Direct current (DC) power supplies have several important components, including a transformer, rectifier, filter and voltage regulator. The transformer changes the voltage from the 110-volt household standard to a lower value and the rectifier and filter convert alternating current (AC) to DC and remove electrical noise. The regulator holds the output voltage steady despite varying circuit loads. Three-terminal devices, such as the 7805, regulate voltage levels to within a few percents. The 7805 designation indicates that it has a 5 volt output. The device contains most of the regulation circuitry; it needs only a couple external capacitors to make it work.
- Skill level:
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Things you need
- LM7805 voltage regulator
- Solderless breadboard
- .33-microfarad, 100-volt Mylar capacitor
- .1-microfarad, 100-volt Mylar capacitor
- 22-gauge solid, insulated wire
- Wire strippers
- Unregulated DC power supply, 7 to 12 volts
Insert the 7805 voltage regulator into the breadboard so its three pins go into separate vertical columns on the board.
Set one of the .33-microfarad capacitor's leads so it connects to the 7805's ground pin. Connect its other lead to the regulator's input pin. Connect one lead of the .1-microfarad to the 7805's ground pin. Insert its other lead so it connects to the 7805's output pin.
Cut four pieces of wire 12-inches long. Remove about 1/2-inch of insulation from each end.
Connect the end of one wire to the unregulated power supply's positive output terminal. Set the other end so it connects to the 7805's input pin. Connect the end of another wire to the power supply's negative terminal. Insert the other end so it connects to the regulator's middle pin. Insert a third and fourth wire so they connect to the 7805's middle and output pins, respectively.
Connect the free ends of the third and fourth wires to a circuit requiring 5 volts at up to 1 amp of current. The wire connected to the output pin has positive polarity; the other wire is a supply ground.
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