Power supply is a reference to the source of electrical power. Most electronic circuits require a DC power supply.
The most common operating voltages for microcontrollers and digital processors are 5V and 3.3V.
There are many different kinds of DC power supplies but this one is most commonly used here at ITP:
– Click on any image for a larger view
Most power supplies have a rating label that looks something like the one above. Make sure you know the polarity of the plug so you don’t reverse polarity for your circuit and damage your components. The diagram below showing positive tip polarity is on the left and negative tip polarity is on the right. The center positive drawing on the left indicates that the center (tip) of the output plug is positive (+) and the barrel of the output plug is negative (-).
V : Volts
A : Amperes
W : Watts
mA : miliAmperes
VA : Volt Amperes
VAC : Volts AC
VDC : Volts DC
DC : Direct Current
AC : Alternating Current
It is always good practice to test a power supply before using it for the first time. The example below will show how to test a power supply with positive polarity. If you have a negative polarity power supply, then you will get a negative reading. You should then switch the position of the multimeter probes.
If the voltage showing on your multimeter is more than half a volt or a volt off its rating, then you most likely have what is called an unregulated power supply. The 12V Jameco power supply we used in this example is a regulated one, so that is why the voltage we received was so close to the voltage it was rated for.