Transistor – ubiquitous and important component in modern microelectronics. Its purpose is simple: it allows you to use the small-signal control is much stronger.
In chastnoti, it can be used as a controlled “choke”: the absence of the signal at the “gate” to block the flow of current, flow – allow. In other words, this is the button that is pressed is not a finger, and energizing. In digital electronics such use is most prevalent.
Transistors are available in different packages: one and the same transistor may outwardly look totally different. In prototyping enclosures occur more frequently than others:

TO-92 – a compact, small loads

TO-220AB – a massive, good heat dissipation for large loads

The diagram also varies depending on the type of transistor and standard notation that was used in the preparation. But regardless of the variation, it remains recognizable symbol.


Bipolar transistors

Bipolar Transistors (BJT, Bipolar Junction Transistors) have three contact:

collector – it is fed a high voltage, which wants to manage

Base – through it served a small current to unlock big; base is grounded to block it

emitter – current flows through it from the collector and the base, when the transistor is “open”


The main characteristic of the bipolar transistor is a component h fe is also known as the gain. It reflects how many times more current to the collector-emitter transistor capable miss relative to the base-emitter current.
For example, if h fe = 100, and passes through the base of 0.1 mA, the transistor to pass through itself as a maximum of 10 mA. If in this case on the portion with a large current is a component that consumes example 8mA, he will be given 8 mA, while the transistor remains “margin.” If there is a component that consumes 20 mA, it will be provided only a maximum of 10 mA.
Also, the documentation for each of the transistors the maximum permissible voltages and currents at the terminals. Exceeding these values ??leads to excessive heat and reduce service, and a strong excess can lead to destruction.


The above-described transistor – the so-called NPN-transistor. It is called so because of the fact that it consists of three layers of silicon, connected in the order: Negative-Positive-Negative. Where negative – an alloy of silicon, which has an excess of negative charge carriers (n-doped), and positive – with an excess of positive (p-doped).
NPN more efficient and widespread in industry.


PNP-transistors in the designation differ in the direction of the arrow. The arrow always points from P to N. PNP-transistors differ “inverted” behavior: the current is not blocked when the base is grounded and locked when the current goes through it.

Field-effect transistors

Field effect transistors (FET, Field Effect Transistor) have the same purpose, but differ internal device. The private views of these components are transistors MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor). They allow you to operate much more power with the same dimensions. A control most “flap” is carried out exclusively by means of voltage: the current through the gate, unlike bipolar transistors, is not.

Field-effect transistors have three terminals:

drain – it is fed a high voltage, which wants to manage

gate – it is energized to allow the flow of current; gate grounded to block current.

source – current flows through it with the flow, when the transistor is “open”


N-Channel and P-Channel

By analogy with bipolar transistors, field different in polarity. Has been described N-Channel transistor. They are most common.
P-Channel when referring to different direction of the arrow and, again, has an “inverted” behavior.


According to the materials

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