MOSFET Lab

Purposes:

1. To investigate two circuits that can control the voltage across an electric motor.

2. To gain some insight into how DC brushed motors behave.

3. To control the power supplied to a motor with a MOSFET.

4. To regulate the behavior of a motor with a controller.

Materials:

N-type power MOSFET (IRF510 or NTE2382), 10kohm potentiometer, 2.2kohm resistor, 22-AWG wire, oscilloscope, 1N4007 rectifier 

Procedures:

Part 1: 

First we were required to construct the circuit shown in the schematic diagram shown below and to connect it to an oscillator. The second photo below shows the circuit itself. 

To begin, we were required to put the oscilloscope into storage mode and to set it for a single sweep. We made sure to set the vertical scale to 10 V/div as well as the time scale to 0.1mS/div. We adjusted the trigger level until we successfully started the motor. We indeed heard some off and on cycles. Next we attempted to neutralize the transients by putting a 1N4007 rectifier diode in parallel with the motor. We turned on the motor to investigate the effect of the diode onto the motor's cyclical sound. We did notice a longer cycle. 

Next we were required to construct the circuit in the diagram below which included the load resistor and the diode.  The photos below show both the schematic and actual circuits.

We noticed that the motor turned on at a gate voltage of 7.23 V. Next, we slowly increased Vgs from an initial value of zero. We noticed that with the increase in voltage, the motor begin spinning faster with the cycles being shorter. So I would definitely say that we were controlling the motor voltage well.  We measured the internal resistance of the multimeter and noticed that it had a value of 0.5 ohm. Then we were instructed to disconnect the motor from the circuit and to connect it onto the oscilloscope. We measured an induced back voltage of 8 V by hand.

Part 2: 

Now for the second part, we were to control the average voltage applied to the motor using pulse-width modulation.   

We were now required to replace the potentiometer with a 0-10 V square wave function generator and we set it to 10 kHz. We then used an oscilloscope to display the waveform of the voltage of the motor. Here is what we observed:

We now varied the duty cycle wave to 100% and noticed that the motor sped faster. The following photo shows proof that it sped faster. Notice how the cycles became shorter.

When then changed the DC source knob to 30% of maximum power and we made the following observation in the photo below:

Conclusion:

We considered this lab to be a success since we successfully completed all of our objectives. In all honesty, I thought that this was one of the most boring labs we've had all semester because it was based entirely on just observations without any data nor follow-up theoretical computations. 

Second Order Tutorial

The purpose of this assignment was to give ourselves an opportunity to supplement and reinforce what we've learned from our lecture and homework assignments regarding second order circuits. There were a total of 18 problems, plus an additional page summarizing our results. Please scroll down to view the screenshots of our results.

Problem #1

Problem #2

Problem #3

Problem #4

Problem #5:

Problem #6

Problem #7

Problem #8:

Problem #9:

Problem #10:

Problem #11: 

Problem #12: 

Problem 13:

Problem #14:

Problem #15:

Problem #16:

Problem #17:

Problem #18:

Problem #19:

As you can see, we were successful in our attempt to solve every problem correctly. I only wish our instructor would have shown us this tutorial page much sooner so that we could more easily familiarize ourselves with the mechanics of problem solving from previous chapters and sections. I really loved the fact that this tutorial gave us step-by-step guidance into solving the entire problem as a whole.

Complex MATLAB

To begin the complex analysis version of FreeMat we were introduced to the fact that FreeMat has numerous predefined variables. We were asked to type in pi and the variables i and j into the command window.

For Exercise 1, we were then instructed to create some variables and to give them some complex number values. Then we were instructed to create variables D = (A*B)/C and E=(A+B)*C. Here is what we obtained:

Next we were introduced to four functions angle(Z), abs(Z), imag(Z), and real(Z) that would allow us to make conversions from rectangular to polar and vice versa.

For Exercise 1, we were asked to create variables A=3+4j, B=3-2j, and C=2<50 and to define and to compute D=(A+C)/B.  Here is what we obtained:

We then computed the angle in degrees and the magnitude of variable D. he is what we obtained:

For Assignment 1, we were to assign variables A1=3+2j, A2=-1+4j, and B=2-2j. First, we were to manually compute C=(A1*B)/A2 and then confirm this by using FreeMat. Here is what we obtained:

We were then to convert C into polar form.

We were now instructed to repeat the assignment for D=(A1+B)*A2.

Next we were given a system of two equations with complex numbers. Here is the process we used to solve this equation:

Next, we were shown how to find the roots of functions using the "roots" formula. More specifically, in Exercise 1 we were told to find the roots of x^2+4x+3. Here is what we obtained.

Now for  Assignment 2, we were instructed to find the roots of a few more functions x^2+x+4, x^3+3x^2+3, and x^4+3x^3+4x^2+2x+7. Here is what we obtained:

Lastly, we were asked to find the roots of the denominator of a Laplace Transform function s^3+5s^2+7s+3. Here is what we obtained:

To sum things up, I really enjoyed this lab assignment as much as I did with the first MATLAB assignment. I am now equipped with the tools needed to solve problems using complex numbers and variables.