Download Wireless mobile battery charger

WIRELESS BATTERY CHARGER
GOMPO TASHI 10MSL0019
M.Sc ELECTRONICS
SCHOOL OF ADVANCE SCIENCE
GUIDE : PROFESSOR BOOPALAN (SENSE)
Introduction and motivation

Portable electronic devices are very popular nowadays.

As the usage of these portable electronic devices is increasing, the demands for
longer battery life are also increasing.

These batteries need to be recharged or replaced periodically.

So this project is to design a wireless battery charger.

We will use a concept called energy harvesting.
………

What if there was a way we could harvest the energy that is being transmitted and
use it as a source of power?

In the case of the cellular phone, this power could be used to recharge a battery
that is constantly being depleted.

The concept needs an efficient antenna along with a circuit capable of converting
alternating-current (AC) voltage to direct-current (DC) voltage.

The efficiency of an antenna, as being discussed here, is related to the shape and
impedance of the antenna and the impedance of the circuit.
Basic Principle….


The basic principle of an inductively coupled power transfer system.
It consist of a transmitter coil L1 and a receiver coil L2.
Primary coil
secondary coil
……..

Both coils form a system of magnetically coupled inductors.

An alternating current in the transmitter coil generates a magnetic field which
induces a voltage in the receiver coil.

This voltage can be used to power a mobile device or charge a battery.
Basic theory

Current and magnetic field
Ampere’s law states that current flowing in a conductor produces a magnetic field
around the conductor. The magnetic field produced by a current element
Bφ = μol/4πr( cosα2 – cosα1)
Bφ = μoI/2πr (Weber/m2)

Induced voltage in an antenna coil
Faraday’s law states that a time-varying magnetic field through a surface bounded by
a closed path induces a voltage around the loop.
V = - N dψ/dt

The negative sign shows that the induced voltage acts in such a way as to oppose
the magnetic flux producing it. This is known as Lenz’s law
Construction….

Inductive Coupling uses magnetic fields to transfer power.

Primary coil : it has z turns and generates a magnetic field.
it composed of a capacitor of 3.3nf in serial with coil .

Secondary coil : it has y turns and receives the magnetic field
it composed of a capacitor of 3nf in parallel with coil.

Transmitter : Here we are using function generator as a transmitter

Function generator needs to create 147.7 kHz square wave AC signal.
…..

Function generator power is fed to a series resonant network,

The current flowing through the coil in the network induces a sizeable
magnetic field around the transmitting “exciter” coil.
………..

A smaller coil of wire, with a capacitor wired in parallel, forms a parallel
resonant receiver circuit.

the smaller coil is placed in the centre of the larger coil, a sizable amount
of power can be coupled between them.

Diode bridge, or rectifier : It can turn AC into DC to power your portable
device.

The charge pump circuit is made of stages of voltage doublers.

This circuit is called a voltage doubler because in theory, the voltage that is
received on the output is twice that at the input.
Voltage doublers circuit
Voltage doublers waveform
The schematic represents one stage of the circuit.
Voltage doublers working

The RF wave is rectified by D2 and C2 in the positive half of the cycle and D1 and
C1 in the negative cycle

During the positive half-cycle, the voltage stored on C1 from the negative half-cycle
is transferred to C2.

The voltage on C2 is roughly two times the peak voltage of the RF source minus
the turn-on voltage of the diode.

By connecting these stages in series, we can essentially stack them, like stacking
batteries to get more voltage at the output.
Receiver

The receiver’s main purpose is to charge an X battery.

A simple battery charging theory is to run current through the battery, and apply a
voltage difference between the terminals of the battery to reverse the chemical
process.

At the output of the rectifier, the signal is not a fully DC signal yet.

By adding a capacitor and a resistor can smooth out the output to become DC
signal.

So doing that battery can charge wirelessly
Simulation

Multisim is a general purpose analog circuit simulator that is used to verify circuit
designs and to predict the circuit behaviour..

Voltage doubler simulation: by using three stages of doubler with same value of
capacitor and IN 4007 diode.
…..

Out put of above simulation:

Below peak to peak voltage is highest out put volt of voltage doublers.
…..

Voltage at output are gradually increasing with either increasing in no of stages and
values of capacitor.

At certain no of stages and capacitor values, the peak to peak volt is decreasing.
Input p to p
volt
capacitance
No of stages
o/p p to p volt
2
1uf
2
21
2
1uf
3
22.1
2
1uf
4
28.2
2
1uf to 15uf
4
19.5
2
15uf to 1uf
4
29.5
2
100uf to 40uf
4
25.5
2
1mf to 400uf
4
20.1
2
10mf to 4mf
4
11.2
Resonant frequency
Distance between two
coil (cm)
Resonant frequency
(KHz)
Peak to peak voltage
(volt)
0
116
39.2
0.5
115
35.8
1
113.5
33
3
112.5
24.4
6.5
111.7
9.6
10
112.4
4.25
11
113.2
3.53
12.5
113.3
2.91
Distance versus p to p voltage
….

Frequency versus voltage at constant distance between primary and secondary coil.

At 6cm
frequency (KHz)
Voltage(volt)
70
1.7
80
1.9
90
2.5
100
3.9
106
6.9
110
13.1
112
19.4
Frequency versus voltage
Design result

Primary coil :
Inductance = 520 uH
Resonant frequency = 117
Capacitance = 2.2nf
No of turns = 52
Gauge = 22
•
Secondary coil :
•
Inductance = 230 uH
Resonant frequency =16.9MHz
Capacitor = 823uf
No of turns = 72
Gauge = 18
Resonant frequency of over all circuit : 142.5KHz
•
Battery impedance is : 330ohms
•
….

Distances between primary and secondary coil : 5cm

Capacitor at load : 2200uF (35volt)

Voltage doublers diode : UF4007

Out put voltage : 3.6 volt

Out put current : 56.8mA

Out put watts : 204.48mW

By above result we can optimally charge the battery of cell phone.
THANK YOU