Editing Tesla coil (section)

==Types==
The term "Tesla coil" is applied to a number of high-voltage resonant transformer circuits.

===Excitation===
Tesla coil circuits can be classified by the type of "excitation" they use, what type of circuit is used to apply current to the primary winding of the resonant transformer:<ref name=":0"/><ref name="oneTesla"/><ref name="Denicolai3"/>
* '''Spark-excited''' or '''Spark Gap Tesla Coil (SGTC)''': This type uses a [[spark gap]] to close the primary circuit, discharging a capacitor through the resonant transformer, exciting oscillations. Spark gaps have disadvantages due to the high primary currents they must handle. They produce a very loud noise while operating, noxious [[ozone]] gas, and high temperatures which may require a cooling system. The energy dissipated in the spark also reduces the [[Q factor]] and the output voltage. Tesla's coils were all spark-excited.
** '''Static spark gap''': This is the most common type, which was described in detail in the previous section. It is used in most entertainment coils. An AC voltage from a high-voltage supply transformer charges a capacitor, which discharges through the spark gap. The spark rate is not adjustable but is determined by the 50 or 60&nbsp;Hz line frequency. Multiple sparks may occur on each half-cycle, so the pulses of output voltage may not be equally-spaced.
** '''Static triggered spark gap''': Commercial and industrial circuits often apply a DC voltage from a power supply to charge the capacitor, and use high-voltage pulses generated by an oscillator applied to a triggering electrode to trigger the spark.<ref name="Haddad"/><ref name="Denicolai3"/> This allows control of the spark rate and exciting voltage. Commercial spark gaps are often enclosed in an insulating gas atmosphere such as [[sulfur hexafluoride]], reducing the length and thus the energy loss in the spark.
** '''Rotary spark gap''': These use a spark gap consisting of electrodes around the periphery of a wheel rotated at high speed by a motor, which create sparks when they pass by a stationary electrode.<ref name="Denicolai3"/> Tesla used this type on his big coils, and they are used today on large entertainment coils. The rapid separation speed of the electrodes quenches the spark quickly, allowing "first notch" quenching, making possible higher voltages. The wheel is usually driven by a [[synchronous motor]], so the sparks are synchronized with the AC line frequency, the spark occurring at the same point on the AC waveform on each cycle, so the primary pulses are repeatable.
* '''Switched''' or '''Solid State Tesla Coil (SSTC)''': These use [[power semiconductor device]]s, usually [[thyristor]]s or [[transistor]]s such as [[MOSFET]]s or [[IGBT]]s,<ref name="Haddad"/> triggered by a solid state [[electronic oscillator|oscillator]] circuit to switch pulses of voltage from a DC power supply through the primary winding.<ref name="Denicolai3"/> They provide pulsed excitation without the disadvantages of a spark gap: the loud noise, high temperatures, and poor efficiency. The voltage, frequency, and excitation waveform can be finely controllable. SSTCs are used in most commercial, industrial, and research applications<ref name="Haddad"/> as well as higher quality entertainment coils.
** '''Single resonant solid state Tesla coil (SRSSTC)''': In this circuit the primary does not have a resonant capacitor, only the secondary does; so it is a single [[tuned circuit]], not a double-tuned circuit. The current to the primary from the switching transistors excites resonance in the secondary tuned circuit. Single tuned SSTCs are simpler, but the single resonant circuit usually has a lower [[Q factor]] and so stores less energy and produces lower voltages than double resonant circuits, other things being equal.
** '''Dual Resonant Solid State Tesla Coil (DRSSTC)''': The circuit is similar to the double tuned spark excited circuit, except in place of the AC supply transformer (''T'') in the primary circuit a DC power supply charges the capacitor, and in place of the spark gap semiconductor switches complete the circuit between the capacitor and the primary coil.
[[File:StarWarsMainThemeOnTeslaCoil.webm|thumb|[[Star Wars (Main Title)|Star Wars theme]] performed on a tesla coil, [[Rankine Generating Station|Niagara Parks Power Station]], 2024]]
** '''[[Singing Tesla coil]]''' or '''musical Tesla coil''': This is not a separate type of excitation, but a modification to the solid state primary circuit to create a Tesla coil which can be played like a musical instrument, with its high-voltage discharges reproducing simple musical tones. The drive voltage pulses applied to the primary are modulated at an audio rate by a solid state "interrupter" circuit, causing the arc discharge from the high-voltage terminal to emit sounds. Only tones and simple chords have been produced so far; the coil cannot function as a [[loudspeaker]], reproducing complex music or voice sounds. The sound output is controlled by a keyboard or [[MIDI file]] applied to the circuit through a [[MIDI]] interface. Two [[modulation]] techniques have been used: AM ([[amplitude modulation]] of the exciting voltage) and PFM ([[pulse-frequency modulation]]). These are mainly built as novelties for entertainment.
* '''Continuous wave''': In these the transformer is driven by a [[Electronic oscillator|feedback oscillator]], which applies a pulse of current to the primary winding each cycle of the RF current, exciting a continuous oscillation.<ref name="Denicolai3"/> The primary tuned circuit serves as the [[tank circuit]] of the oscillator, and the circuit resembles a [[radio transmitter]]. Unlike the previous circuits which generate a pulsed output, they generate a continuous [[sine wave]] output. Power [[vacuum tube]]s are often used as active devices instead of transistors because they are more robust and tolerant of overloads. In general, continuous excitation produces lower output voltages from a given input power than pulsed excitation.<ref name="Denicolai3"/>

===Number of coils===
Tesla circuits can also be classified by how many resonant [[electromagnetic coil|coils]] ([[inductor]]s) they contain:<ref name="Gerekos4"/><ref name="Denicolai4"/>
* '''Two coil''' or '''double-resonant''' circuits: Virtually all present Tesla coils use the two coil [[resonant transformer]], consisting of a primary winding to which current pulses are applied, and a secondary winding that produces the high voltage, invented by Tesla in 1891. The term "Tesla coil" normally refers to these circuits.
* '''Three coil''', '''triple-resonant''', or '''magnifier''' circuits: These are circuits with three coils, based on Tesla's "magnifying transmitter" circuit which he began experimenting with sometime before 1898 and installed in his Colorado Springs lab 1899–1900, and patented in 1902.<ref name="Patent1119732"/><ref name="Sarkar2"/><ref name="Reed"/> They consist of a two coil air-core step-up transformer similar to the Tesla transformer, with the secondary connected to a third coil not magnetically coupled to the others, called the "extra" or "resonator" coil, which is series-fed and resonates with its own capacitance.  The output is taken from the free end of this coil.  The presence of three energy-storing [[tank circuit]]s gives this circuit more complicated resonant behavior.<ref name="de Queiroz"/> It is the subject of research, but has been used in few practical applications.