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![]() This type of transistor biasing arrangement is also beta-dependent biasing as the steady-state condition of operation is a function of the transistors beta β value, so the biasing point will vary over a wide range for transistors of the same type as the characteristics of the transistors will not be exactly the same. This two resistor biasing network is used to establish the initial operating region of the transistor using a fixed current bias. The circuit shown is called as a “fixed base bias circuit”, because the transistors base current, I B remains constant for given values of Vcc, and therefore the transistors operating point must also remain fixed. Hence the Q point can be adjusted just by changing the value of the resistor connected to the base. And by using the current gain (β) relationship, I C can also be found out accordingly. Thus, by merely changing the value of the resistor the base current can be adjusted to the desired value. In this condition, a single power source is applied to the collector and base of the transistor using only two resistors. Fixed Base Biasing a Transistor: Fixed Base Biasing in BJT One of the most frequently used biasing circuits for a transistor circuit is with the self-bias of the emitter-bias circuit where one or more biasing resistors are used to set up the initial DC values of transistor currents, ( I B ), ( I C ) and ( I E ). In other words, the output current flows for the full 360 o of the input cycle. This mode of operation allows the output current to increase and decrease around the amplifiers Q-point without distortion as the input signal swings through a complete cycle. When a bipolar transistor is biased so that the Q-point is near the middle of its operating range, that is approximately halfway between cut-off and saturation, it is said to be operating as a Class-A amplifier. This central operating point is called the “Quiescent Operating Point”, or Q-point for short. The correct biasing point for a bipolar transistor, either NPN or PNP, generally lies somewhere between the two extremes of operation with respect to it being either “ fully-ON” or “fully-OFF” along its load line. Transistor Biasing Transistor Biasing:Įstablishing the correct operating point requires the proper selection of bias resistors and load resistors to provide the appropriate input current and collector voltage conditions. To make it less of a hassle, we can insert a toggle switch in the circuit so that we can just toggle the lever of the toggle switch if we want to turn ON or OFF the light bulb, instead of connecting or disconnecting the electrical plug.Transistor Biasing is the process of setting a transistors DC operating voltage or current conditions to the correct level so that any AC input signal can be amplified correctly by the transistor. So to turn ON the light bulb, we’ll insert the electrical plug to the outlet and to turn it off, we’ll disconnect the plug from the outlet. I hope you can imagine it, in reality, the light bulb is connected to the AC mains or wall outlet through an electrical plug and zip-cord. In figure 3, we can see a schematic diagram of a light bulb connected directly to the AC mains. So basically, an SPST toggle switch is simply an ON-OFF switch with two terminals (A & B) that can be connected together or disconnected from each other by toggling the lever (actuator). An SPST switch has one pole and one throw, so it can only control one circuit and its pole can be connected to one terminal only. The number of poles in a switch determines how many separate circuits the switch can control while the throw-count of a switch tells us how many positions each of the switch’s poles can be connected to. In figure 2, you can see a single-pole, single-throw (SPST) toggle switch and the circuit symbol of an SPST switch. A switch is an electrical or electronic device that can open or close a circuit, stopping or allowing the flow of current in a circuit.
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