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To Construct a Portable Mobile Charger

Published on Apr 02, 2024


Why going for a costly Power Bank to charge Mobile Phone? Just use a 9V battery and a few components to make a Portable Mobile charger. Its cost is just Rs.25 and if you use a Rechargeable 9V battery, it can be used up to three years. The Mobile phone battery is a high efficient long lasting Lithium Ion battery that has thousands of charge / discharge cycles. It requires 4 -6 volt DC for charging and the charging current can be between 200- 400 mA. We can drop the 9V from the battery to 6 volt using a Voltage regulator. That’s all. Make it and enjoy the satisfaction of a project building.


To construct a portable mobile charger which supplies 7.5v to charge Samsung Galaxy Note I


Mobile Charger:-

A device used to charge the battery of a phone. It converts the high voltage supply to a lower voltage so the phone could get charged.


The barrier to the flow of current is called resistance. The devices which provide resistance is called resistor.


It is a semiconductor device used to switch electronic signal into electric power. It is composed of semi conductor material with at least 3 terminals for conductance of external circuits.


Light emitting diode is two lead semi conductor light source. It resembles pn-junction diode, which emits light when activated.


It is a device containing one or more cells that convert chemical energy into mechanical energy.

Materials Required:

• PCB board

• Battery

• Transistor {7805 pnp-ic}


• Resistor {1.5 k approximately}

• Battery cap

• USB port

• Connecting wire

• Soldering iron

• Soldering wire

Circuit Diagram

mobile charger


1. IC 7805 is the Voltage regulator that gives 5.8 fixed output voltage. Even though it is 6V rated, around 0 .2 V drop occurs in its output. So we get 5.8 Volt for charging the Mobile battery. An LED can be included at the output to confirm the working on the charger. LED drops around 1.8V, so we get 4 Volt for charging. It is sufficient to charge the 3.6 or 3.7 V Mobile battery.

2. First identify the + and – pins of the USB socket. These will be at the ends. Remove the middle Data + and Data- pins. You can check the pins using a USB cable connected to a power source. Then mark + and – pins for easy connections.

3. Connect the Red wire of Battery Snap to the input pin ( First pin ) of IC 7805 and Black wire to the Ground pin ( Second pin ).Now connect the Output pin ( Third pin ) of 7805 to the + pin of USB socket. Connect the – pin of USB socket to the Ground pin of 7805.

4. Now solder 1K resistor to the Anode of LED and connect the free end of resistor to the + pin of USB socket and Cathode of LED to the – pin of USB socket.

5. Now the Portable Mobile charger is ready. Connect Mobile phone using USB cable. Phone will charge.

Portable Mobile charger


The current drop across each LED – resistor combination is 100mA. The output current needed is 700mA to 1A. Hence, we have to choose the battery to give a compensated current i.e. compensating all the losses in LED – resistor combinations. Considering the case of only two sub-circuits as shown,

Current = Output current needed + [(number of LED and resistor combinations)*100mA]

= 800mA + (3 x100mA)

= 800mA + 300mA

= 1100mA

= 1.1A

Hence, the current by the voltage source should be 1.1A.

In a similar way, depending upon the number of ports, and hence in turn the number of LED-resistor combinations, the battery can be selected.



In this design, all one has to do to get additional ports is to connect another sub-circuit shown in the circuit diagram, between Vcc and Ground in the similar fashion as shown with two sub-circuits. In this way as many as 5 or 6 ports can be connected if needed. Depending on the number of ports that can be added the hardware design must have slots and the battery must be varied. [a maximum of only 24 V, 900 mA is needed]

Cost Effective

The overall cost of this circuit is very less and cost of production would also be very less.

Small in Size

This circuit is very compact, can easily be made and is very small in size and less in weight.

Simple Design

The design is very simple and not at all complex to use.

Device Compatibility

Not only mobile phones, but any other devices such as LED lamps, or night lamps to aid in typing for keyboards without backlight, or USB vacuums to clean keyboards, or USB connectable fans or any other gadget that works with USB cable can be used here. As the USB female is connected, any of these devices will also work on this device.

Low Power Consumption

The power consumed is very low as compared to other charger circuits, as, DC power is used.

Flexible Charging of the Bank

Usually a specific charger is needed to charge the power bank. But, in this case, any charger adapter can be used to charge the battery. Be it any old unused charger available in our homes or, the phone charger adapter itself, any of these can be used, with a very little change in the hardware of the device.


The concept of being able to charge mobile phones on the go has been a pleasant help to almost everyone in the present times. Ever since the increasing abilities and the decreasing cost of smart phones, their utility has increased but their power consumption is high. The present day smart phones have a very large storage capacity and the parallelism with respect to apps associated with them is increasing rapidly. Running many applications at a time causes the phones to drain out quickly. Although increased charge consumption for a host of parallel and quick applications is a good bargain, this also calls for the phone being charged frequently. As power supply sockets are not available all the time, power banks come in handy.

This design will help in reducing overall cost of the device and also help people by relaxing the need of phone chargers and separate chargers for USB devices. It will definitely be helpful over the days, as, the speed and advancements in phones are at an exponential rate which decreases the charge of phones greatly. Hence, this calls for easier solutions to phone charging. This will also prove helpful to the newly emerging wearable electronic gadgets as, the size and power rating is ideal for that usage as well.