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Automobile battery-based USB charger 


Electronic gadgets allocated almost every duty in our daily life, within a short period of time smartphones and other smart devices become popular.


Every single person using electronic devices facing a problem called charging, in our home automobile batteries for lead-acid batteries are very common, but we didn’t use it usefully we just throw it in scrap.

Today we made a charger from such an automobile High ampere batteries, the interesting part about this charger circuit is a wide range of its usage at any type of batteries.We can use this charger device for any type of batteries available at your market like AAA dry cell batteries to the heavy ampere car battery.


The making process of this battery charger circuit is been in a detailed step

1.    We made mini models circuit and try to detect advantages and disadvantages

2.    We  listed its advantages and disadvantages and try to make rectifications

3.    Made a profession circuit

Experimental circuit

Components used

 LM 7805 – IC

 1uf capacitors

 Connecting wires


Automobile battery-based USB charger using 7805
Automobile battery-based USB charger using 7805















The general way of rectification circuits will not be explained here, so after rectification an amount of DC voltage passing through circuit and entering into our regulator IC called LM7805, because a very easy way to step down the voltage is been provided by the IC. The regulator section only has three components and i.e. IC and two capacitors, the normal working process of this regulator is linear voltage regulation.

This mini circuit or experimental circuit’s detailed theoretical calculations and physical changes are been included in this post for a clear cut idea about its working and its development made.


After the construction of the circuit in a PCB board, and try to measure the voltage and current value, voltage measured at the input of an of the regulator is 6v, and the output we get is 5v, and the current mixture is 100mA.


So we concluded that our circuit is working properly, next we applied our output for charging the mobile phone, it is charging but our output current is only 100mA it is not enough for proper charging.


Next, we try to increase the input voltage of regulator circuit, it causes to increasing our charging speed but LM7805 become overheated, then we try to increase our output load consumption using high values of resistors and inductor load such as motors, but at a point, we realize that IC had a thermal overload protection system.


All these problems struck us is because of a voltage limit called the IC operation voltage limit starts at 7v.

 These are the output and input values for efficiency range detection

Pin = 12v * 0.33 ~ 4w

Pout = 5v * 0.33~ 1.7w

Efficiency = 1.7w/4w * 100% = 42.5%

These are the input and output values and the efficiency range for the circuit, efficiency theory states that higher the input voltage, we get low-efficiency value.


So, the increase of heat IC is due to this higher input value given into the regulator

Modified circuit

We mentioned earlier about the working of the regulator circuit, normally it works as a linear voltage regulator at circuits, but the experiment circuit proves us that linear regulation will not help us to attain high efficiency.


We need to change its working operation into alternating or shift mode, for modifications we need Schottky diode, inductor coil of 100uH 2.5 ampere, and some electrolytic capacitors.


Automobile battery-based USB charger using lm2576
Automobile battery-based USB charger using lm2576

Components used

Lm2576 IC

100uH inductor

Schottky diode

Capacitors 100uH and 1000uH


Circuit explanation

                          This is the new circuit very small changes are being made for the rectification.

LM7805 IC is replaced by LM2576 IC because 7805 gives us only 5v output, here 2576 provided 25v so we can use it for making adjustable power charging circuits.


Schottky diode

Shottky diode is a semiconductor component that is used to pass current in a single direction and block the second passage with infinite resistance.

Modifications made in this circuit are under the right way of analyzing and measuring strategies and also we can use this circuit professional-level also.

USB female socket

         Before starting our construction, we need a USB female socket new or old one.

If you collect the scrap one you need to follow these steps, as we desolder it from the old circuit board, first we need to check its proper working and also its ports connections.


As we consider about USB female socket with 4 painted,  2 pins at both two ends are 5v+ and GND, then the middle two pins are D+ and D-, here we need to short both data pins. 


 Working operation

After completing the connections, we connect 6v supply into the input of regulator and at the output we get 5v.


Here we use 6v supply to reach higher values of output (1v to 25v), earlier we mentioned about the operation voltage of IC started at 7v, we cross this limit, IC become overheated, but here we try to limit the voltage at 6 volts.


We get 600mA with 12v supply and it will take 300mA as input current.

Pin= 12v*0.3~ 3.6w

Pout=5v*0.6~ 3w

Efficiency=3w/3.6*100%~ 83%


Earlier problems appeared in the efficiency range but, here it is clear that efficiency becomes doubled in our modified circuit, 42% to 83%, it is because of the low voltage value.


This charger circuit can have the ability to charge your electronic gadgets using any kind of battery such as an automobile battery or a solar battery.


Normally, power supply circuits or charging circuits didn’t get a constant efficiency because of its variety of supply, but this circuit ensures a constant ability to maintain efficiency.

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