Regulator

Voltage regulator ICs are available with fixed (typically 5, 12 and 15V) or variable output voltages. They are also rated by the maximum current they can pass. Negative voltage regulators are available, mainly for use in dual supplies. Most regulators include some automatic protection from excessive current ('overload protection') and overheating ('thermal protection').
Many of the fixed voltage regulator ICs have 3 leads and look like power transistors, such as the 7805 +5V 1A regulator shown on the right. They include a hole for attaching a heatsink if necessary.
Please see the Electronics in Meccano website for more information about voltage regulator ICs.

Darlington pair

This is two transistors connected together so that the amplified current from the first is amplified further by the second transistor. This gives the Darlington pair a very high current gain such as 10000. Darlington pairs are sold as complete packages containing the two transistors. They have three leads (B, C and E) which are equivalent to the leads of a standard individual transistor

You can make up your own Darlington pair from two transistors

For example

• For TR1 use BC548B with h_FE1 = 220
• For TR2 use BC639 with h_FE2 = 40

The overall gain of this pair is h_FE1 × h_FE2 = 220 × 40 = 8800.
The pair's maximum collector current I_C(max) is the same as TR2

Field Effect Transistors

FET’s, are referred to as voltage driven devices which have a high input impedance.
Field Effect Transistors are further subdivided into two classifications: 1) Junction Field Effect Transistors,
or JFET’s, and 2) Metal Oxide Semiconductor Field Effect Transistors or MOSFET’s

Bipolar Junction Transistors

The most common type of transistor is a bipolar junction transistor. This is made up of three layers of a semi-conductor material in a sandwich. In one configuration the outer two layers have extra electrons, and the middle layer has electrons missing (holes). In the other configuration the two outer layers have the holes and the middle layer has the extra electrons

Layers with extra electrons are called N-Type, those with electrons missing called P-Type. Therefore the bipolar junction transistors are more commonly known as PNP transistors and NPN transistors respectively.

Bipolar junction transistors are typically made of silicon and so they are very cheap to produce and purchase

Types of transistor

There are two types of standard transistors, NPN and PNP, with different circuit symbols. The letters refer to the layers of semiconductor material used to make the transistor. Most transistors used today are NPN because this is the easiest type to make from silicon. If you are new to electronics it is best to start by learning how to use NPN transistors
The leads are labelled base (B), collector (C) and emitter (E

These terms refer to the internal operation of a transistor but they are not much help in understanding how a transistor is used, so just treat them as labels!

A Darlington pair is two transistors connected together to give a very high current gain.

In addition to standard (bipolar junction) transistors, there are field-effect transistors which are usually referred to as FETs. They have different circuit symbols and properties and they are not (yet) covered by this page

Simple Transistor Circuit

Pictured above is a very simple circuit which demonstrates the use of transistors. When a finger is placed in the circuit where shown, a tiny current of around 0.1mA flows (assuming a finger resistance of 50,000 Ohms). This is nowhere near enough to light the LED which needs at least 10mA. However the tiny current is applied to the Base of the transistor where it is boosted by a factor (gain) of around 100 times and the LED lights!

NEW Click here to view a worked example using a transistor in an example circuit with LEDs

How do Transistors Wor

A bipolar junction transistor has three terminals - Base, Collector, and Emitter corresponding to the three semi-conductor layers of the transistor. The weak input current is applied to the inner (base) layer. When there is a small change in the current or voltage at the inner semiconductor layer (base), a rapid and far larger change in current takes place throughout the whole transistor.

Pictured above is a schematic diagram of the more common NPN transistor. Below is an illustration of the same transistor using water rather than electricity to illustrate the way it functions

The illustration (from satcure-focus.com) shows pipework with three openings B (Base), C (Collector), and E (Emitter). The reservoir of water at C is the supply voltage which is prevented from getting though to E by a plunger. If water is poured into B, it pushes up the plunger letting lots of water flow from C to E. If even more water is poured into B, the plunger moves higher, and the flow of water from C to E increases.

Therefore, a small input current of electricity to the Base leads to a large flow of electricity from the Collector to the Emitter.

What is a Transistor

A Transistor is an semiconductor which is a fundamental component in almost all electronic devices. Transistors are often said to be the most significant invention of the 20th Century. Transistors have many uses including switching, voltage/current regulation, and amplification - all of which are useful in renewable energy applications.

A transistor controls a large electrical output signal with changes to a small input signal. This is analogous to the small amount of effort required to open a tap (faucet) to release a large flow of water. Since a large amount of current can be controlled by a small amount of current, a transistor acts as an amplifier.

A transistor acts as a switch which can open and close many times per second

The first working Transistor

Physicist Julius Edgar Lilienfeld filed the first patent for a transistor in Canada in 1925, describing a device similar to a Field Effect Transistor or “FET”

From 1942 Herbert Mataré experimented with so-called Duodiodes while working on a detector for a Doppler RADAR system. The duodiodes built by him had two separate but very close metal contacts on the semiconductor substrate. He discovered effects that could not be explained by two independently operating diodes and thus formed the basic idea for the later point contact transistor.
In 1947, John Bardeen and Walter Brattain at AT&T’s Bell Labs in the United States observed that when electrical contacts were applied to a crystal of germanium, the output power was larger than the input. Solid State Physics Group leader William Shockley saw the potential in this, and over the next few months worked to greatly expand the knowledge of semiconductors. The term transistor was coined by John R. Pierce. According to physicist/historian Robert Arns, legal papers from the Bell Labs patent show that William Shockley and Gerald Pearson had built operational versions from Lilienfeld’s patents, yet they never referenced this work in any of their later research papers or historical articles.
The name transistor is a portmanteau of the term “transfer resistor”.
The first silicon transistor was produced by Texas Instruments in 1954. This was the work of Gordon Teal, an expert in growing crystals of high purity, who had previously worked at Bell Labs. The first MOS transistor actually built was by Kahng and Atalla at Bell Labs in 1960