03-11-2012, 01:53 PM
FRIENDLY CHARGER FOR MOBILE PHONES
FRIENDLY CHARGER.doc (Size: 763 KB / Downloads: 26)
Most mobile chargers do not have current/voltage regu- lation or short-circuit pro- tection. These chargers provide raw 6-12V DC for charging the battery pack. Most of the mobile phone bat- tery 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 op- tion. 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 unex- pected voltage fluctuations that de- velop 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 im- mediately 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 speci- ality of the circuit is that it incorpo- rates a short delay of ten seconds to switch on when mains resumes fol- lowing a power failure. This protects the mobile phone from instant voltage spikes. The circuit is designed for use in conjunction with a 12V, 500mA adap- tor (battery eliminator). Op-amp IC CA3130 is used as a voltage compara- tor. It is a BiMOS operational amplifier with MOSFET input and CMOS out- put. Inbuilt gate-protected p-channel MOSFETs are used in the input to pro- vide very high input impedance. The output voltage can swing to either posi- tive or negative (here, ground) side. The inverting input (pin 2) of IC1 is provided with a variable voltage ob- tained 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.
FRIENDLY CHARGER.doc (Size: 763 KB / Downloads: 26)
Most mobile chargers do not have current/voltage regu- lation or short-circuit pro- tection. These chargers provide raw 6-12V DC for charging the battery pack. Most of the mobile phone bat- tery 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 op- tion. 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 unex- pected voltage fluctuations that de- velop 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 im- mediately 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 speci- ality of the circuit is that it incorpo- rates a short delay of ten seconds to switch on when mains resumes fol- lowing a power failure. This protects the mobile phone from instant voltage spikes. The circuit is designed for use in conjunction with a 12V, 500mA adap- tor (battery eliminator). Op-amp IC CA3130 is used as a voltage compara- tor. It is a BiMOS operational amplifier with MOSFET input and CMOS out- put. Inbuilt gate-protected p-channel MOSFETs are used in the input to pro- vide very high input impedance. The output voltage can swing to either posi- tive or negative (here, ground) side. The inverting input (pin 2) of IC1 is provided with a variable voltage ob- tained 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.