PNPN structure

Thyristor stems from the Greek word meaning 'door'. Perhaps so named because of the nature of this component is similar to that door can be opened and closed to pass an electric current. There are several components that include, among others thyristor PUT (programmable uni-junction transistor), UJT (uni-junction transistor), GTO (gate turn off switch), photo SCR and so on. But on this occasion, which will point out the components of the thyristor known as SCR (silicon controlled rectifier), TRIAC and DIAC. Readers can listen to more clearly how the working principles and their application.
thyristor structure
The main characteristics of a thyristor is a component made of silicon semiconductor material. Although the material is the same, but its PN junction structure is more complex than a bipolar or MOS transistor. Thyristor component is more used as a switch (switch) rather than as an amplifier as well as current or voltage transistor.

Basic structure of the thyristor is a four layer PNPN structure as shown in the figure above a. If sorted, this structure can be seen as two PNP and NPN junction structure are connected in the middle as shown above b. This is nothing but the two PNP and NPN transistors are connected to each collector and base. If visualized as transistors Q1 and Q2, then the thyristor structure can be displayed as shown below.



Seen here is connected to the collector of transistor Q1 base of transistor Q2 and the collector of transistor Q2 is connected opposite the base of transistor Q1. Such a transistor circuit indicate a strengthening of the current loop in the middle. Where b is known that Ic = Ib, the collector current is the strengthening of the current base.
If for example there is a current of Ib flowing to the base of transistor Q2, then there will be current Ic flowing in the collector of Q2. This collector current is the base current Ib to the transistor Q1, so it would appear on the strengthening of the current collector of the transistor Q1. Tdak transistor Q1 collector current is the current base of another transistor Q2. So forth so that the longer the PN connection of the thyristor is in the middle will shrink and disappear. Left is the P and N layers on the outside.
If this condition is reached, then such a structure is the structure of the swordfish another PN diode (anode-cathode) are already known. At such a time, called the thyristor is ON and the current can flow from the anode to the cathode such as a diode.



What if we give in this thyristor dc lamp load and rated supply voltage from zero to a certain voltage as shown above. What happens to light when a voltage is increased from zero. Yes yes, of course, the lights will remain off for the middle layer of the existing NP will get a reverse-biased (diode theory). At this time called the thyristor is turned OFF because no current can flow, or very small. Current can not flow through a reverse-bias voltage that causes certain connections and missing NP is saturated. This voltage is called breakdown voltage and current at the time it began to flow through diode thyristor as large. At this voltage thyristor breakover voltage VBO called.