Category: 11. Transistor

FET constant current sources use JFETs and MOSFETs to deliver a load current which remains constant despite changes in load resistance or supply voltage. An FET Current Source is a type of active circuit which uses a Field Effect Transistor to supply a constant amount of current to a circuit. But why would you want a constant current? Constant current…

The Darlington Transistor configuration of two bipolar transistors offers increased current switching for a given base current. The Darlington Transistor named after its inventor, Sidney Darlington is a special arrangement of two standard NPN or PNP bipolar junction transistors (BJT) connected together. The Emitter of one transistor is connected to the Base of the other to produce…

We can summarise the main points in this transistors tutorial section as follows: Having looked at the construction and operation of NPN and PNP bipolar junctions transistors (BJT’s) as well as field effect transistors (FET’s), both junction and insulated gate, we can summarise the main points of these transistor tutorial as outlined below: Transistor Tutorial…

MOSFET’s make very good electronic switches for controlling loads and in CMOS digital circuits as they operate between their cut-off and saturation regions. We saw previously, that the N-channel, Enhancement-mode MOSFET (e-MOSFET) operates using a positive input voltage and has an extremely high input resistance (almost infinite) making it possible to use the MOSFET as…

Metal Oxide FET’s operate the same as JFET’s but have a gate terminal that is electrically isolated from the conductive channel. As well as the Junction Field Effect Transistor (JFET), there is another type of Field Effect Transistor available whose Gate input is electrically insulated from the main current carrying channel. The MOSFET is a…

The Junction Field Effect Transistor, or JFET, is a voltage controlled three terminal unipolar semiconductor device available in N-channel and P-channel configurations. The Junction Field Effect Transistor is a unipolar device in which current flow between its two electrodes is controlled by the action of an electric field at a reverse biased pn-junction. In the Bipolar…

Transistor switches can be used to switch a low voltage DC device (e.g. LED’s) ON or OFF by using a transistor in its saturated or cut-off state. When used as an AC signal amplifier, the transistors Base biasing voltage is applied in such a way that it always operates within its “active” region, that is…

The PNP Transistor is the exact opposite to the NPN Transistor device we looked at in the previous tutorial. Basically, in this type of PNP transistor construction, the two interconnected diodes are reversed with respect to the previous NPN transistor. This produces a Positive-Negative-Positive type of configuration, with the arrow which also defines the Emitter terminal pointing inwards in the…

NPN Transistors are three-terminal, three-layer devices that can function as either amplifiers or electronic switches. In the previous tutorial we saw that the standard Bipolar Transistor or BJT, comes in two basic forms. An NPN (Negative-Positive-Negative) configuration and a PNP (Positive-Negative-Positive) configuration. That is: an NPN transistor and a PNP transistor types. The most commonly used transistor configuration is the NPN Transistor.…

The Bipolar Junction Transistor is a semiconductor device which can be used for switching or amplification. Unlike semiconductor diodes which are made up from two pieces of semiconductor material to form one simple pn-junction. The bipolar transistor uses one more layer of semiconductor material to produce a device with properties and characteristics of an amplfier. If we…