Researchers predict that wireless power will make a significant contribution to energy supplies in the near future. The term “wireless power” describes the process of the transmission of energy from a power source to an electrical load, without connectors, across an air gap. The base of a wireless power system involves two coils — a transmitter and a receiver coil. The transmitter coil is energized by alternating current to generate a magnetic field, which, in turn, induces a current in the receiver coil. To achieve this, dc supplied by a power source is converted into high-frequency ac by supporting electronics built into the transmitter. The ac energizes a copper wire coil in the transmitter, which generates a magnetic field. Once a receiver coil is placed within proximity of the magnetic field, the field can induce ac in the receiving coil. Electronics in the receiver then convert the alternating current back to a usable ac/dc power. A lot of people have been asking me for a simple project on wireless power transfer, so here it is. However, this is not an efficient design, but good for almost all little demonstrations.
Now to the schematic of the demo module, which is an analog circuit that changes the dc into an HF square wave, shaping the power that can be coupled to another coil in close proximity. The prototype circuit was wired with parts I had lying around. The below pictures show the tested schematic, coil construction tip, and the prototype of the basic circuit. Admittedly, the basic circuit is an improvement of the well-known joule-thief (JT) concept and enables you to build your own demo module using widely available and inexpensive parts.
After completing and testing your own prototype, you can make a wireless LED bulb by enclosing the receiver circuit in a suitable LED bulb enclosure as shown below. Note that it’s also possible to rectify the output available across the receiver coil with the help of a bridge rectifier comprising four low-current Schottky diodes. Clearly, there is still a lot of work to be done before this circuit finds a veritable application!
Lab note: The maximum wireless power transfer range of the enwrapped-prototype is around 3 inches when tested with a fresh 1.5-V Duracell.