clock signal generated using the 555 IC is shown in Figure 21.The frequency of the generated signal was precisely calibrated to produce a ∼730Khz ∼50% duty cycle square wave through the potentiometer.
It was also found that the square wave with duty cycle within the range of 40% to 60% yielded arcs at the output and absolutely no arcs were observed outside this range.Therefore, precise tuning is important.The arc length also decreases if the frequency of the square wave deviates more than 10KHz.

C. PRODUCED ARCS AT 100Vdc AND DIFFERENT INTERRUPT DUTY CYCLES
The output arc characteristics were observed at different interrupt duty cycles and at a constant rectified DC voltage of 100V.Note that the circuit was powered at 12.1V as shown in the figures below.The results for the two different duty cycles are listed.
As shown in Figure 25, at 50% interrupt duty cycle, the arcs appear more clustered and not individually distinguishable.Moreover, the current consumption of the circuit was approximately 170mA (which includes only the current consumption of the driving circuit, not the current consumed by the transformer from the 100Vdc rectifier output).
As shown in Figure 26, at 20% interrupt duty cycle, the arcs become less clustered and are more individually distinguishable.Notably, the current consumption was reduced by 100mA (i.e., 59% reduction in current consumption).
In addition, because the interruption frequency (∼1KHz) is in the audible frequency range, a distinct sound from the arcs is heard which changes with the change in frequency and duty cycle.

D. ANALYSIS OF OUTPUT MUSIC THROUGH SSTC's ARCS
When the fixed interrupter was replaced with the music-based interrupter, saturated but clearly understandable music was heard from the arcs.
To mathematically analyze the similarity between the output music and original music, we analyzed the frequency components of the output signal and the correlation between these two signals using MATLAB.Two different music signals (Music A and Music B) of approximately 30s duration were given to the music-based interrupter circuit through an Android smartphone and the output music through the arcs was recorded.An analysis of the recorded output music signal versus the original music is presented below.• Music A: Imagine Dragons-Bones From Figure 27, it is observed that the higher frequency components of the original music (554.3Hz,622.1Hz, 698.4Hz) are present in the recorded music with some higher harmonics.The lower frequency components (less than 200Hz) got vastly attenuated.
TABLE 1 shows the correlation matrix obtained using the ''corrcoef'' command in MATLAB.A correlation of 0.0785 existed between the original and the output signals.This implies a weak but positive correlation between the two signals, confirming the presence of the input music in the output arcs.
• Music B: Shiva Theme (From Brahmastra Movie) A similar result can be observed in the analysis of this music from the arcs of the SSTC in Figure 28.The lower frequency components of original music (below 200Hz) are vastly attenuated and the higher components, that is, 554Hz, 615Hz, 936Hz, 993Hz, and other related harmonics, can be observed in the output music.
A slightly improved cross-correlation between the music from the output arcs and the original music is observed in TABLE 2. A positive cross-correlation proves presence of the original music in the music from the output arcs.The same was also observed when listening to the original and output music from the arcs.

VIII. APPLICATIONS
Musical solid state Tesla coil have variety of applications.Some of these applications are described below, • Musical SSTCs have been used in the entertainment industry in the past.They have been used to entertain crowds with visually stunning arcs that are synchronized with music.Their widespread use may be limited by the lack of published design articles.
• A cost-effective, and compact version of the musical solid state Tesla coil design can be used as a desktop entertainment device for consumer-based applications.
• A solid state Tesla coil can serve as a cheaper alternative for producing arc pulses for electrostatic discharge (ESD) related testing of devices.
• In education, musical SSTC can be used to demonstrate the resonance and modulation of high voltage arcs to produce music.
• In future research, more aspects of the design can be improved.One potential area of research could be improving the output spectrum, and correlation of music from output arcs with original music.Various advanced modulation techniques can be implemented in the future.

IX. CONCLUSION
In summary, this article presents the design of a solid-state Tesla coil using IGBT based half-bridge.This half-bridge was controlled using a gate drive transformer with the required current limiting and voltage clipping circuits.The half bridge switches the primary coil of the high voltage transformer at the self-resonant frequency of the secondary coil of this transformer.Two different control approaches, feedback and non-feedback based, were discussed.The feedback-based approach feeds back a portion of output of the high voltage transformer using a wire antenna whereas the non-feedback approach relies on an oscillator circuit pre tuned to the self-resonant frequency of the secondary coil.In addition, circuits for the IGBT gate pulse interruptions were designed.This includes a fixed gate pulse interrupter circuit to produce a specific tone from the arcs and a music-based interrupter circuit to produce music from the arc.The design was simulated in LTspice, followed by its implementation.The simulation results are verified using an oscilloscope.Subsequently, the produced arcs and power consumption were observed at different percentages of the interrupter duty cycle.At a low interrupt duty cycle, the individual arc traces are more distinguishable and the circuit consumes less power.Finally, the music playback functionality was tested using input music from an Android smartphone.The frequency content of the music in the arcs from the top load was analyzed, and its correlation with input music was determined using MATLAB.A positive correlation was observed between the original music and music output from the arcs.This work provides a unique approach for designing a Tesla coil compared with a traditional spark-gap-based approach.Furthermore, this article provided a clearer path for designing musical solid state Tesla coil which can increase their use in the entertainment industry.This design can be further improved to make it cost effective, consumes low power and works with lower input voltage.A desktop entertainment device can be designed with such improvements for consumer centric applications.In educational institutions these SSTCs can be used to demonstrate the resonance and modulation of high voltage arcs to produce music.In future research, output spectrum and correlation of music from output arcs with original music can be improved by utilizing various advanced audio modulation techniques.

FIGURE 2 .
FIGURE 2. The transformer of the solid state tesla coil (SSTC).

FIGURE 6 .
FIGURE 6. Clock signal generation circuit.here clock is referred to as the square wave whose fundamental frequency is the resonant frequency of the secondary coil.

FIGURE 12 .
FIGURE 12. LTspice circuit for drive signal generation with fixed interrupt.

FIGURE 15 .
FIGURE 15.Music-based interrupter using OPAMP and single supply.

FIGURE 16 .
FIGURE 16.Output at various stages of implemented music based interrupter.

FIGURE 18 .
FIGURE 18.Output at various stages of implemented feedback circuit.

FIGURE 19 .
FIGURE 19.Complete setup.different labels are used to indicate different sections of the circuit.

FIGURE 23 .
FIGURE 23.The measured clock signal from the 555 timer IC.

Figure 22
Figure 22 shows the feedback circuit.A simple wire was used as the antenna in the feedback circuit.It should be noted that the wire should be sufficiently close to the transformer tower to receive the radiated signals and work properly.
Authorized licensed use limited to the terms of the applicable license agreement with IEEE.Restrictions apply.

FIGURE 25 .
FIGURE 25.Produced arcs at 100Vdc from Full bridge rectifier and at 50% interrupt duty cycle.

FIGURE 26 .
FIGURE 26.Produced arcs at 100Vdc from Full bridge rectifier and at 20% interrupt duty cycle.

TABLE 1 .
Music A: Correlation between the original music and recorded output music.FIGURE 28.Music B: power spectrum analysis of original music (Top) vs. music recorded from tesla coil output (Bottom).

TABLE 2 .
Music B: Correlation between the original music and recorded output music.