The collector current, Ic, of a transistor is the amplified output current of a bipolar junction transistor. How to Calculate the Emitter Current IF of a BJT Transistor The transistor parameters for the circuit in Figure P6.77 are vbeta1 = 120, beta2 = 80. β = I C /I B A voltage of 5 V is applied between collector and base. The first step for me seems to understand the quiescent status of the circuit. To ensure faithful amplification, the following basic conditions must be satisfied. For negative half cycle, the same junction gets reverse biased and hence the circuit doesn’t conduct. Vc… Has less slope than the dc load line c. Is steeper than the dc load line A similar circuit is shown in the figure below. Above Equation shows that the collector current is dependent to some extent on β DC and V BE. If the operating point is considered near saturation point, then the amplification will be as under. If the base current, Ib, and β are known, then Ic can be computed by the following formula: Example If Ib=35μa and β=100, then Ic calculates out to be: 2nd Way to Calculate Collector Current Ic. The attached is a simplified circuit without feedback caps/etc, and the simulation shows quiescent current/voltage pretty close to what the circuit is … But for the transistor to function properly as an amplifier, its input circuit (i.e., the base-emitter junction) remains forward biased and its output circuit (i.e., collector-base junction) remains reverse biased. Here output current is collector current and input current is base current. How to Calculate GmVπ of a BJT Transistor Circuit So if VCE is greater than VKNEE the collector-base junction is properly reverse biased and the value of β remains constant, resulting in faithful amplification. Hence the quiescent point or Q-point is the value where the Faithful Amplification is achieved. If the operation point is considered near cut off point, then the amplification will be as under. We know that the emitter current is the sum of small base current and large collector current. The base-emitter junction is forward biased and the collector-emitter junction is reverse biased. The simplest biasing applies a base-bias resistor between the base and a base battery VBB. Taking a base current of 20uA and reading values direct from the output curves, the collector current, for a collector emitter voltage of 10 volts is around 3.9mA. Divide the collector current by P to find approximately what the base current should be. it all depends on what information is already known about the transistor: If the base current, Ib, and β are known, then Ic can be computed by the following formula: Example This can be understood as Faithful Amplification. The circuit shown in Figure 6-51 is the common emitter amplifier configuration, because the input signal is applied to the base terminal and the output is taken across the collector terminal. Find α, I E and I B when collector current is 1 mA. (c) Determine the input and output resistances Rib and Ro. I C = αI E. I B = I E – αI E. I B = I E (1-α) β = DC current gain for common emitter circuit = Output current/Input current. Class A amplifiers have the general property that the output device(s) always carry a significant current level, and hence have a large quiescent current. The various parameters are as follows. The emitter is common to the both base and collector terminals, and it is grounded.Write the expression for the quiescent power dissipation. A basic, low-frequency hybrid-pi model for the bipolar transistor is shown in figure 1. If the base-emitter voltage VBE is greater than this voltage, the potential barrier is overcome and hence the base current and collector currents increase sharply. ⇒ STABILISATION BUT RE also: This dependency, of course, can be minimized by making R C >> R B /β DC and V CC >> V BE. Remember that those conditions should be relatively insensitive to temperature changes, as well as parameter variations from device to device. The transistor’s power rating must exceed this value. The biasing of the transistor in class B operation is in such a way that at zero signal condition, there will be no collector current. Base current is only 2% of the emitter current I e while the remaining electrons will flow from the reverse bias collector junction known as Collector current (i c). There can be many such intersecting points, but the Q-point is selected in such a way that irrespective of AC signal swing, the transistor remains in the active region. What is Open Collector Output (of a BJT Transistor). termine the ideal quiescent collector voltage and current. A typical beta is around 290. if the emitter current starts to rise as a result of some change in the transistor’s characteristics, then the voltage across RE rises accordingly. The values of Beta vary from about 20 for high current power transistors to well over 1000 for high frequency low power type bipolar transistors. This operating point is also called as quiescent point or simply Q-point. Quiescent Collector Current I q Quiescent Collector Current I q = _____mA 4. Find the collector voltage VC. VBE1 (on) = VBE2 (on)= 0.7 V, VA1 = VA2 = infinity (a) Determine the quiescent collector current in each transistor. The minimum voltage needed for a silicon transistor to conduct is 0.7v and for a germanium transistor to conduct is 0.5v. The fulfillment of these conditions ensures that the transistor works over the active region having input forward biased and output reverse biased. There are several ways to find the collector current, Ic, of a transistor. IE =IC+ IB. How to Calculate GmVπ of a BJT Transistor Circuit. Calculate the Collector current (Ic) flowing through the load resistor when the transistor is switched fully "ON", assume Vce = 0. Hence the placement of operating point is an important factor to achieve faithful amplification. Q-Point Stability Over Temperature . How to Calculate Rπ of a BJT Transistor The dc quiescent power, given in Equation 7–3, is the maxi-mum power that a class A amplifier must handle. To achieve a faithful amplification, the collector emitter voltage VCE should not fall below the cut-in voltage, which is called as Knee Voltage. If VCE is lesser than the knee voltage, the collector base junction will not be properly reverse biased. How to Calculate VBB of a BJT Transistor Hence the quiescent point or Q-point is the value where the Faithful Amplification is achieved. If Ie=4ma and β=150, then the value of Ic is computed to be: Using Known Values In a transistor circuit, the quiescent state is defined by the voltages and currents present in the circuit when the power supply is … The collector current, along with the base current, is a product of the energy produced through the emitter circuit, which is divided at the base current… From the h-parameter circuit, it can be determined that the emitter and base currents are related through the dependent current source by the constant hfe+1. All the four h-parameters for any transistor configuration, namely CE, CB and CC, vary with variation of collecto0r current I C and collector junction temperature. DC Amplifier. This is done when AC signal is applied at its input. The ac load line usually a. ... formula for a filter corner frequency for 20kHz gives: % = [P o(rms) / P dc] 100% Procedure 1. Value of the load resistor R L using half the supply voltage V CC divided by I C R L = _____ Ω V Nearest preferred value = _____ Ω 5. A collector current is referred to when identifying the output current from the transistor to the transistor’s collector terminal. This in turn lowers the base-emitter voltage of the transistor, tending to bring the emitter current back down towards its original value. If base current, Ib, and emitter current, Ie, are known, then Ic can be calculated by the formula: Example The magnitude of this voltage should be such that the base-emitter junction of the transistor should remain in forward biased, even for negative half cycle of input signal. Base current and large collector current Ic supply power supplied to amplifier 3 needed for a germanium transistor the! 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