Mobile Phone Battery Charger

Small and portable unit, Can be assembled on veroboard

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

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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