What is Tesla Coil : Circuit Diagram, Working & Its Applications

The world of wireless technology is here! Innumerable wireless applications like wireless powered lighting, wireless smart homes, wireless chargers and so on are developed due to wireless technology. In 1891, the most famous discovery of the Tesla coil was invented by the inventor Nikola Tesla. Tesla was obsessed with providing wireless energy, which led to the invention of the Tesla coil. This coil does not require a complex circuit and so it is part of our daily lives like remote control, smartphones, computers, X-rays, neon and fluorescent lights, and so on.

What is Tesla Coil?

Definition: A Tesla coil is a radio frequency oscillator that drives the air-core double-tuned resonant transformer to produce high voltages with low currents.


To understand better, let’s define what is a radio frequency oscillator. Primarily, we are aware that the electronic oscillator is a device that produces electrical signals of either a sine wave or a square wave. This electronic oscillator produces signals in the radio frequency range of 20 kHz to 100 GHz, known as a radio frequency oscillator.

Tesla Coil Working Principle

This coil has the ability to produce output voltages up to several million volts based upon the size of the coil. The Tesla coil works on a principle to achieve a condition called resonance. Here, the primary coil emits huge amounts of current into the secondary coil to drive the secondary circuit with maximum energy. The fine-tuned circuit helps to shoot the current from primary to secondary circuit at a tuned resonant frequency.

Tesla Coil Circuit Diagram

This coil has two main parts – a primary coil and a secondary coil, with each coil having its own capacitor. A spark gap connects the coils and capacitors.The functionality of the spark gap is to generate the spark to excite the system.


Tesla Coil Working

This coil uses a specialized transformer called a resonant transformer, a radio-frequency transformer, or an oscillation transformer.


The primary coil is connected to the power source and the secondary coil of a transformer is coupled loosely to ensure that it resonates. The capacitor connected in parallel with the transformer circuit acts as a tuning circuit or an LC circuit to generate signals at a specific frequency.

The primary of the transformer, otherwise referred to as a resonant transformer steps up to generate very high levels of voltage ranging between 2kv to 30 kV, which in turn charges the capacitor. With the accumulation of massive amounts of charge in the capacitor, eventually, breaks down the air of the spark gap. The capacitor emits a huge amount of current through the Tesla Coil (L1, L2), which in turn generates a high voltage at the output.

Oscillation Frequency

The combination of a capacitor and primary winding ‘L1’ of the circuit forms a tuned circuit. This tuned circuit ensures that both primary and secondary circuits are finely tuned to resonate at the same frequency. The resonant frequencies of the primary ‘f1’ and secondary circuits ‘f2’ and are given by,

f1=1/2πL1C1 and f2=1/2πL2C2

As the secondary circuit cannot be adjusted, the moveable tap on ‘L1’ is used to tune the primary circuit till both the circuits resonate at the same frequency. Therefore, the frequency of the primary is the same as the secondary.

f = 1/2π√L1C1 =1/2πL2C2

The condition for primary and secondary to resonate at the same frequency is,

L1C1= L2C2

The output voltage in the resonant transformer does not depend on the number-of-turns ratio as in ordinary transformer. As soon as the cycle begins and as the spar sets up, the primary circuit’s energy is stored in the primary capacitor ‘C1’ and the voltage at which the spark breaks down is ‘V1’.


Similarly, the energy at the secondary coil is given by,


Assuming there is no loss of energy, W2 = W1. Simplifying the above equation, we get

V2 = V1√C1/C2 = V1√L2/L1

In the above equation, the peak voltage can be achieved when air breaks down do not occur. The peak voltage is the voltage at which the air breaks down and begins to conduct.

Advantages/Disadvantages of Tesla Coil

The advantages are

  • Allows uniform distribution of voltage throughout the winding coils.
  • Builds up the voltage at a slow pace and hence no damage.
  • Great performance.
  • The use of 3-phase rectifiers for higher powers can offer tremendous load sharing.

The disadvantages are

  • Tesla coil poses several health hazards due to high voltage radio frequency emission that includes skin burn, damage to the nervous system and heart.
  • Involves high costs in buying large DC smoothing capacitor.
  • Construction of circuit consumes much time as it needs to be perfect to resonate

Applications of Tesla Coil

At present, these coils do not require large complex circuits to produce high voltage. Nevertheless, small Tesla coils find their applications in a range of sectors.

  • Aluminum welding
  • Cars use these coils for the spark plug ignition
  • Created Tesla coil fans, used to generate artificial lighting, sounds like music Tesla coils in Entertainment and Education industry are used as attractions at electronics fairs and science museums
  • High vacuum systems and arc lighters
  • Vacuum system leak detectors


1). What do Tesla coils do?

This coil is a radio frequency oscillator that drives a resonant transformer to generate a high voltage at low current.

2). Can a Tesla coil charge a phone?

Nowadays, smartphones are released with built-in wireless charging, which uses the principle of a Tesla coil.

3). Is Tesla coil dangerous?

The coil and its equipment are very dangerous as they produce very high voltages and currents which cannot be ensured by the human body

4). Why do tesla coils make music?

Generally, this coil converts air around it into a plasma that changes volume and causes the waves to spread across all the directions, creating sound/music. This happens at a high frequency of 20 to 100 kHz.

5). How did Tesla transmit electricity wirelessly?

A spark gap is used to connect the capacitors and two coils. As the power is fed in through a transformer, it produces the necessary current and powers the entire circuit.

Thus, this is all about an overview of the Tesla coil that can be used to generate electricity of high voltage, low current, and high-frequency. Tesla Coil has the ability to transmit electricity wirelessly up to several kilometers. We ensured that this article gives the reader insights into the working of the Tesla coil, advantages and disadvantages, and applications. Truly, his invention of wireless transmission of electric energy has changed the way the world communicates.