I'm currently trying to build a USB charger device for my mobile phone using an old 12V car battery as power source. I purchased different step down modules (see below) to regulate the voltage from approx. 12V down to 5V.
My problem is, that as soon as I connect my mobile phone to the output of the step down regulator, the previously adjusted output voltage (via potentiometer) drops for about 0.7V causing the mobile phone to not charge properly. Example: I configured the step down module to provide 5.2V at the output. Without load, there is no problem. With my mobile phone attached the output of the step down regulator, the voltage drops to approx. 4.5V.
I checked the input voltage of the regulator from the battery. Without Load: 12.85V, with mobile phone connected: 12.74V.
Is the "unstable" input voltage responsible for the massive voltage drop on the step down output? Or is there anything I can do to improve output voltage stability under load? Because I don't want to set the regulator to 5.9V only that it will really deliver 5V when connected to my phone - I think that's not very comftable for the mobile phone?!
Do the regulators get hot?
Yes there are already decoupling caps on the board but these are insufficient for large loads. Their main use is to make the module stable but high impedances on input an output can disrupt that.
Assuming the regulators are not simply crap and give poor regulation then something is causing it and decoupling is always the first thing to try. The other thing is you could measure the regulation with a resistive load if you get some high wattage resistors.
The data sheet for the LM2596 recommends a 680 µF capacitor as the input decoupling they have used 220 µF so I would add say 470 µF across that.
This is typical of these cheap modules, anything to save a few cents. I bought a USB car charger some time ago. It worked on my Kindle and Lenovo tablet but my Samsung tablet gave a warning that the charger was faulty. On checking it had far too much ripple. Having opened it with a hacksaw I found wrong value capacitors were used. I chucked it and bought a better one.
I use another module to step down the voltage from 12v to 5v . The 5v is used to feed an Arduino and a two-channel relay module , when I connect the arduino and relay feeds to 5v , the step-down module's input voltage reduces to 9 volts(which should be 12v) and it's stable and gets hot. But I need the 12v to feed my electric valves.
I used MP1584EN DC-Dc 3A module and a 12v 2A adaptor. What am I doing wrong?
Grumpy_Mike:
How much current does your phone take. Poor regulation like you have is normally caused by asking the regulator for too much current.