Switch mode voltage regulator 34063A

I just discovered these handy voltage regulators while trying to get an LM317 circuit to work.  These regulators are switching type, which means they do not regulate by wasting the excess voltage in a resistive manner as do the LM317 regulators.  Rather, they turn on and off rapidly, and use an inductor to store and release energy for theoretical 100% efficient operation.

I was working on a circuit to power my Garmin Etrex Legend (Blue) GPS from my vehicle 12 volt power supply.  The Etrex requires 3 volts, so that means shedding the extra 9 volts somehow, actually more than that when the engine is running and the 14.5v alternator’s preset is enforcing.  My first thought was to really “shed” those extra volts with an LM317 circuit.  The LM317’s are simply transistors with  a voltage reference and regulator circuit built in, and the transistor just acts as a resistor to actively dump whatever extra voltage there is, into heat, of course requiring a heat sink.  This wastes power of course, and I was hoping to leave the GPS running all the time, summer, winter etc.  Blah.  When I felt how much heat really got dumped to the heatsink, I was concerned about how this could affect the battery of my vehicle.

I ended up scavenging an old cell phone charger, which in turn led to my discovery of the 34063A chip.  This circuit basically emulates the adjustability and function of the LM317 but in switch mode, that is, eliminating the voltage wasting nonsense with all its heat sinks.  I found that a pair of precision resistors were fixing the cell phone charger’s voltage at about 6 volts, and so  I removed the resistors and put in a trim pot to adjust the voltage to 3v.  It worked amazingly well.  I found that the current draw on the input side was only 40mA with the backlight off, and 60mA with it on.  Coolness!  So I can leave the GPS on all the time, with backlight on all the time!  60mA is not going to drain the car’s battery, and now I can effectively eliminate the use, misuse, reuse, and replacement of alkaline batteries in my car-mounted Etrex Legend.  When I get a moment I’ll upload schematics and photos.