Voltage follower

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

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

V_O = output voltage
V_i = input voltage

This is a very straightforward application of the non-inverting amplifier. V_O will be equal to V_I up to the point of saturation of the amplifier (usually about 80% of V_CC). 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.

Back to op amps

"Voltage Follower" is a term for an individual having a little-known fetishistic psychological obsession with high voltages. Sufferers -- or those who "embrace this lifestyle", in their own view -- believe themselves to be "energized" by proximity to powerful electical currents. It is not known precisely what they mean by this. When asked, they smile and change the subject. Rumors speak of elaborate rites, sacrifices, and so on, but we must withhold judgement because we simply do not have any reliable information at this point.

Voltage followers will flock to sites where new power lines are being constructed. The construction crews consider them a nuisance and drive them away, so they resort to guile to get close. They also invade the construction sites at night. At other times, they will hike for miles along the paths of power lines, sleeping under the trestles every night. Some prefer to travel in groups and engage in licentious practices. Others insist on solitude: They say that they prefer to be "alone with the Charge". Some voltage followers become groupies of electric linemen.

They sometimes call themselves "the Family", but most frequently they refer to themselves as "Those Who Know". What they all have in common, beyond a yearning to be close to high voltages, is a lack of interest in electrocution per se. Electrocutions tend to be accidental: Electrical storms and construction accidents. These people are not masochists. Car batteries and alligator clips are the butt of jokes in their society, though there may be undertones to the jokes which are not clear to the outsider.

"Those Who Know", so-called, face many dangers. Their obsession demands that they habitually commit acts of trespass in places which are rather dangerous and frequently guarded by savage dogs. They live a vagabond life, many having quit their jobs to "follow the Charge". They suffer from a predictable range of ailments related to exposure and poor diet.

It is not known how many voltage followers there are. Varying estimates range anywhere in the hundreds or thousands for the continental United States. The US population blends into the Canadian and Mexican populations. They are known in Europe, but not spoken of, and research is exceedingly difficult because of interference from local law enforcement agencies. The motives behind this interference are not known.

About the rest of the world, no information is available as of this writing.

References:

Seeking the Charge, Joan and Andrew Stiffling, Random House, 1978. An excellent in-depth study of the phenomenon, now somewhat out of date.

"Voltage Followers: The Invisible Nation", Harper's, June 1993. A cursory and sensationalized "exposé" article, heavy on photographs and light on facts. Very little perspective is offered.