I think this is a buck converter, but I'm not entirely sure.

Hi Jake,

That is a voltage regulator, also known as a DC-DC converter or a Buck converter when it uses an inductor and switching and steps down the voltage.

You could confirm by examining the part code on the integrated circuit, and obtain the datasheet for the part online. It is extremely likely to be MC34063 (or similar) because that is common in low-cost USB car chargers (and from the photo, the pinout looks about right for that).

Thanks so much! I'm assuming the input voltage would be 12v, yes? Also, is there anyway i can change the output voltage? I'd like to lower it to around 4.7 volts.

Take a look at the datasheet for the controller here (assuming it is the one Shabaz is referring to): http://www.farnell.com/datasheets/1723944.pdf?_ga=1.226316314.1698039299.1446112257

If you look at Figure 15 on page 11 this is the circuit for a step down converter. In the circuit in this drawing R1 and R2 are the feedback resistors which are used to set the output voltage. The CII input feeds into a comparator inside the device, the other input being a 1.25V reference. The device will try and adjust the output such that the voltage on the CII input matches the reference voltage so if you want to change your output voltage then select values of R1 and R2 such that CII is at 1.25V for your desired output voltage.

Best Regards,

Rachael

ok so the big resistor up top is a 0.39 Ω ± 2%. I'm assuming thats the one that I need to replace, because there is no way I could replace the little ones on the bottom., and to figure out what I need to replace the top one with, i need to figure out the bottom resistors and plug them into that equasion thing. (cant seem to find it right now. anyone know it?)

ok so the big resistor up top is a 0.39 Ω ± 2%. I'm assuming thats the one that I need to replace, because there is no way I could replace the little ones on the bottom., and to figure out what I need to replace the top one with, i need to figure out the bottom resistors and plug them into that equasion thing. (cant seem to find it right now. anyone know it?)

Jake Linville wrote:

 

ok so the big resistor up top is a 0.39 Ω ± 2%. I'm assuming thats the one that I need to replace, because there is no way I could replace the little ones on the bottom.

Unfortunately that would be a bad assumption and the reason for the assumption is not good either

The 0.39 Ohm resistor is the current sense resistor for the active current limit. This equates to Rsc from Figure 15. So if you want to adjust the output voltage of this regulator you'll need to get yourself a decent soldering station and learn how to replace surface mount resistors yourself I'm afraid, unless you know anybody else than can do it for you.

Best Regards,

Rachael

ok so I've located r1. its 1.2Ω. Im still working on r2. once i find that, ill plug it into that equation that Texas instruments has, and I'll replace r1. and issues in doing that?

I hope it's not 1.2 ohm. Do you mean Kohm? You can do as you said to calculate the two resistor values. You might need to replace both to get the output you need as you will be restricted to standard values which can be easily obtained.

whoops. yea i meant  kohms. I found what I belive to be r1, its a .43 kohm and a 3.3 kohm in series, so if at all possible i want to try to only mess with r1.