As switches, they are generally used in automatic control devices that may switch tens, hundreds, thousands, even millions of times per second. Often these take very feeble electrical output energy of remote sensors to cause the switching action, which switches circuits of much larger energy. This allows precision control without need for human interaction/intervention.
As amplifiers and other analog devices, they take take very small input signals and produce large output signals to drive broad cast speakers, recording devices, etc. Oscillators convert d.c. current to a.c. signals of specific frequencies.
The point is, that like a mechanical switch, a large amount of power can be controlled by a small one. With a mechanical switch, you can turn on a 5hp motor, much more power than you can supply with your finger or even your whole body. WIth a transistor, you can control something with microwatts of power. Not really much of a deal when you have a finger available. But when you have a very weak signal coming in from an antenna or a microphone, which is low voltage AND low current, that tiny signal can control a much larger one, one that's big enough to be heard through a speaker. And that transistor can switch in nanoseconds, much faster than a mechanical switch, which takes many milliseconds.
As a switch, a transistor is more like a relay, ie a small amount of power can control a much larger current, ie it is an amplifier.
In a logic circuit, transistors are wired in series and parallel so that they combine multiple signals in order to create a complex logic function, like adding two binary numbers. See AND and OR logic gates, etc.
Individual transistors are often not used as switches but as a variable ~resistance / valve in order to meter out a precise amount of current.
Mechanical switches are incredibly slow, and will fail after a few thousands of cycles of use. The early digital computers actually used relays (a special kind of switch) instead of transistors or tubes, like in WW2 the german Zuse Z3 (source).
Computers of that time could also be made with tubes and different feedback elements could "program" these early tube and magnetic amplifier based analog computers to perform rocket guidance computations (last source), or artillery aiming calculations. But analog computers were never as versatile as the digital computers.
Reliability, slow speed, weight, power consumption, and large size killed the relay based computer. They do have a few advantages, like immunity to radiation, so every so often someone develops an electro- mechanical miniaturized computing element.
The initial voltage comes from a simple circuit switch
your yes/no transistors will do the rest depending on what function you want to give your device
Another advantage of transistors is that they can be very small. Like, nano meters small.
hello
i can't understand this, they say that transistors are used to as switches, you have a circuit and a transistor on it, the transistor does not work until you apply voltage to it, how do you apply voltage? by turning on another mechanic switch.....does this make sense???
i'm going crazy with this, hope somebody can explain it simply
