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# An Investigation of Transistor Current in Npn and Pnp Bipolar Junction Transistors

Purpose The objective of this lab is to introduce the Bipolar Junction Transistor BJT A BJT is a three terminal device composed of an emitter base and collector terminals In this lab we will introduce two major types of BJTs npn and pnp The first npn has an n-type emitter a p-type base and a n-type collector On the other hand the pnp has a p-type emitter a n-type base and a p-type collector Also the transistor consists of two major pn junctions the emitter-base junction EBJ and the collector-base junction CBJ Depending on the bias condition of each of these junctions there are different modes of operation We will show that the basic principle of a BJT is the use of the voltage between two terminals on order to control the current in the third terminal Activity One Diagram of a npn BJT 2N3904 Theory In this part of the lab we will use the curve tracer to display the common-emitter BJT family of curves We will see the i-v characteristics of Ic vs Vce for steps of IB The i-v characteristic showing Ic vs Vce for different values of VBE are not linear Thus we will see that the output resistance of the BJT change slightly with current Then using the values of Ic and Ro we can calculate the early voltage Va The important feature of this device is that the i-v characteristics are not perfect linear Data Section Outline of procedures 1 Use the curve tracer to display the common-emitter BJT family of curves ic vs vCE for steps of iB 2 Determine IB needed to set the Q-Point for Ic05mA and VCE5 Volts 3 Determine DC 4 Determine AC ICIB 5 Determine the output resistance Ro by measuring the slope of the i-v curve and taking the inverse of that 6 Does

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