— PHYS 375: Lab 10 – Transistors Switches and Amplifiers –PurposesGet familiar with applications of transistor to controls.1 Variable Voltage DividerBuild the circuits shown in Figure 1 using a 2N5485 field effect transistor. The two sources Vddand Vcontare variable voltage sources1. Explain how the circuit constitutes a varia ble voltage divider.2. Set Vcont= 0 V and measure Voutfor Vdd= 1, 2, 3, and 4 V.3. Compute the equivalent resistance RDS(see handouts) for each of the values of Vcont.4. Repeat measurement fo r Voutfor Vdd= −1, −2, −3, and -4 V.5. For which value of Vcontthe FET does not act as a resistor anymor e .Vdd100 kWRD=1 kWVcont100 kWFigure 1: Circuit for part 1.2 Fast switchBuild the circuit shown in Figur e 2. Use a BJT transistor 2N3725 or equivalent.1. Use a DC voltage source to provide 5 V. Close the switch and measure VCE, the voltage drop acrossthe resistor and deduce ICand IB.2. Replace the resisto r with a 150 Ω resistor and redo the measurement.3. Use a function generator as voltage source instead of the DC source. Set the ge nerator to pro ducesquare wave with amplitude of 5 V approximately.11 kW+5 VDMMlampFigure 2: Circuit for part 2.4. Vary the frequency and describe your observations.5. Set the freq uency to f = 100 kHz and observe, describe and interpret the collector voltage with thehelp of an oscilloscope. Measure the the rise and fall time of the transistor switch and conclude onthe limitations/potentials of such a switch.3 Light emitting diodeBuild the circuit shown in Figur e 3. Use a variable DC voltage power supply for V.1. Adjust the powe r supply to get a voltage across the resistor VR= 5 0 mV2. Measure the voltage drop across the diode3. Repeat Step (2) for VR= 0.1, 0.5, 1, 2,and 5 V4. Plot current current versus voltage for the dio de5. How much current is needed to turn the diode on.VR=330 WVRVDFigure 3: Circuit for part
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