Wireless Power Transfer with MOSFET

The metal-oxide-semiconductor field-effect transistor is fabricated with silicon-controlled oxidation most frequently. At present, this is the most commonly used transistor type because the main function of this transistor is to control conductivity, otherwise how much current can supply in between MOSFETs source & drain terminals depends on the sum of applied voltage to its gate terminal. The voltage applied to the gate terminal produces an electric field to control the conduction of the device. MOSFETs are used to make different application circuits like DC-DC converters, Motor control, Inverters, Wireless power transfer, etc. This article discusses how to design a wireless power transfer circuit using highly efficient MOSFET.

Wireless Power Transfer with MOSFET

The main concept of this is to design a WPT (wireless power transfer) system with MOSFETs and resonant inductive coupling for controlling the power transmission between a Tx & Rx coil. This can be done with resonant coil charging from AC, after that transmitting subsequent supply to the resistive load. This circuit is helpful in charging a low-power device very fast and powerfully through inductive coupling wirelessly.

Wireless power transmission can be defined as; the electrical energy transmission from the power source to an electric load for a distance without any cables or conducting wire is known as WPT (wireless power transmission). Wireless power transfer makes an extraordinary change within the electrical engineering field that removes the usage of conventional copper cables & also current-carrying wires. Wireless power transmission is efficient, reliable, low maintenance cost, and fast for long-range or short-range. This is used for charging a cell phone or rechargeable battery wirelessly.

Required Components

The wireless power transfer with a MOSFET circuit mainly includes the transmitter section and receiver section. The required components to make transmitter section for wireless power transfer mainly include; voltage source (Vdc) – 30V, capacitor-6.8 nF, RF chokes (L1 & L2) is 8.6 μH & 8.6 μH, Transmitter coil (L) – 0.674 μH, resistors R1-1K, R2-10 K, R3-94 ohm, R4-94 ohm, R5-10 K, Capacitor C works like a resonating capacitors, diodes D1-D4148, D2-D4148, MOSFET Q1-IRF540 and MOSFET Q2-IRF540

The required components to make a receiver section for wireless power transfer mainly include; diodes D1 to D4 – D4007, Resistor (R) – 1k ohm, voltage regulator IC – LM7805 IC, receiver coil (L) – 1.235μH, capacitors like C1 – 6.8nF and C2 is 220μF.

Wireless Power Transfer with MOSFET Connections

The connections of the wireless power transfer transmitter section follow as;

• The R1 resistor positive terminal is connected to a 30V voltage source and the other terminal is connected to LED. The cathode terminal of the LED is connected to GND through an R2 resistor.
• The R3 resistor positive terminal is connected to a 30V voltage source and another terminal is connected to the gate terminal of MOSFET. Here, the cathode terminal of the LED is connected to the gate terminal of MOSFET.
• The drain terminal of MOSFET is connected to the voltage supply through the positive terminal of the diode and inductor ‘L1’.
• The source terminal of MOSFET is connected to GND.
• In the inductor ‘L1’ another terminal is connected to the anode terminal of the D2 diode and its cathode terminal is connected to the R3 resistor through capacitors ‘C’ and inductor ‘L’.
• The R4 resistor positive terminal is connected to the voltage supply and the other terminal of the resistor is connected to the gate terminal of MOSFET through the anode and cathode terminals of diodes D1 & D2.
• The inductor ‘L2’ positive terminal is connected to the voltage supply and the other terminal is connected to the drain terminal of MOSFET through the anode terminal of diode ‘D2’.
• The source terminal of MOSFET is connected to GND.

The connections of the wireless power transfer receiver section follow as;

• The inductor ‘L’, capacitor ‘C1’ positive terminals are connected to the anode terminal of D1, and the other terminals of inductor ‘L’, capacitor ‘C1’ are connected to the cathode terminal of D4.
• The D2 diode anode terminal is connected to the D3 diode cathode terminal and the D3 diode anode terminal is connected to the D4 diode anode terminal.
• The D2 diode cathode terminal is connected to the D1 diode cathode terminal and the D1 diode anode terminal is connected to other terminals of inductor ‘L’, and capacitor ‘C1’.
• The resistor ‘R’ positive terminal is connected to the cathode terminals of D1& D2 and other terminals of a resistor are connected to an anode terminal of LED and the cathode terminal of LED is connected to GND.
• The capacitor C2 positive terminal is connected to an input terminal of LM7805 IC its other terminal is connected to GND and the LM7805 IC GND pin is connected to GND.

Working

This wireless power transfer circuit mainly includes two sections transmitter and receiver. In this section, the transmitter coil is made with 6mm enameled wire or magnet wire. Actually, this wire is a copper wire with a thin insulation coating layer on it. The diameter of the transmitter coil is 6.5 inches or 16.5cm & 8.5 cm in length.

The transmitter section circuit includes a DC power source, a transmitter coil & oscillator. A DC power source provides a stable DC voltage which is given as an input to the oscillator circuit. After that, it changes DC voltage into AC power with high frequency & is given to the transmitting coil. Because of AC current with high frequency, the transmitter coil will energize to produce an alternating magnetic field within the coil.

The receiver coil within the receiver section is made with 18 AWG copper wire which has an 8cm diameter. In the receiver section circuit, the receiver coil gets that energy as an induced alternating voltage in its coil. A rectifier in this receiver section changes the voltage from AC to DC. At last, this changed DC voltage is provided to the load throughout a voltage controller segment. The main function of a wireless power receiver is to charge a low-power battery through inductive coupling.

Whenever the power supply is provided to the transmitter circuit, then DC current supplies through the two sides of the L1 and L2 coils & to the MOSFETs drain terminals, then the voltage will appear at the gate terminals of MOSFETs & tries to switch ON the transistors.

If we assume that the first MOSFET Q1 is turned ON, then the drain voltage of the second MOSFET will be clamped to close to GND. Simultaneously, the second MOSFET will be in off condition, and the drain voltage of the second MOSFET will increase to peak & start to drop because of the tank circuit created by the ‘C’ capacitor & the oscillator’s primary coil throughout a single half cycle.

The advantages of wireless power transfer are; that it is less costly, more reliable, never runs out of battery power within wireless zones, it efficiently transmits more power as compared to wires, very convenient, eco-friendly, etc. The disadvantages of wireless power transfer are; that power loss is high, non-directionality, and not efficient for longer distances.

The applications of wireless power transfer involve industrial applications which include wireless sensors above rotary shafts, charging & powering of wireless equipment, and securing watertight equipment by removing charging cords. These are used for mobile devices charging, home appliances, unmanned aircraft & electric vehicles. These are used for operating & charging medical implants which include; pacemakers, subcutaneous drug supplies & other implants.  These wireless power transfer system can be created in home/breadbaord to understand its operation. let see

How to create a WirelessPowerTranfer device at home ?

Creating a simple wireless power transfer (WPT) device at home can be a fun and educational project, but it’s important to note that building an efficient WPT system with significant power output typically involves more advanced components and considerations. This guide outlines a basic DIY project for educational purposes using inductive coupling. Please be aware that the following is low-power and not suitable for charging devices.

Materials Needed:

• Transmitter Coil (TX Coil): A coil of wire (around 10-20 turns) wound around a cylindrical form, such as a PVC pipe.

• Receiver Coil (RX Coil): Similar to the TX Coil, but preferably with more turns for increased voltage output.

• LED (Light Emitting Diode): As a simple load to demonstrate power transfer.

• N-channel MOSFET (e.g., IRF540): To create an oscillator and switch the TX Coil.

• Diode (e.g., 1N4001): For rectifying the AC output from the RX Coil.

• Capacitor (e.g., 100μF): To smooth the rectified voltage.

• Resistor (e.g., 220Ω): To limit the LED current.

• Battery or DC Power Supply: To power the transmitter (TX).

• Breadboard and Jumper Wires: For building the circuit.

• Hot Glue Gun: To secure the coils in position.

Circuit Explanation:

          Let see how the Transmitter and receiver circuit has to be connected.

Transmitter Side (TX):

• Battery or DC Supply: This is your power source for the transmitter. Connect the positive terminal of the battery or DC power supply to the positive rail of your breadboard. Connect the negative terminal to the negative rail (GND).

• TX Coil (Transmitter Coil): Connect one end of the TX Coil to the drain (D) terminal of the MOSFET. The other end of the TX Coil connects to the positive rail of the breadboard, which is where the positive terminal of your power source is connected.

• MOSFET (IRF540): The source (S) terminal of the MOSFET is connected to the negative rail (GND) of the breadboard. This ties the MOSFET’s source terminal to the negative terminal of your power source.

• Gate (G) Terminal of the MOSFET: In the simplified circuit, this terminal is left unconnected, which effectively turns the MOSFET on continuously.

Receiver Side (RX):

• LED (Load): Connect the anode (longer lead) of the LED to the positive rail of the breadboard. Connect the cathode (shorter lead) of the LED to one end of the RX Coil.

• RX Coil (Receiver Coil): The other end of the RX Coil should be connected to the negative rail (GND) of the breadboard. This creates a closed circuit for the LED.

• Diode (1N4001): Place the diode between the cathode of the LED and the negative rail (GND) of the breadboard. The diode’s cathode should be connected to the cathode of the LED, and its anode should be connected to the negative rail.

• Capacitor (100μF): Connect one lead of the capacitor to the cathode of the diode (the anode side of the LED). Connect the other lead of the capacitor to the positive rail of the breadboard. This capacitor helps smooth out the rectified voltage, providing a more stable voltage to the LED.

That’s how the components are connected in the circuit. When you power the transmitter side (TX), the TX Coil generates a changing magnetic field, which induces a voltage in the RX Coil on the receiver side (RX). This induced voltage is rectified, smoothed, and used to power the LED, demonstrating wireless power transfer in a very basic form. Remember that this is a low-power and educational demonstration, not suitable for practical wireless charging applications.