Mobile Cellphone Battery Charger

Charging of the mobile phone battery is a huge issue while traveling as power supply source is not usually available. In case you keep your mobile phone switched on continuously, its battery will go flat within to six hours, making the mobile phone useless. A fully charged battery becomes necessary when your distance from the nearest relay station increases. Here is a simple charger that replenishes the mobile phone battery within to hours. Fundamentally, the charger is a current-limited voltage source. Usually, mobile phone battery packs need three.6-6V DC & 180-200mA current for charging. These usually contain NiCd cells, each having one.2V rating. Current of 100mA is for charging the mobile phone battery at a slow rate. A 12V battery containing eight pen cells gives sufficient current (one.8A) to charge the battery connected across the output terminals.

Diagram  of cellphone charger

The circuit also monitors the voltage level of the battery. It automatically cuts off the charging system when its output terminal voltage increases above the predetermined voltage level. Timer IC NE555 is used to charge & monitor the voltage level in the battery. Control voltage pin five of IC1 is supplied with a reference voltage of five.6V by zen-er diode ZD1. Threshold pin 6 is supplied with a voltage set by VR1 & trigger pin two is supplied with a voltage set by VR2. When the discharged mobile phone battery is connected to the circuit, the voltage given to trigger pin two of IC1 is below 1/3Vcc & hence the flip-flop in the IC is switched on to take output pin three high.

When the battery is fully charged, the output terminal voltage increases the voltage at pin two of IC1 above the trigger point threshold. This switches off the flip-flop & the output goes low to terminate the charging method. 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 necessary current for charging. With the given value of 39-ohm the charging current is around 180 mA.

The circuit can be constructed on a tiny 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. Fine-tune VR1 in the middle position & slowly fine-tune VR2 until LED1 goes off, indicating low output. LED1 ought to turn on when the voltage of the variable power supply reduces below 5V. Enclose the circuit in a tiny plastic case & use suitable connector for connecting to the cell phone battery.

Mobile phon Circuits to Get Even smaller

Transceivers, appliances such as mobile phones that can send and receive messages, have become smaller and smaller over the last few years, but users are about to experience a new meaning in miniaturisation.
Research at The Hong Kong University of Science & Technology (HKUST) has successfully combined a unique system architecture and new circuit design techniques to reduce them in size like never before.

Principal Investigator Dr Howard Luong said the handset of a typical mobile phone today may contain between 150 and 300 separate electrical components.

Transceiver circuitry (left) and Dr Leung’s equivalent combining off-chip components

His research group proposed and demonstrated circuit techniques that make it possible to combine many of these components to a single chip and therefore to significantly reduce the size of circuitry (see example in graphic). A US patent has been granted for one of the circuit techniques.
The transformation applies to the CMOS (Complimentary Metal-Oxide Semiconductor) manufacturing process, which can produce integrated circuits and systems with the highest integration level at the lowest cost. Applying new techniques to the CMOS process, Dr Luong’s research enables many “off-chip” components to be combined to realize a system-on-chip. “But,” he said, “this integration created great challenges in circuit implementation.” Part of the research was to solve the problems by new circuit design techniques.
“The system architecture and circuitry go hand in hand, he added. “They must both work, or neither will be useful.”
The resulting design gives the highest component integration in the smallest chip area ever reported, said Dr Luong.
In his design, all off-chip components are fitted into a central chip measuring 36 mm with packaging, and 8mm without being packaged.
Dr Luong’s miniaturisation method means appliances will soon be made for even lower cost and lower power consumption in addition to being much smaller in size and lighter in weight.
“With the lowering of cost, size and power, many new and interesting applications will become possible and practical,” he said.
Low-power wireless transceivers, for example, could be integrated into implanted devices such as heart pacemakers to wirelessly transmit and receive information between patients and doctors or monitoring systems.
Wearable mobile phones as small as wrist watches at an affordable price could also become a reality.

Auther
Principal Investigator
Dr Howard Luong