It is a long story though, still it's worth sharing. Once i had seen the minty boost instructable of ladyada, i was so impressed by it that i wanted to make one of them immediately. The concept of converting 3 volts to 5 volts with just a few components was just amazing, moreover in such a small size.
I left for Chandni Chowk (a place in Kolkata, India where you can get tonnes of electronic parts of all kinds) determined to buy a MAX 756 ic. But to my dismay, even after searching a few shops, i coudnt find it. I also tried to buy those linear-technology chips-LT 1073 and LT 1111, but still could not get it. I could not order it online too, beacuse it is costly and adding the shipping charges, it's just too much for a single chip. So my plans of making the minty boost shattered.
One day, an idea came to my mind. I thought to myself, why do i even need a costly chip, all i need to make is a charge pump, for which i needed a oscillating current source.
So i choose the very cheaply available NE 555 timer chip, made a schematic and tried my luck with it. Bingo! i recieved the same result. The project costed me less than 1$ or less than 60 INR. My joy knew no bounds ! I had made a variant of the minty boost with NE 555.
Step 1: Materials Required
I bought these from some random electronics hobby stores and have never bought any electronic components online.
1)NE 555 timer ic x1 ( any 555 will do).
2)Transistor- BC 547 x1
i) 0.01 uF(105) x2
i) 1N4148 x1
ii) 5.1 volt zener
5) Inductor - 100uH
6) USB port female
7)A DIP 8 Pin socket for NE 555
9) Soldering kit and some basic skills of soldering.
Step 2: Working Principle
I have provided a schematic, please note that the diode next to 1N4148 is a 5.1 v zener. I forgot to write, it. The transistor is BC 547, 2N222 will also do. The unmarked line is ground.
There is nothing to explain as such of the working principle. It is the same old concept of charge pump. Here the 555 timer ic provides a constant oscillating current source which feeds the oscillating current to the transistor. The inductor takes stage, boosts the current and dumps it back in the circuit. At last there is a rectification stage where the oscillating current is rectified back to get a dc output. The circut it simple but effective.
The current output is not so much, around 20mA. But its good for trickle charging.