Hands-On-Physics

Introductory Electronics Unit
Core Project:
ACTIVITY #1


A low voltage power supply (LVPS) controls voltage within a safe range. The voltage from a household outlet is NOT in a safe range, as you know if you've ever been shocked by it. This circuit will reduce the voltage and convert it from AC (alternating current) to DC (direct current). You will be able to select between 1 and 17 volts by twisting a potentiometer. A potentiometer (pot) is like a dimmer switch. This circuit wil be useful in later projects.

Building the circuit

Examine the circuit diagram and picture of the circuit below. Notice that the top bus is used for the positive side of the circuit, and people generally use red wires there. The bottom bus is the negative side of the circuit, usually wired in black. In the middle a third color of wire is used. This lets someone else proofread and understand your circuit more easily.

Its important to wire the capacitors in the correct direction. Its also a good idea to keep your components spread out a little; this makes them easier to move, and it allows any heat to dissipate.


Use a short length of stripped wire to make an arch so the clip leads from the transformer can be easily attached. (See sketch above)

GET A FRIEND TO PROOFREAD YOUR CIRCUIT. Then, have the teacher check it before plugging it in.

To see if it works, hook your multimeter up to the output, and set it for DCV. Adjusting the pot should give you a variety of readings between 1 and 17 V. If the pot is turning the wrong way to adjust the voltage up, switch the pot leads in the circuit board.

If it works first try, congratulations!! You're unusually good.

If it doesn't, don't panic. Check your connections and proof read your circuit once again. Then check for any places the wires are touching where they shouldn't (a short). Then try it again. If it still doesn't work ask your teacher for help. Either you made a mistake or one of your components isn't working.


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