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MOBILE CELLPHONE CHARGER

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A CHARGING CIRCUIT IS COMPOSED OF THE FOLLOWING STAGES OR SECTIONS:

1. Battery Charger Circuits - Although this is not found on mobile phones PC board circuit and have separate circuit but definitely this is also part of charging circuit; without this, the charging circuit is not complete and will not work completely.

This circuit is all parts and components that being mounted on any mobile phone charger, this is the one that converts AC (Alternating Current) voltage to DC (Direct Current) voltage.

What is AC Voltage? This voltage is a power source that we used in our household appliances to work and operate, this voltage can cause risk of electric shock and very dangerous to humans when being touch. This kind of voltage has an alternate polarity.

What is DC voltage? This voltage is a low level voltage which typically found on any kind of batteries.
These kinds of voltage have two polarities, the negative and the positive.

MOBILE CELLPHONE CHARGER

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Charging of the cellphone battery is
a big problem while travelling as
power supply source is not generally
accessible. If you keep your cellphone
switched on continuously, its battery will
go flat within five to six hours, making
the cellphone useless. A fully charged battery
becomes necessary especially when
your distance from the nearest relay station
increases. Here’s a simple charger that
replenishes the cellphone battery within
two to three hours.
Basically, the charger is a current-limited
voltage source. Generally, cellphone
battery packs require 3.6-6V DC and 180-
200mA current for charging. These usually
contain three NiCd cells, each having 1.2V
rating. Current of 100mA is sufficient for
charging the cellphone battery at a slow
rate. A 12V battery containing eight pen
MOBILE CELLPHONE CHARGER
D. MOHAN KUMAR cells gives sufficient
current (1.8A) to
charge the battery connected
across the output
terminals. The circuit
also monitors the
voltage level of the battery.
It automatically
cuts off the charging process when its output
terminal voltage increases above the
predetermined voltage level.
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 ZD1. Threshold pin 6 is supplied
with a voltage set by VR1 and trigger pin
2 is supplied with a voltage set by VR2.
When the discharged cellphone battery
is connected to the circuit, the voltage given
to trigger pin 2 of IC1 is below 1/3Vcc 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 the output goes low to
terminate the charging process. Threshold
pin 6 of IC1 is referenced at 2/3Vcc set by
VR1. Transistor T1 is used to enhance the
charging current. Value of R3 is critical in
providing the required current for charging.
With the given value of 39-ohm the charging
current is around 180 mA.
The circuit can be constructed on a
small general-purpose PCB. For calibration
of cut-off voltage level, use a variable DC
power source. Connect the output terminals
of the circuit to the variable power
supply set at 7V. Adjust VR1 in the middle
position and slowly adjust VR2 until LED1
goes off, indicating low output. LED1
should turn on when the voltage of the
variable power supply reduces below 5V.
Enclose the circuit in a small plastic case
and use suitable connector for connecting
to the cellphone battery.
Note. At EFY lab, the circuit was tested
with a Motorola make cellphone battery
rated at 3.6V, 320 mAH. In place of 5.6V
zener, a 3.3V zener diode was used. The
charging current measured was about 200
mA.The status of LED1 is shown in the table.