Editing Tesla coil (section)

===Primary switching===
{{unreferenced section|date=August 2015}}
[[File:Maker Faire 2008 Tesla Coil.ogg|thumb|left|Demonstration of the Nevada Lightning Laboratory 1:12 scale prototype twin Tesla Coil at [[Maker Faire]] 2008]]

Modern [[transistor]] or [[vacuum tube]] Tesla coils do not use a primary spark gap. Instead, the transistor(s) or vacuum tube(s) provide the switching or amplifying function necessary to generate RF power for the primary circuit. Solid-state Tesla coils use the lowest primary operating voltage, typically between 155 and 800 volts, and drive the primary winding using either a single, [[rectifier|half-bridge]], or [[power electronics#Single-phase full-bridge inverter|full-bridge]] arrangement of [[bipolar junction transistor|transistors]], [[MOSFET]]s, or [[IGBT]]s to switch the primary current. Vacuum tube coils typically operate with plate voltages between 1500 and 6000 volts, while most spark gap coils operate with primary voltages of 6,000 to 25,000 volts. The primary winding of a traditional transistor Tesla coil is wound around only the bottom portion of the secondary coil. This configuration illustrates operation of the secondary as a pumped resonator. The primary 'induces' alternating voltage into the bottom-most portion of the secondary, providing regular 'pushes' (similar to providing properly timed pushes to a playground swing). Additional energy is transferred from the primary to the secondary inductance and top-load capacitance during each "push", and secondary output voltage builds (called 'ring-up'). An electronic [[feedback]] circuit is usually used to adaptively synchronize the primary [[oscillator]] to the growing resonance in the secondary, and this is the only tuning consideration beyond the initial choice of a reasonable top-load.

In a dual resonant solid-state Tesla coil (DRSSTC), the electronic switching of the solid-state Tesla coil is combined with the resonant primary circuit of a spark-gap Tesla coil. The resonant primary circuit is formed by connecting a capacitor in series with the primary winding of the coil, so that the combination forms a series [[LC circuit|tank circuit]] with a resonant frequency near that of the secondary circuit. Because of the additional resonant circuit, one manual and one adaptive tuning adjustment are necessary. Also, an [[interrupter]] is usually used to reduce the [[duty cycle]] of the switching bridge, to improve peak power capabilities; similarly, IGBTs are more popular in this application than [[bipolar junction transistor]]s or MOSFETs, due to their superior power handling characteristics. A current-limiting circuit is usually used to limit maximum primary tank current (which must be switched by the IGBTs) to a safe level. Performance of a DRSSTC can be comparable to a medium-power spark-gap Tesla coil, and efficiency (as measured by spark length versus input power) can be significantly greater than a spark-gap Tesla coil operating at the same input power.