|    VCC      |
               |     |       |
               |  |\ |       |
               |  |  \       |
               +--|-   \     |
                  |      >---+----VO
   VI ------------|+   /
                  |  /
                  |/ |

0 V ---------------------------------------o

VO = output voltage
Vi = input voltage

This is a very straightforward application of the non-inverting amplifier. VO will be equal to VI up to the point of saturation of the amplifier (usually about 80% of VCC). See Non-inverting amplifier for details on why it works.

The main reason to use one of these widgets is to sit between a source which can only provide a very small amount of current and a device which requires a moderate amount of current to operate. A good example is a circuit involving a thermocouple (which, although it can provide a voltage of several volts, can only output a miniscule current). Because the op-amp's input resistance is very high, the op-amp only draws a very small current from the thermocouple. However, since the op-amp itself can draw current from its own power supply, it will be able to supply the next device in the chain (for instance, a MOSFET or a logic chip) with the required amount of current for operation.

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