Mobile phone chargers available in the
market are quite expensive. The circuit presented here comes as a
low-cost alternative to charge mobile telephones/battery packs with a
rating of 7.2 volts, such as Nokia 6110/6150.
Circuit diagram:
Mobile Phone Battery Charger Circuit Diagram
Parts
R1 = 1K
R2 = 47R
R3 = 10R
R4 = 47R
C1 = 1000uF-25V
D1 = LEDs any color
D2 = LEDs any color
D3 = LEDs any color
D4 = 1N4007
D5 = 1N4007
IC1 = LM7806
T1 = 9VAC Xformer 250mA
BR1 = Diode bridge 1A
Circuit Operation:
The 220-240V AC mains supply is
down-converted to 9V AC by transformer T1. The transformer output is
rectified by BR1 and the positive DC supply is directly connected to the
charger’s output contact, while the negative terminal is connected
through current limiting resistor R2. D2 works as a power indicator with
R1 serving as the current limiter and D3 indicates the charging status.
During the charging period, about 3 volts drop occurs across R2, which
turns on D3 through R3.
An external DC supply source (for
instance, from a vehicle battery) can also be used to energies the
charger, where R4, after polarity protection diode D5, limits the input
current to a safe value. The 3-terminal positive voltage regulator
LM7806 (IC1) provides a constant voltage output of 7.8V DC since D1
connected between the common terminal (pin 2) and ground rail of IC1
raises the output voltage to 7.8V DC. D1 also serves as a power
indicator for the external DC supply. After constructing the circuit on a
veroboard, enclose it in a suitable cabinet. A small heat sink is
recommended for IC1.
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