This source is designed according to the integrated this chip LM2577-12 is a DC-DC Step-Up, I mean a source that requires to deliver DC current but increasing its input voltage, in our case is set to enter the 5V from USB port and turn on 12V.
The circuit was extracted in part from the original datasheet, but have implemented some changes in my testing I performed better and added a power LED which is powered from the 12V output, this tells us that not only is 5V powered, but also becoming well-integrated tension. On the other hand we uh added a 1N4007 diode to 5V input polarity protection mode, such as integrated works from 2.5V forward, we can use instead of USB, two common batteries add 3V, for example to power a 5W LED with two batteries, of course consumption at 3V will be greater than 12V, the laws of thermodynamics apply to this circuit as the rest of the planet ...
To tell a little running start by describing the integrated package this in a TO220-5 (I added a sink but really in my test with a PC fan is not necessary for the low consumption of the fan), this integrated has 5 pins, the first of them is called Comp (this is responsible for connecting an RC oscillator which generates part of the oscillator frequency for the power switch), the second is called FEEDBACK (this this is the feedback pin is connected a high output voltage and its function is to take a sample of voltage and frequency for the integrated self-regulating and self stabilized in frequency), the third is GND (this pin will go to mass), the fourth is SWITCH (in this output shock or anger the high frequency transformer that generates the elevation of tension), and finally the fifth is Vin (this will be the input of the integrated fed.)
then the circuit fails, the PCB, photos and link to youtube .
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