Wireless Power Transfer Circuit: The Basic Concept

What is a Wireless Power Transfer Circuit? 

A wireless power transmission/wireless energy transfer refers to electrical energy transmission from a power source to an electrical load or receiver device without using the connecting wires or physical link. Not only is it fast and reliable, but you can also use it for short- or long-range transmissions. 

The wireless power transfer technology is recommendable for charging appliances like wireless devices, e.g., laptops, since it has galvanic isolation. Thus, there is a lower risk of having electrical shock. 

Working principle 

The wireless power transfer systems comprise a transmitter, medium, and receiver working under an inductive coupling power transmission principle. 

(wireless power transfer system)

Source: https://en.wikipedia.org/wiki/

Transmitter: Majorly, we apply electrical energy (in the form of electromagnetic energy in waves, light, or changing magnetic field). Then, the transmitter transmits the electrical energy to another form of energy, resulting in a suitable electrical power level.

Medium: Secondly, we have the medium that allows the passage of the transmitted energy. It can be either in a vacuum, air, or solid form. Please do not use a metallic medium because it won’t allow the passage of electrical energy for heat generation. 

Receiver: Finally, the receiver will receive the transmitted power and then convert it to electricity. And now, your wireless power device is ready for use. 

A wireless power transfer circuit 

The required components 

• 20-30 electromagnetic line (copper wire)

You can form the electromagnetic coil (with copper wires) by winding a conductor around a core. Often, it functions by using magnetic coupling for the transfer of energy within electrical circuits. Moreover, you can find several electrical coils, such as Maxwell coil, Tesla, Choke, and Barker, that match the recommended circuit parameters. 

• A battery -1.5V
• Transistor (2N2222)
• LED
• Resistors – 1.2k
• Breadboards 

Here are a few tips on designing the wireless power transmission circuit;

First and foremost, when dealing with the transmitter, you should have a 17-turns winding of wire, a loop for the center tap connection then another 17 turns of coiling wire. On the contrary, the receiver should only have 34 coil winding turns but no center tap connection. 

The structure of the circuit 

The simple circuit below has two parts: a receiver and a transmitter. 

Transmitter circuit and working

A transmitter-circuit 

An AC source is the power supply that drives the transmitter coil to create an electromagnetic field around it. Later, when the copper coil gets center-tapped, both sides will begin to have some charge. From the diagram, you can see that one side of the copper coil has a connection to the collector terminal of the NPN transistor while the other links with the resistor. 

When the system is charging, the base resistor will begin to conduct and then power up the transistor. Subsequently, the transistor discharges the inductor during the emitter’s connection to the ground. 

The simultaneous charging and discharging generate a high-frequency AC/ oscillation signal, leading to a magnetic field transmission. 

The receiver circuit and working 

A receiver-circuit 

The receiver coil examines the high-frequency magnetic field from the transmitter. Afterward, it begins generating EMF voltage that eventually lights up the LED light bulb. Faraday’s law of induction governs the operation of the receiver coil.

Wireless Power Transfer Circuit—The efficiency of Wireless Power Transmission

When it comes to efficiency, a WPT has an estimation of 10% or less efficiency. The formula for calculating the efficiency is;

Efficiency = (Output power / Input power) x 100%

Power = Volt x Current 

The huge efficiency loss explains why it is easy to apply wireless power transmission circuits in low-power applications, such as an electric toothbrush, and not in high-power machines, like electric cars. Furthermore, wireless-powered technological devices are not eco-friendly if a large audience is constantly using them. You will need to apply up to 10 times the power to start up the electrical device. Consequently, electrical energy production will increase and then become hazardous to the planet and the human body. 

Luckily, all types of wireless power transmission have regulations that favor human beings’ usage. 

Advantages and Disadvantages of the Wireless Power Transmission Circuit 

Advantages 

The merits of a wireless power transfer are;

• First, it is cost-effective.
• Then, you can easily design the circuit since it is a simple process.
• Also, its operating frequency current is low.
• Moreover, the WPT allows you to make a waterproof product since you’ll not need a power port to charge your device. 
• Again, you can increase your product’s longevity with a WPT. It is because you’ll be avoiding any direct physical damage to the products via charger insertion in ports or connectors. 
• Finally, its circuit design suits short distances (near-field communication).

Shortcomings 

As with any technological concept, the WPT also has demerits. They include;

• Unfortunately, it is inefficient for longer distances. However, to eliminate the distance challenge, you can increase the number of coil turns. 
• It also has low efficiency that you can solve by using better wireless transmission driver Integrated Circuits. Alternatively, you can use MOSFETs or transistors to construct push-pull topologies. 
• Additionally, you will experience high power/energy loss, which isn’t safe for the environment.
• Lastly, its features are of non-directionality/ nonlinear parity-time. 

Application of Wireless Power Transmission Circuit 

The wireless energy transmission circuit has a wide range of applications. They include the following;

• Model engineering,
• In the transport industry, for example, in electric vehicles,
• Industrial engineering,
• Medical devices/ biomedical implants,
• Retinal prosthetic applications, 
• Consumer electronics,
• Heating and ventilation sector. 

(wireless inductive charging of a mobile phone).

Conclusion 

To conclude, today’s post focuses on the basics of a wireless power transfer alongside a couple of its challenges, applications, and benefits. You can use the WPT in various technological systems, such as charging electric vehicles, portable devices, and mobile devices like cell phones. 

What’s more, achieving an efficient and robust wireless power transmission is possible because of the power-efficient switch-mode amplifier. The amplifier has current-sensing feedback in a powerful parity-time symmetry. Therefore, it helps in solving the non-directionality. 

In need of any technical help concerning WPT? Contact us, and we will get back to you as soon as possible.