In this article we learn how to build a simple DC cell phone charger circuit using a single IC 7805 and some passive components.
A simple DC cell phone charger circuit is one of those mates of cell phone that cannot be ignored because a cell phone would be dead without a charger.
Normally a DC cell phone charger circuit come as an integral part of a cell phone package and we use it in conjunction with our AC mains supply.
But what happens if your cell phone gasps for power in the middle of a journey, probably when you are driving or biking away on a middle of a highway?
How it Functions
A very simple yet reasonably effective DC to DC cell phone charger circuit is discussed in this article, which can be easily built at home even by a layman.
Though the proposed charger circuit won't charge your cell phone at the rate equal to a normal AC to DC charger, nevertheless it will complete the function without fail and won't betray you for sure.
The proposed DC cellphone charger circuit can be understood with the following points:
We all know the general specs of a cell phone battery, it's around 3.7 volts and 800 mAH.
It means the cell phone would require at around 4.5 volts for initiating the charging process.
However a Li-Ion battery which is employed inside cell phones are pretty sensitive to bad voltages and may just blow off causing serious life and property issues.
Keeping this in mind the cell phone internal circuitry is specifically dimensioned very strictly.
The parameters just won't permit any voltage which may be even slightly out of the range of the battery specifications.
The use of the versatile IC 7805 in the circuit answers the above issue just perfectly, such that the charging voltage at its output becomes ideally suitable for charging the cell phone battery.
A high wattage resistor connected at the output of the IC makes sure that the current to the cell phone stays well within the specified range, though this might have not been a problem anyway, the cell phone would just refuse to charge if the resistor was not included.
Circuit Diagram of the DC cellphone charger
You can use this DC cellphone charger circuit for charging you cell phone during emergencies when there's no mains AC outlets, the circuit may be powered from any 12 volt lead acid battery or similar DC power source
R1 = 5 Ohm, 2 Watt,
C1, C2 = 10uF/ 25V,
D1 = 1N4007,
IC1 = 7805, mounted on a heatsink,
Battery, any 12 volt automobile battery
DC Cell phone Charger using a Single Transistor
The next design explains a DC cell phone charger using a single BJT is probably the simplest in its forms and may be built very cheaply and used for charging any standard cell phone from a DC 12 volts external source.
Simulation and Working
The circuit diagram illustrates a rather straightforward design incorporating very few components for implementing the proposed cell phone charging actions.
Here the main active part is an ordinary power transistor which has been configured with another active part, the zenet diode for forming a nice little DC to DC cell phone charger circuit.
The resistor is the only passive component other than the above couple of active parts which has been associated in the circuit.
So just three component is to be used and a full fledged cell phone charger circuit is ready within minutes.
The resistor acts as the biasing component for the transistor and also acts as the "starter" for the transistor.
The zener has been included to inhibit the transistor from conducting more than the specified voltage determined by the zener voltage.
Though, a cell phone ideally requires just 4 volts for initiating the charging process, here the zener voltage and subsequently the output voltage has been fixed at 9V, because the current releasing ability of this circuit is not very efficient and assumably the power should be dropping to the required 4v level once the cell phone is connected at the output.
However the current may be decreased or increased by suitably increasing or decreasing the value of the resistor respectively.
If the cell phone "refuses" to get charged, the resistor value nay be increased a bit or a different higher value may be tried for making the cell phone respond positively.
Kindly note that the circuit was designed by me based on assumptions only and the circuit has not been tested or confirmed practically.
Using 1-A Simple Step-Down Switching Voltage Regulator
If you are not satisfied with a linear regulator charger, then you can opt for this 1 A simple step-down switching voltage regulator based DC cell phone charger circuit which works with a switched buck converter principle which enables circuit to charge a cell phone with great efficiency.
How it Works
In one of my previous posts we learned about the versatile voltage regulator IC LM2575 from TEXAS INSTRUMENTS.
As can be seen, the diagram hardly utilizes any external components for making the circuit functional.
A couple of capacitors a schottky diode and an inductor of all that is needed to make this DC to DC cell phone charger circuit.
The output generates an accurate 5 volts which becomes very much suitable for charging a cell phone.
The input voltage has a wide range, right from 7V to 60V, any level ma be applied which results the required 5 volts at the output.
The inductor is introduced specifically for obtaining a pulsed output at around 52 kHz.
Half of the energy from the inductor is used back for charging the cell phone ensuring that the IC remains switched only for half the charging cycle period.
This keeps the IC cool and keeps it effectively in working even without using a heatsink.
This ensures power saving as well as efficient functioning of the entire unit for the intended application.
The input may be derived from any DC source like an automobile battery.
Courtesy and Original Circuit: ti.com/lit/ds/symlink/lm2575.pdf
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