How do i make a usb charger using a l7805cv

[jpoopdog]

Hi,

I have a 12v to 5v step down converter, and i dont really trust it enough to wire it up directly to a usb hub to charge my phone (im charging from 12v portable battery source BTW), i was wondering am i fine to just use an L7805CV regulator to regulate the voltage? or is there something else i should do?
or do i even need the regulator at all would a capacitor and a resistor on the 5v be enough?
the step down converter can put out up to 5v 3A, and this phone, well, its my phone i dont wanna break it, any suggestions?
by the way, im not sure if its meant to be a function of the usb port or the phone to cut off/ block off power once the phone is full, but ill be keeping an eye on the power and once its full will disconnect the charger until its low, really this is just to extend the time i can use GPS functions on my phone which already has an annoyingly short capacity because of programs running in the background using cpu that i dont think i ever even installed or need, but i cant see them so i can get rid of them either, in any case, i need to go several hours on gps without a charger so making one is my only option.

 

[cowboybob]

Ordinarily, the device being charged (or powered) has the circuitry to control the current of the charging (or operating) process, irrespective of the charger's output current maximum (assuming that the charger's output voltage is stabile and correct).

So, the LM7805 would not be necessary and, more importantly, would not work correctly in a circuit such as you suggest: the LM78xx series require an input voltage greater than it's output level.

 

[audioguru]

If your phone can be charged by a USB port then its charger circuit is designed for an input of 5V. Using a higher voltage will probably cause the charger circuit to overheat and probably fail. So a 7805 regulator with the proper input and output capacitors, a 7.5V to 12V input and a suitable heatsink is perfect . Then a "step-down converter" is not needed.

 

[KeepItSimpleStupid]

Why don't you do it the right way. Use a USB charge controller: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CEwQFjAA&url=https://www.ti.com/lit/ds/symlink/tps2511.pdf&ei=PD5OUrCUHff_4AOJxIDICA&usg=AFQjCNEY7I7-uhtfJDiYb3Uwaa5MpLhZ2g&sig2=9CmbKt1Z7Ibbth_6fBFVgw&bvm=bv.53537100,d.dmg&cad=rja

This will support charging up to 2A as a dedicated port.

DON'T use a 7805 if the idea is to save battery life. I may have read your post wrong. Is the regulator your suggesting a switching regulator?

There are enough step-down DC-DC converters on ebay from China and elsewhere. Here is a fancy DC-DC step down.
**broken link removed**

Want to do it the easy way? Hardwire one of these: https://www.cyberguys.com/product-search/?keyword=usb charger car Done.