Much the use of USB devices today, sometimes cause lack of power problem. How to know the maximum current that can be obtained from a single USB connector is limited to 500 mA. If your device requires more current, then it must involve an additional one USB connector, which maybe not available. This problem can be solved by an additional instrument to use an external unregulated power and convert it to 5 Volt.
You can use two different approaches. You can use two different approaches. the first and perhaps easiest – is to use a simple linear regulator, but this raises other problems – wasteful spending power, but you can go the other way and use a pulse transformer, which is more economical.
Note : The basis of the converter is a PWM controller based on integrated circuits LM 2575-5, having the output of 5 volts with a current up to 1A. To enable / disable the converter uses pin 5 On / Off , controlled transistor VT 1.
