What is that one thing that has to get in your way to help you charge your phone? The wires. These wires sometimes make it inconvenient to carry your phone while on charging. But now with a small amount of modification a portable wireless charger can be constructed thus making your life hassle-free. Wireless charging is also referred to as inductive charging because it employs the use of magnetic field to transfer energy. This transfer is usually from a charging station, henceforth referred to as a supply, to a rechargeable and moveable device.
The basic phenomenon behind the wireless charging is induction. An inductive charger uses a coil to form an alternating magnetic field in the primary winding which induces a field in the secondary coil (which is inside your cell phone) through the process of mutual induction once these two coils are placed close to each other. Hence, power is transferred from supply to mobile device via magnetic induction. The whole system can be divided into following subsystem we will discuss them all.
1. Power bank: Power bank is simply a DC source. It can either be your Car’s Battery or any other DC Source. Here we have used 12V DC supply.
2. The colpitts oscillator: The Colpitts oscillator is used here to generate the Sinusoidal Current from applied DC. Its circuit consists of a single stage inverting amplifier and an L-C phase shift network
When we apply a 12V collector supply voltage, the capacitors C3 and C4 are charged. These capacitors C3 and C4 discharge through the coil L, setting up oscillations of frequency given as:
f = 1 / 2∏√[1/LC3 + 1/LC4]
The oscillations developed across capacitor C4 are then applied as feedback to the base-emitter junction and it appears in the amplified form in the collector circuit. This amplified output is then supplied to the tank circuit In order to meet the losses and it will give sustained oscillations. The wave form is as shown below:
2. Amplifier: Here we have used push pull amplifier because of its ability towork in limited power supply. A push pull amplifier has an output stage that can drive a current in either direction through the load. The output stage of a push-pull amplifier comprises of two identical BJTs of which one sources current through the load while the other one sinks the current from the load. The whole arrangement is shown in figure below: ( Click on the image to load the circuit )
The output of oscillator stage is fed to the push pull amplifier and is split into two identical signals with phase difference of 180 degrees using the center-tapped transformer as shown in figure below
These signals are then applied to the two identical BJTs whose emitter terminals are connected. Thus amplified signal is then transferred to the receiving side by the use of current carrying wire loop of transformer. The output of this stage is shown in the figure below:
3. Receiver: The receiver consists of a half wave rectifier, RC filter and a constant voltage regulator PVR100AZ_B5V0 IC that will provide a constant Output voltage of 5 volts.
The first stage that is a half wave rectifier rectifies the received wave form which will then pass through the RC network that will act as a filter and will remove the ripples
Now the output of RC filter is fed to the constant output voltage IC that will provide a constant output voltage of 5 volts and several hundred milli-amperes which will be sufficient to charge your cell phone, music players, tablets etc. The final out waveform is shown below.
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