9 3V Charger project

charger schematic and Inductor coil

This simple charger uses 2 AA or AAA 1.5v battery. It is easy to construct and electronic componenets are very cheap .This can be used to charge your cellphones, ipod or mp3 players.
The circuit is composed of simple oscillator, a rectifier, and voltage regulator. The feedback winding 1-2 is composed 5 turns of #24 AWG magnetic wire and main winding 2-3 is composed of 8 turns of #24 AWG wire (see diagram above).
Part List:
C1 - 470uF electrolytic capacitor rated 10V
R1 - 560 ohms 1/2W
Q1 - TIP41 NPN transistor or even 2N2222 will do
D1 - 1N4002 or any 1A rated diode
C2 - 220uF electrolytic capacitor rated 10V
DZ - 6.2V zener diode (1W)
R2 - 270 ohms resistor
LED - red, yellow and other low power LED
TIP41 pinout
2N2222 pinout
How to wind the Inductor:
Start winding in small toroid ferrite core (salvaged from old CFL) and mark it 1. Then continue until you reach 5 turns and mark it with 2. Continue winding with additional 8 turns and mark it 3. Follow the circuit above and your done. The winding are not critical,you can experiment using different number of turns.


  1. hey boss, how much current can this 3v charger can produce?

  2. Around 200mA to 400mA, depending how it is built. Decreasing the value of R1 increases the current.

  3. hi,
    I want to build a charger to charge IPOd's from a car 12v to approx. 5v 750mA. can u also publish a circuit on the above. thanks for the effort.

  4. The easiest way of converting your car voltage from 12V to 5V is using a 7805 regulator. Your 12V will be step down to 5V and can deliver up to 1500mA, more than enough of what you need. See the 12v to 5V for more info.
    If you need 5V supply with more than 5A current, I suggest see 12v to 5V (5A current) , you can also modify it to further increase its output current

  5. hi your projects are good, but where can i learn about the theory of this kind of converter.

  6. Based on my own understanding, basic electrical ideas:
    1. Voltage is generated or induced in a transformer when there is a change in current flowing in the coil (or flux in the core). Meaning constant current (DC) no induced voltage.
    2. Saturation of transistor. Usually, as the base current or voltage increases, the collector and emitter current increases. But there is a limit that any further increase in current or voltage in transistor base, collector or emitter current tends to be constant (approximate DC)
    3. Transformer core saturation. As you increase current to the coil, the flux in the core also increases, and as a result induced voltage to other coil increases. But there is saturation limit of the core that any further increase in current, the flux remains the same and there will be no voltage induced to the coil.
    How the circuit work:
    As you turn on the circuit, current flows to the coil and voltage is induced to the other coil. Since the voltage across the coil increases, the voltage across the base and collector of transistor increases and it will make the transistor turn on more. That will result to an increase in current flowing to the collector and the coil. Since the current flowing to the coil increases, the tendency is it will generate more voltage to the base of the transistor. Then the time will come that either the core or the transistor will saturate and will result to sudden drop in current. The voltage across the coils will reverse in polarity and forcing the transistor to turn off. That ends the first cycle and it s ready for the next cycle.

  7. can you guide me how to get the max current out of this circuit..
    How much should I decrease the value of R1 ?

  8. can you plz. show your solution on how the output voltage is become 5V from C1 to output., Thank you very much

  9. Why is there a 6.2v zener diode instead of a 5v, which matches the output?