Skip to main content

Charger for mobile phones


Description
Most mobile chargers do not have 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 2) of IC1 is provided with a variable voltage obtained through the wiper of potmeter VR1. The non-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 Darlingtontransistor 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, whichpasses 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.
 author: Izhar Fareed - izhargmx.us  
 Source - extremecircuits.net

Labels:

Comments

Post a Comment

Popular posts from this blog

OP AMP INTEGRATOR CALCULATOR

Enter the Input Voltage,Vin: Volts Enter the Frequency, f: Hertz Enter the Input Resistance, Rin: Ohms Enter the Value of Capacitor, C: Farads Output Voltage, Vout: Volts OP AMP based Integrator Tutorial and Design
Post a Comment
Read more

Block diagram of AM transmitter and receiver with explanation

Block diagram of AM transmitter and receiver with explanation AM Transmitter : Transmitters that transmit AM signals are known as AM transmitters. These transmitters are used in medium wave (MW) and short wave (SW) frequency bands for AM broadcast. The MW band has frequencies between 550 KHz and 1650 KHz, and the SW band has frequencies ranging from 3 MHz to 30 MHz. The two types of AM transmitters that are used based on their transmitting powers are: ·          High Level ·          Low Level High level transmitters use high level modulation, and low level transmitters use low level modulation. The choice between the two modulation schemes depends on the transmitting power of the AM transmitter. In broadcast transmitters, where the transmitting power may be of the order of kilowatts, high level modulation is employed. In low power transmitters, where only a few watts of transmitting power are required , low...
Post a Comment
Read more

Using the TLP250 Isolated MOSFET Driver Explanation and Example Circuits

I’ve already shown how to drive an N-channel MOSFET (or even an IGBT) in both high-side and low-side configurations in a multitude of ways. I’ve also explained the principles of driving the MOSFETs in these configurations. The dedicated drivers I’ve shown so far are the TC427 and IR2110. Some people have requested me to write up on MOSFET drive using the very popular TLP250. And I’ll explain that here. The TLP250, like any driver, has an input stage, an output stage and a power supply connection. What’s special about the TLP250 is that the TLP250 is an optically isolated driver, meaning that the input and output are “optically isolated”. The isolation is optical – the input stage is an LED and the receiving output stage is light sensitive (think “photodetector”). Before delving any further, let’s look at the pin configuration and the truth table. Fig. 1 - TLP250 Pin Configuration Fig. 2 - TLP250 Truth Table Fig. 1 clearly shows the input LED side and the receiving photodetector as well...
Post a Comment
Read more