USB battery charger
The charger works like a 500 mA iPhone charger and will work with most modern phones.
The main component in this circuit is the voltage regulator 7805 (U1). This is a component that takes an input voltage of 7V or above and gives out 5V. The diode (D1) placed in front of the input of the 7805 does two things: It makes sure you can't damage the circuit by connecting the plus and the minus of the battery the wrong way around. And it drops the voltage from the batteries 1v down, from 9V to 8V, which helps take some heat away from the voltage regulator. The Light-Emitting Diode (LED) is there to show you when the charger is working. The resistor R1 makes sure the LED doesn't have too much current flowing through it. The resistors (R2-R5) are there to tell your phone that this charger supports up to 500 mA (0.5 A) charging. If you don't know these components and their symbols, check out one of my most popular articles ever:
These are the components you'll need for this project:
Voltage regulator 7805
2 x Resistor 75 kΩ
2 x Resistor 51 kΩ
Resistor 330 Ω
Light-Emitting Diode (it indicates that there is power flowing out of the USB)
Rectifier Diode
USB socket
Stripboard Battery holder 6 x AA or just a battery of 6v
If you think the charging rate is too slow, you can increase the charging rate to 1A by replacing resistors R2 with a 43 k resistor. The problem with 1A is that Ω not all batteries are able to give 1A, and 1A will make the voltage regulator much hotter. But with a good heatsink, that shouldn't be a problem.
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