Lab Report 4 - ECE 342 Lab 4: BJT Current Sources and Sinks...

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ECE 342 Lab 4: BJT Current Sources and Sinks Stephanie Duy, Robert England Lab Group 4 November 14, 2007 Abstract This report describes the simulation, construction and test of three constant current sinks and a constant current source using bipolar junction transistors. The first current sink configuration connects the emitters of both transistors to ground with 1 kΩ resistors, and sinks 1.54 mA. The second current sink configuration connects the emitters of both transistors directly to ground, and sinks 1.51 mA. The third configuration is a hybrid of the first two; one transistor has its emitter grounded while the other emitter is connected to ground with a 1 kΩ resistor, and the circuit sinks 75.6 μA. The current source is based largely on the third configuration and generates a 51 μA current. All devices require +10 V power supplies. Component selection and test procedures are described. 1
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Contents 1 Introduction 3 2 Circuit Analysis and Design 4 2.1 Configuration 1 6 2.2 Configuration 2 7 2.3 Configuration 3 8 2.4 Current Source 9 3 Simulated Results 11 2.1 Configuration 1 11 2.2 Configuration 2 12 2.3 Configuration 3 13 2.4 Current Source 14 4 Experimental Results 16 2.1 Configuration 1 16 2.2 Configuration 2 18 2.3 Configuration 3 20 2.4 Current Source 22 5 Discussion 24 6 Conclusion 25 2
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1. Introduction This report describes the analysis and test of three configurations of a current sink, each with different resistor values, and the design and test of a similar current source. Each of these circuits was tested to find a reference current; the output voltage, current, and resistance characteristics; and the range of load resistances for which the circuit worked properly. The operation of each circuit was compared and contrasted, and the current source was tested for proper operation. Section 2 analyzes the current sinks and calculates theoretical values for the output current in each case; this section also details the design of the current source. Section 3 describes the simulation of each circuit and finds values for the output characteristics. Section 4 contains the experimental results of physical circuit prototypes and compares the experimental results with those found from the simulations. Section 5 discusses the differences between the various configurations and details the advantages and disadvantages of each circuit. 3
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A schematic of the current sink is shown in Figure 1 below. Figure 1: Current sink schematic Figure 2 below approximates a “good” current sink over a wide range of load resistances (R L ). Figure 2: Simplified model for the current sink given in Figure 1. For a “good” current sink, I O is predictable, and R O is very large. 4
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Lab Report 4 - ECE 342 Lab 4: BJT Current Sources and Sinks...

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