I have a battery that's designed to power a MacBook Pro (it's not an internal battery, it's an external battery meant to act in place of a charger, so it's got all the monitoring electronics internally).
Now, I wish to use this battery to power an iPhone dock. This dock has internal batteries itself, but they run out fast (only 3.6V, 1.8Ah), whilst this MacBook battery can provide 60Wh - which would increase the duration of the playback by many times, and stop the voltage dropping etc.
The only issue is that the iPhone dock DC in wants a 12V, 2A supply, whilst the Macbook battery will supply between 14.5 and 18.5V (4.5A max). I don't wish to play with fire by putting in too high a voltage (there could be no damage, I might have to buy a new dock), so I was hoping to regulate the voltage of the MacBook battery so that it could safely power the iPod dock.
I've been reading 'A designer's guide to the L200C voltage regulator' and it seems to ideal for this purpose, but some aspects seem a bit strange. Can I get someone to answer the questions I have with this circuit? The ST datasheet is here.
Firstly, I'm not sure what the black rectangle at the bottom is. It seems like one plate of a capacitor, but that can't be right... Can that be explained?
Secondly, am I to attach the positive lead of the battery to the top left line and the negative lead to the bottom left line? Is it the same for the output? (top right for positive, bottom right for negative?
Finally, I'm not really sure what Vref means in all of the equations in the datasheet. The values for R1 and R2 given in the documentation for a 12V output are 1 kilo-Ohm for R1, and 3.3kW for R2 (I assume that's a typo, and they mean kilo-Ohm). Do these values seem reasonable, and should I have R2 as a potentiometer (If so, what sort of potentiometer?)
I'm sorry to sound really needy - I wish to get this working, and I also have barely any knowledge of electronics!