Diodes, Transistors and Thyristors

Diodes, transistors, and thyristors are all types of semiconductor devices. Diodes and transistors form the foundation of the modern era of personal computers and mobile electronics. They find wide-ranging application throughout the entire electronics industry. Virtually no useful electronic system can operate without them.
A diode is a two-terminal device. Diodes exist anywhere p-type, and n-type semiconductors are directly adjoined to each other. Applying a positive voltage to the anode will not produce any significant current until the diode's threshold voltage is exceeded. Once the threshold voltage is exceeded current will be allowed to flow from the anode to the cathode but the diode will block current flow from the cathode to the anode under most conditions. Diodes are used in AC-DC transformers, radios, electro-static discharge (ESD) circuits, as light sources, etc.
Transistors are perhaps the most ubiquitous of all semiconductor devices. These three-terminal devices can be made in bipolar junction (BJT) form, or more commonly as complimentary metal-oxide-semiconductor (CMOS). Adjoining n-type and p-type semiconductors in either the PNP or NPN configuration creates a transistor. Transistors are connected in various ways to create specific circuits. Typically a voltage is applied to a gate terminal allowing current to flow through the device where the transistor functions similarly to a switch. They are used in digital systems to implement logic gates and store data. Analog circuits use transistors to create amplifiers and oscillators.
The thyristor is another three-terminal semiconductor device that acts as a bistable switch conducting once their gate is charged and continuing to conduct while they are forward biased. The thyristor is built from four adjoined semiconductors in NPNP or PNPN format. They are often used in circuits with relatively large amounts of power. Unlike the transistor, a thyristor can only function as a digital switch.