12/19/2023 0 Comments Transistor switch![]() ![]() The direction of the transistor arrow is the current direction. Ⅱ Transistor Characteristicsġ) IB controls IC. Diffusion motion forms emitter current IE, recombination motion forms base current IB, and drift motion forms collector current IC, where IE=IC+IB. The purpose is to collect electrons to generate a large current, which forms an amplification effect on the base current. 4) The collector has a large area, which helps to collect the electrons emitted by the emitter, so it is called the collector. The electric field force will drift to the collector. When the electrons from the emitter junction come over, there is little recombination with the base here, resulting in the base current IB, and most of the electrons are received. 3) The concentration of many electrons in the P region of the base is holes, the concentration is low and very thin. 2) The emitter process is characterized by high concentration, so when the emitter junction is forward biased, a large amount of electrons will be emitted, so it is called an emitter. Some people say how can holes move? That is due to the recombination of electron movement and hole, which is easy to understand from the macroscopic point of view as the hole is moving. A transistor has three poles, three regions, and two PN junctions (observing the structure of it helps to understand how it works.ġ) The hollow in the figure is positively charged for holes, and the solid ones are negatively charged for electrons. ![]() The transistor is a current-type control device, similar in function to the field effect transistor ( FET), and can be used as signal amplification, oscillation and modulation. Unlike ordinary mechanical switches (such as relay, switch), transistors use electrical signals to control their own opening and closing, so the switching speed can be very fast.ĥ.1 Waveform Analysis of Basic Common Emitter Amplifier Circuitĥ.2 Feasibility and Necessity of Transistor Switch Circuit DesignĦ.1 Basic Switching Circuit of NPN TransistorsĦ.2 Basic Switching Circuit of PNP Transistors It is a variable current switch capable of controlling the output current based on the input voltage. The transistor is fully – ON and operates as closed switch.A semiconductor transistor is used to amplify, control, and generate electrical signals and power. The transistor operating in the saturation region exhibits following characteristics −īase – Emitter voltage is greater than cut – in voltage (0.7 V).īoth the base – emitter junction and base – collector junction are forward biased. The collector current I C = 0 A and output voltage V out = V CC. The transistor is fully – off acting as open switch. The V BE is less that cut – in voltage 0.7 V.īoth emitter – base junction and collector – base junction are reverse biased. When transistor operates in the cut off region shows the following characteristics − Circuit Diagram of Transistor as a Switch Cut Off State (Open Switch) ![]() Therefore, both the on – state and off – state power loss is zero in the transistor switch. When the transistor operating as switch, in the cut off region the current through the transistor is zero and voltage across it is maximum, and in the saturation region the transistor current is maximum and voltage across is zero. If a positive signal applied at the input terminal then it acts like a closed switch. When a zero input signal applied to the base of the transistor, it acts as an open switch. The transistor operates as a Single Pole Single Throw (SPST) solid state switch. If the transistor is operated in the saturation region then it acts as closed switch and when it is operated in the cut off region then it behaves as an open switch. A transistor can be used as a solid state switch. ![]()
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