![]() In the saturation mode, a transistor acts like a closed switch. To turn on an NPN transistor in cutoff mode, the base voltage must exceed 0.7V or higher. The collector-emitter path will not conduct in this state since no electrons are injected into the base region to be amplified by the collector current. This occurs when the base voltage is less than 0.7V and the current through the emitter-base junction is virtually zero. When in cutoff mode, a transistor functions like an open electrical switch. This is the most common use of transistors and they can be found in a variety of electronic circuits. In active mode, transistors are used to amplify signals. Operating Modes of Transistors Active Mode However, due to their construction, FET transistors have a much higher input impedance than BJT transistors which makes them less suitable for use in analog applications where high gain is required. FETs are commonly used as switches in digital circuits because they can be controlled by voltage or current sources and require very little current to operate. They are relatively easy to control and require less power for switching than BJT transistors. On the other hand, FETs have four terminals – Gate, Source, Drain and Body. This type of transistor works well for low power applications but requires more voltage for switching than a FET. ![]() Acting like an electrical switch, a current passing through the base terminal enables electrons to flow between collector and emitter terminals. īefore we can identify the most suitable method of using a transistor as a switch, we must first gain insight into the two predominant types of transistors employed for this purpose: BJT (Bipolar Junction Transistor) and FET (Field Effect Transistor).Ī BJT consists of three terminals – Collector, Base and Emitter. In addition, they are also commonly found in amplifiers, power supplies and other audio equipment. Transistors are widely used in computing applications such as memory storage, logic gates and integrated circuits. By controlling the amount of electric current that flows through a circuit, transistors can be used to amplify or reduce signals in electrical circuits. It acts as a switch, allowing electric current to flow through the circuit when the switch is on and blocking it when the switch is off. You can also check various touch switch circuits.A transistor is an electronic device consisting of three terminals, which are used to control electric current and voltage within a circuit. The touch plate must be made from copper, you can either use a copper plate or copper wire. This voltage developed across resistor R 2 de-energized the relay RL 1 and the further electrical or electronic appliances are de-activated. Similarly, when touch plate TP 2 is touched Darling pair (transistor T 2 and T 3) becomes high as a result voltage is developed across resistor R 2. ![]() When touch plate TP 1 is touched, the base voltage V be of transistor T 1 and T 2 becomes high which energized the relay RL 1 as a result electrical or Electronics appliance is activated. The Darlington configuration is equivalent to a single NPN transistor having, but almost twice the value of base voltage. To increase the current gain of the output-state transistors, and thus reduce the required base current drive, the Darlington configuration is frequently used to replace the NPN transistor. The transistor is biased for active region operation. Darlington pair of the transistor is a combined unit of two emitter follower circuits that are connected in cascade and enclosed as one package. Here, also we are using a transistor for amplification. As the input resistance of the circuit is high and also this type of circuit requires high current gain thus we used the Darlington pair transistor.Ī transistor may serve various functions but basically, it is used to amplify an electrical signal. Transistors T 2 and T 3 are configured in the Darlington pair. ![]() This circuit is designed using four general-purpose low-power NPN transistors. The circuit of the touch switch is shown in figure 1. Circuit Description of Touch Switch Circuit The circuit posted here used two individual switches for ON and OFF. you can on and off the lamp by simply touching the touch plate. The thing that motivates me to write this post is touch facilities i.e. A few days earlier I bought a reading lamp from one of the Chinese stores, the design of the Chinese product is quite impressive.
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