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How to Generate a Negative Voltage

Negative voltages are required to help power electrical components, such as op amps, which are semiconductors used to amplify signals. A negative voltage may be produced from two or more batteries joined together in series. Another way to generate a negative voltage is to use a linear IC. A linear IC is a semiconductor built to provide stable voltages. The LM9XX series IC can supply amounts such as --15 volts, and can handle up to 1 of current. The LM7905, for example, can supply --5 volts. Capacitors must be placed on its input and output to help control noise.

Things You'll Need

LM7905
0.1uF tantalum capacitor
10uF tantalum capacitor
9V battery
Breadboard
Jumper wire
Digital multimeter

Instructions

- 1
  Choose one row on the breadboard for ground or zero voltage, and another one for the voltage source. Connect the battery in reverse. Attach the plus side of the battery as ground, and the minus side as the power source.
- 2
  Insert the LM7905 IC horizontally into the breadboard. Each pin must fall into a different column. Typically, the pin on the left is ground or pin 3, the middle is the input or pin 1, and the output is pin 2 on the right.
- 3
  Attach one end of a jumper wire to pin 1, and place its other end in the power source row. Add one end of the 10uF capacitor to the pin 1 column, and place its other end at ground. If the capacitor is electrolytic, its negative lead must be the one that is attached to pin 1.
- 4
  Attach the 0.1uF capacitor so that one side is at pin 2, and the other side is at ground.
  
  Insert a jumper wire between pin 3 and ground.
- 5
  Place the battery inside of the holder, and then measure the output voltage at pin 2. To do this, first place the multimeter on a DC voltage setting. Place its red lead on the left side of the capacitor at pin 2, and its black lead on the capacitor's right side. A representative reading is -5.01 volts.

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