9/4/2013

MOBILE PHONE BATTERY CHARGER

SUBMITTED BY:

Nupur Sahu- 111EC0188

Jagruti Patel- 111EC0182

Vishal Mishra- 111EC0179

ELECTRONICS DESIGN LABORATORY

PROJECT REPORT

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CONTENTS

Experiment no 1 .................................................................................................... 2

Objective................................................................................................................ 2

Introduction ........................................................................................................... 2

Theory ................................................................................................................... 2

SYSTEM DESIGN ..................................................................................................... 4

SIMULATION RESULTS ............................................................................................ 5

IMPLEMENTATION ................................................................................................. 6

RESULTS AND DISCUSSION ..................................................................................... 8

References ............................................................................................................. 8

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Experiment no: 1 Date: 04.09.2013

Title: MOBILE PHONE BATTERY CHARGER

Objective:

To design a mobile charger using pen cells, sufficient to charge a mobile battery,

which can be used while travelling. The charger provides sufficient performance

at low cost and is of small size and can be carried easily.

Introduction:

Cellphone battery is a big problem while travelling as power supply source is not

generally accessible. If we keep our cellphone switched on,the battery lasts for

only 5-6 hrs, making the cellphone useless.

The first charger uses four pen cells connected serially,it forms a battery pack

with 6V and 1.5Amps current. The transistor and resistor voltage combination

gives the rated voltage and current required to charge the battery.

The second charger charges the cellphone at a slow rate. A 12V battery containing

8 pen cells gives sufficient current(1.8amps) to charge the battery output

terminals. It automatically cuts off the charging process when its output voltage

reaches the pre-determined voltage level.

It is necessary to know when the battery has reached the fully charged

condition,or else the battery will be damaged in the long run. The charger

monitors the bettery’s state and stops charging when voltage of battery reaches

7V.

Theory:

1. INPUTS OF NE555 TIMER:

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TRIGGER INPUT:

When <(Vcc/3),i.e. active low,it makes output high. It monitors the

discharging of the timer capacitor in an astable circuit. It has high input

impedance.

THRESHOLD INPUT:

When >(Vcc/3),i.e. active high,it makes the output low(0V). It monitors the

charging of the timing capacitor in astable and monostable circuits. It has

high input impedance.

RESET INPUT:

When <(0.7V),i.e. active low,this makes the output low(0V),over-riding

inputs. When not required,it is connected to Vcc.

CONTROL INPUT:

This is used to adjust the threshold voltage which is set internally to be

(2/3Vcc). Usually this function is not required and the control input is

connected to 0V with a 0.01uF capacitor to eliminate electrical noise. It can

be left unconnected if noise is not a problem.

2. TRANSISTORS:

The BJTs used in the circuit is used so that rated current can be achieved

without significant voltage drop. The transistors used in the two circuits are

CL100 (NPN), BC548 (NPN) and BC558 (PNP).

3. ZENER DIODE:

The fact that the voltage across the diode in the breakdown region is

almost constant turns out to be an important application of Zener diode as

voltage regulator.

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SYSTEM DESIGN:

CIRCUIT 1:

Here is an ideal mobile charger using 1.5 volt pen cells to charge mobile phone

while traveling. It can replenish cell phone battery three or four times in places

where AC power is not available.

Most of the Mobile phone batteries are rated at 3.6 V/500 mA. A single pen torch cell can provide 1.5 volts and 1.5 Amps current. So if four pen cells are connected serially, it will form a battery pack with 6 volt and 1.5 Amps current. When power is applied to the circuit through S1, transistor T1 conducts and Green LED lights.

When T1 conducts T2 also conducts since its base becomes negative. Charging current flows from the collector of T1. To reduce the charging voltage to 4.7 volts, Zener diode ZD is used. The output gives 20 mA current for slow charging. If more current is required for fast charging, reduce the value of R4 to 47 ohms so that 80 mA current will be available. Points A and B are used to connect the charger with the mobile phone. Use suitable pins for this and connect with correct polarity.

CIRCUIT 2:

Timer IC NE555 is used to charge and monitor the voltage level in the battery.

Control voltage pin 5 of IC1 is provided with a reference voltage of 5.6V by Zener

diode D1. Threshold pin 6 is supplied with a voltage set by P1 and trigger pin 2 is

supplied with voltage set by P2. When the discharged cellphone battery is

connected to the circuit, the voltage given to trigger pins of IC1 is below Vcc/3

and hence,the flip-flop in the IC is switched on to take output pin 3 high. When

the battery is fully charged, the output terminal voltage increases the voltage at

pin 2 of IC1 above the trigger point threshold.

This switches off the flip-flop and output goes low to terminate the charging

process. Threshold pin 6 of IC1 is referenced at 2/3Vcc set by P1. Transistor Q1 is

used to enhance the charging current. Value of R3 is critical in providing the

required current for charging. With the given value of 39ohm,the charging current

is around 180mA. For calibration of cutoff voltage level,we use a variable DC

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power source. We connect the output terminals of the circuit to variable power

supply set at 7V. Adjust P1 in the middle position and slowly adjust P2 until

LED(D2) goes off,indicating low output.

LED should turn on when the voltage of the variable power supply reduces below

5V.

SIMULATION RESULTS

CIRCUIT 1:

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CIRCUIT 2:

IMPLEMENTATION:

The circuits were successfully implemented on a veroboard. A suitable mobile

connector for a Nokia phone was connected and the charger was tested on Nokia

2700. The battery specifications of Nokia 2700 are: Li-ion 1020 mAh battery (BL-

5C) which was within the current limits of the circuits implemented.

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RESULTS AND DISCUSSION:

The battery was successfully charged using the first circuit. It took about four

hours to reach the condition of full charge implying slow charging.

The second circuit could not be implemented due to voltage fluctuations in the

output terminals which could have been harmful for the battery.

While charging using first battery charger, the charger was removed after full

charge as it is not an automatic charger and could have damaged the battery by

charging further.

Thus the two battery charger circuits-one automatic and one manual were

realized on the veroboard with the manual charger working properly.

References

[1] Electroschematics, "http://www.electroschematics.com," [Online].

[2] "http://www.electronicsforyou.com," [Online].

[3] Wikipedia, "www.wikipedia.org," [Online].