Unfortunately, many of the circuits use an LM317 three-pin regulator IC. Now it’s not a bad IC but just a wee bit of overkill.
The LM7805 is very similar except that it’s designed to give you a 5V output at up to one amp. There are no divider or voltage setting resistors required. In fact, you don’t strictly need the two capacitors in this circuit above – they’re there just to clean up the supply a bit and ensure that it’s clean.
In Australia, you’ll pay around $2.75 for the LM317 but only $1.65 for the LM7805.
For standard USB devices, which require 5VDC anyway, the adjustability of the LM317 just isn’t needed. So you might as well save yourself a buck or more and go with the 7805 instead.
The 7805 can take an input voltage of up to 35V but the higher the input voltage, the more likely you’ll need a heatsink to keep the IC from blowing itself up with too much heat. (This is the same as the discrete 5V regulator circuit we looked at before).
Now while they’re not shown, you could add in either the single diode or the bridge rectifier to the front as polarity protection as shown in Circuit No. 2 and they’d do the same thing here.
Yep, this does smell awfully like a one-chip solution but we’ll take a look at a discrete voltage regulator in a little while.