Hi everybody, I am using a 3.6V~9V 800mA Regulated IC Circuit Board from dealextreme and I want to hook them up to a 12 volt powersupply (car battery). Does anybody know what resistor I would need to do this?
You could either use a set of variable resistors in parrallel to make a voltage divider, albeit one that wastes a lot of your available power, or simply use a number of diodes in series in order to drop the voltage down to the levels you desire. Both of these solutions aren't very efficient, but they are quick and easy ( with the diode solution being the easiest ).
I won't go into the parallel resistor voltage divider ( they are simple and can be easily Googled ), but to make the diode voltage reducer, simply:
1) determine how much current your circuit needs to carry ( in this case ~800 ma )
2) Go to your favorite electronics parts retailer and select a diode with roughly double the maxiumum current carrying capacity than you need.
3) Look on the diode's operating specs printed on the back of its packaging and note the Forward Voltage Drop caused by the diode ( noted by the symbol Vf ). This is usually about .7 volts for most silicon diodes.
4) Now simply solder the diodes in series with all their bias'es pointing in the same direction ( they all must be pointing in a direction where current is able to flow from the fist diode through the last diode w/o being blocked by any diodes in the middle ).
5) Lastly, you can make taps at the joints between each doide in order to take advantage of the different voltages available at each diode-diode junction. Just be sure you don't try to run something from more than one tap at a time or those devices operating further down the string will either receive less current than expected or no current, depending on how much is being drawn upstream within the string of diodes. It's not like anything would likely get damaged, but it simply might not work as expected if devices towards the end of the string aren't getting the amount of current they need or expect to operate properly.
