FRIENDLY CHARGER FOR MOBILE PHONES

[madhava543]

current/voltage regulation or short-circuit protection. These chargers provide raw 6-12V DC for charging the battery pack. Most of the mobile phone battery packs have a rating of 3.6V, 650 mAh. For increasing the life of the battery, slow charging at low current is advisable. Six to ten hours of charging at 150-200mA current is a suitable option. This will prevent heating up of the battery and extend its life. The circuit described here provides around 180mA current at 5.6V and protects the mobile phone from unexpected voltage fluctuations that develop on the mains line. So the charger can be left on over night to replenish the battery charge.

The circuit protects the mobile phone as well as the charger by immediately disconnecting the output when it senses a voltage surge or a short circuit in the battery pack or connector. It can be called a middle man between the existing charger and the mobile phone. It has features like voltage and current regulation, over-current protection, and high- and low-voltage cut-off. An added speciality of the circuit is that it incorporates a short delay of ten seconds to switch on when mains resumes following a power failure. This protects the mobile phone from instant voltage spikes.

The circuit is designed for use in conjunction with a 12V, 500mA adaptor (battery eliminator). Op-amp IC CA3130 is used as a voltage comparator. It is a BiMOS operational amplifier with MOSFET input and CMOS output. Inbuilt gate-protected p-channel MOSFETs are used in the input to provide very high input impedance. The output voltage can swing to either positive or negative (here, ground) side. The inverting input (pin 3) of IC1 is connected to 12V stabilised DC voltage developed across zener ZD1. This makes the output of IC1 high. After a power resumption, capacitor C1 provides delay of a few seconds to charge to a potential higher than of inverting pin 2 of CA3130, thus the output of IC1 goes high only after the delay.

In the case of a heavy power line surge, zener diode ZD1 (12V, 1W) will breakdown and short pin 3 of IC1 to ground and the output of IC1 drops to ground level. The output of IC1 is fed to the base of npn Darlington transistor BD677 (T2) for charging the battery. Transistor T2 conducts only when the output of IC1 is high. During conduction the emitter voltage of T2 is around 10V, which passes through R6 to restrict the charging current to around 180 mA. Zener diode ZD2 regulates the charging voltage to around 5.6V.

When a short-circuit occurs at the battery terminal, resistor R8 senses the over-current, allowing transistor T1 to conduct and light up LED1. Glowing of LED2 indicates the charging mode, while LED1 indicates shortcircuit or over-current status. The value of resistor R8 is important to get the desired current level to operate the cut-off. With the given value of R8 (3.3 ohms), it is 350 mA. Charging current can also be changed by increasing or decreasing the value of R7 using the I=V/R rule.

Construct the circuit on a common PCB and house in a small plastic case. Connect the circuit between the output lines of the charger and the input pins of the mobile phone with correct polarity

[viva]

This article is presented by:
T.K. HAREENDRAN

MOBILE PHONE BATTERY CHARGER

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. The 220-240V AC mains supply is downconverted to 9V AC by transformer X1. The transformer output is rectified by diodes D1 through D4 wired in bridge SANI THEO configuration 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. LED2 works as a power indicator with resistor R1 serving as the current limiter and LED3 indicates the charging status. During the charging period, about 3 volts drop occurs across resistor R2, which turns on LED3 through resistor R3. An external DC supply source (for instance, from a vehicle battery) can also be used to energise the charger, where resistor 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 LED1 connected between the common terminal (pin 2) and ground rail of IC1 raises the output voltage to 7.8V DC. LED1 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.

[ankitvj]

sir please help me as i need to submit a project on friendly mobile charger by next monday..so plz help me out with the proper diagrams and reports for the same..!!