If you search the internet looking for a ready made 5 volt regulator PCB you'll probably come across this device. At first glance it doesn't look anything special, but it's actually quite impressive. Conveniently for the voltage input there's a choice of either a two way terminal block or a standard 2.1mm DC socket. For the 5 volts output there's another two way terminal block or a type 'A' USB socket. Output current is dependant on the input voltage (see datasheet) but for an input voltage range of between 9V and 24V the output current is claimed to be 6A, though personally I would keep the current draw to 3A or less rather than work it to its limit. My only slight criticism would be that the printed circuit board could do with some mounting holes!

This project came about because I had an old 40 watt solar panel in my garden shed just sitting there doing nothing. Also in the shed was a nice little electronics enclosure begging to be put to good use. I was already using one of these regulator PCBs with the 12 volt solar power system that I already have, to charge my phone and other USB gadgets, and as they came as a pack of two I had a spare. So I thought why not throw all these parts together to make a self contained (sort of) solar powered gadget charger. OK so it's actually a 5 volt power supply rather than a charger, but then isn't that what all phone chargers are? So in this context I will stick to calling it a solar powered phone (or gadget) charger, as that is its intended purpose.

This board uses a buck regulator which is far more efficient than a linear regulator. There are other buck regulator boards out there which are much smaller and feature a simpler circuit design but those I have found get rather hot. This one does get a bit warm, but reassuringly not as much. The main regulating IC is a CX8571 that drives two output MOSFETS. The board also has another IC, the RZC7512 which is a dedicated charging port controller. This tells a connected phone whether it can fast charge or not, and also stops your phone having a moan at you because it thinks you're using an incompatible or faulty charging cable! Some boards use a CX2901A instead of an RZC7512 but their datasheets show that they are effectively the same IC. Although these are two channel devices, only one channel is used here (pins 3 & 4) as there is only one USB socket.

Something of high importance to me was that the regulator behaves itself if used with a solar panel. I didn't want it to produce any voltages below 5V if, for example, the sky was cloudy. I wanted it to be either completely 'ON' supplying 5 volts or completeley 'OFF'. I did not want a possible in-between state that might confuse any connected devices. A mobile phone will tolerate the occasional interupted charge, especially so if it's not actually going to be used, but I don't think it would appreciate something like 4 volts or less! This behaves perfectly though, producing 5 volts at the output when the input rises above 7.5V, returning to 0V when the input drops below 7.1V, with no undetermined state. Maybe that little bit of hysteresis helps in this respect.