Lab 9: Transistors

I began this lab by first forking and then cloning the repository 2012-Physics-308L-Lab-8-Transistors from Dr. Koch. Within the downloaded repository one could find the PDF file for “Lab 4: Transistor Circuits” from Panitz.

Transistors as Diodes

Our first task was to measure the resistance of the different components of the 1N3904 Transistor. A diagram of one can be seen below.

 

 

 

 

 

 

 

 

 

B:C Junction – 2.812 kohm

B:E Junction- 2.957 k ohm

When the leads were reversed the current would not flow and this clearly demonstrated the behavior of transistors as two diodes in series.

Transistors as Switches

For the first day of this lab we simply followed the directions for the part 2 of the Panitz lab 4.

We constructed the following circuit.

 

 

 

 

 

 

 

 

 

 

 

 

An image of this from day one can be found here and an image of the circuit with the addition of the 10 kΩ resistor can be found here.

 

Daq board #121

Issues with several transistors left at station. When constructing the circuit the LED would fail to turn on

board # error

restarted LabView and error no longer occurred.

Initial setup

pic 2: w/ 10k ohm transistor

pic 3: off

pic 4: on

 

Readings

18.17 mA across LED while on (parallel) (incorrect)

10.63 mA ascross LEd while on series Correct

0 mA cross LED while off

current to base.

w/ 10 kohm resistor at A to ground .99 mA

w/ out 10 kohm resistor .50 mA (correct b/c did not need because DAQ board corrects itself)

 

 

 Bad Ass Part

From now on 10 kohm resistor is disconnected

given rise time 35 ns

moved resistor w/ purple 270  to end where emitter goes to ground

red wires channel 2 (e-c)

orange wires channel 1 (switch)

(green to DAQ)

56 ns (within order of magnitude)

270 (pic)

change probe to 1 x andcorresponding in osc

trigger menu

last pic

probe on channel 2 changed from 10x to 1x. Had to lower volts/div but reading that had similar level off was generated.

zoomed in and rise time was anout 36 ns

 

 

 

Lab 6/7: Diodes & Rectification


Materials

430 Ω resistor

1 kΩ resistor

5.1 kΩ resistor

 

 

 

 

Diode

Zener Diode

100 μF capacitor

 

 

LED

 

 

 

 

Wire Jumper Kit

 

Voltage Probe

 

 

 

Oscilloscope

 

 

 

Heathkit

 

 

 

 

 

 

 

Multimeter

 

 

 

 


 

 

 

Setup

The goal of this lab was to construct the different circuits diagrammed in Panitz notes PDF provided in the GitHub repository found at  2012-Physics-308L-Lab-6-Diodes-etc. and  then observe voltage across the 1 kΩ resistor while noting the waveform displayed on the oscilloscope. All voltage measurements listed below are measured across the 1 kΩ resistor unless explicitly stated otherwise. The above materials were gathered and I began following the instructions laid out in the Panitz notes.

Lab 7 addendum

For the second day of the lab Dr. Koch added additional materials to the GitHub repository for Lab 6. We needed to pull these additional files down to the desktop. To accomplish this I executed the following code in GitBash.

Code for GitHub Pull

I. Transformer Characteristics

In this section I made sure that I was certain of the way the breadboard of the Heathkit was  configured, which was in the usual manner. More importantly I familiarized myself with the Transformer Connections that would be an important part of all the circuits configured in the lab.

Transformer Connections

With a multimeter I measured the AC voltage across the secondary windings of the transformer to be ~30 V. Now, as I progressed with the experiment I did not take voltage readings with the multimeter but rather peak to peak voltage readings with the oscilloscope.

Peak- Peak Voltage Readings On Transformer Connection

DC: 42.8 V

AC:42.4 V

Below are photos of the oscilloscope displaying readings for a connection between the transformer’s central tap (CT) and one secondary lead. Additionally, there is also the oscilloscope showing the reading of the connections between the CT and both secondary leads on the same display.

 

Oscilloscope Reading of Single Waveform


 

 

Oscilloscope Reading of Both Waveforms

 

 

 

 

 

 

 

 

 

 

 

 

II. Half Wave Rectification

For this part of the experiment a half wave rectifier consisting of one 430 Ω resistor, one 1 kΩ resistor, and one 1N4002 diode was constructed on the Heathkit. It is important to note that silver bar on diode corresponds to the point of the arrow on the diode diagram. Both the diagram and the actual setup can be seen below.

 

Half Wave Rectification Setup

The following peak to peak voltage readings were taken across the 1 kΩ resistor.

DC: 14.8 V

AC: 14.8 V

Half Wave Rectification Oscilloscope Reading

In the have wave rectification the bottom half the single waveform is truncated and during the portions of where it should appear the voltage is instead equal to zero.

III. Full Wave Rectification

For this part of the experiment a full wave rectifier consisting of one 430 Ω resistor, one 1 kΩ resistor, and two 1N4002 diodes was constructed on the Heathkit.

Both the diagram and the actual setup can be seen below.

Full Wave Rectification Setup (added second diode)

 

The following peak to peak voltage readings were taken across the 1 kΩ resistor

DC: 14.8 V

AC: 14.8 V

Full Wave Rectification Oscilloscope Reading

In the full wave rectification the bottom halves of the two 180 degree opposed waveforms are truncated, resulting in the above image.

IV. Filtering

For this part of the experiment a filter consisting of one 430 Ω resistor, one 1 kΩ resistor, two 1N4002 diodes, and one 100 μF electrolytic capacitor was constructed on the Heathkit.

Both the diagram and the actual setup can be seen below.

 

Filtering Setup (added 100 μF capacitor)

 

The following voltage readings were taken across the 1 kΩ resistor.

 

Oscilloscope Reading of Filtering Circuit

DC Voltage Readings

Peak-Peak: 720 mV

Trough of Waveform: 13.2 V

Peak of Waveform: 14 V

AC Voltage Readings

Peak-Peak: 720 mV

Trough of Waveform: -380 mV

Peak of Waveform: 420 mV

The saw tooth nature of the waveform comes as a result of the filtering. With the capacitor in place the circuit act as a high pass filter who output starts to approximate a more DC like waveform output. This can also be observed as the DC reading had a midpoint of 13.2 V and the AC reading had a midpoint of 570 mV.

V. Zener Diode

For this part of the experiment a voltage regulator consisting of one 430 Ω resistor, one 1 kΩ resistor, two 1N4002 diodes, one 100 μF electrolytic capacitor, and one 1N5242B zener diode was constructed on the Heathkit.

Both the diagram and actual setup can be seen below.

 

Zener Diode Circuit (Incorrect)

 

 

 

 

Oscilloscope Reading of Zener Circuit Incorrect

Incorrect Orientation

DC Voltage Readings

Peak-Peak: 28 mV

Peak of Wave: 880 mV

Trough of Wave: 856 mV

AC Voltage Readings

Peak-Peak: 28 mV

Peak of Wave: 12 mV

Trough of Wave: -16 mV

 

Zener Diode Circuit (Correct)

 

 

Oscilloscope Reading of Zener Diode Circuit (Correct)

 

 

 

 

Correct Orientation

DC Voltage Readings

Peak-Peak: 60 mV

Median of Wave: 12.4 V

AC Voltage Readings

Peak-Peak: 60 mV

Median of Wave: -20 mV

The addition of the zener diode went even further towards resolving the original two AC waveforms into a single waveform that displays a very DC like nature. When the zener diode was incorrectly it decreased the overall voltage of the waveform and did not do as good of a job at smoothing out the waveform, and visually it appeared to increase the noise. When the zener diode was oriented correctly the waveform was almost completely smoothed out, as the peak-peak voltage was decreased to 60 mV.

VI. Light Emitting Diode

For this part of the experiment an indicator consisting of one 430 Ω resistor, one 1 kΩ resistor, two 1N4002 diodes, one 100 μF electrolytic capacitor, one 1N5242B zener diode, and one LN21RPHL LED  was constructed on the Heathkit.

Both the diagram and actual setup can be seen below.

LED Circuit w/ 1 kΩ resistor

DC Voltage Readings w/ 1 kΩ resistor

Peak-Peak: 40 mV

Median of Wave: 12.1 V

Current: 11.92 mA

Current from resistor to led: 9.86 mA

These readings made sense as they are very close to the theoretical value that you can determine by using the equation I = V/R

I = 12.1V/1kΩ= 12.1 mA

The measured value of 11.92 mA is off by only 1.5%.

LED Circuit w/ 5.1 kΩ resistor

VoltageReadings w/ 5.1 kΩ resistor

Peak-Peak: 40 mV

Median of Wave: 12.3 V

Current across led: 2.401 mA

Current from resistor to led: 2.030 mA

These readings made sense as they are very close to the theoretical value that you can determine by using the equation I = V/R.

I = 12.1V/5.1kΩ= 2.37 mA

The measured value of 2.401 mA is off by only 1.3%.

This shows the difference that a change in the resistor makes in a quantitative manner. If you increase the resistance of the resistor than the current that flows across the resistor and then to the LED is decreased proportionately. Qualitatively, this is also apparent because when the 1 kΩ resistor was replaced with the 5.1kΩ, the brightness of the LED dimmed.

In this section I quickly realized that the current configuration of my circuit was bunched too closely together to add the LED. I switched up the wiring and after some initial confusion I was able to configure it in a way that worked. I had hoped to try out a wider array of resistors in this circuit but as class time was quickly dissipating I instead needed to dismantle the circuit and move on to the full wave bridge.

VII. Full Wave Bridge

For this part of the experiment a full wave bridge consisting of one 430 Ω resistor, one 1 kΩ resistor, four 1N4002 diodes, and one 100 μF electrolytic capacitor was constructed on the Heathkit.

Both the diagram and actual setup can be seen below.

 

 

Full Wave Bridge Circuit


Oscilloscope Reading of Full Wave Bridge

DC_Voltage Readings

Peak-Peak: 1.80 V

Peak of Wave: 14.6 V

Trough of Wave: 12.6 V

AC Voltage Readings

Peak-Peak: 1.80 V

Peak of Wave:1.20 V

Trough of Wave: -600 mV

 

The full wave bridge configuration is supposed to mimic the output of the filtered full wave rectification circuit, but without the input of two different wave forms. The jagged tooth nature of the full bridge waveform is similar to that of the full wave rectification, but the former appears smoother than the latter. In the both the bridge setup and the original filtered setup the mean voltage was 13.6, but the peak-peak voltage was greater in the bridge (1.80 V) than that of the original filtered (720 mV).

I was initially confused because it did not appear to look like the full wave rectification circuit, but after talking with Anthony I realized that this was the case because the original full wave circuit did not include the filtering effects of the capacitor.

During the lab there were many other students that had bizarre outputs on their oscilloscope displays for the full bridge setup. Additionally, Dr. Koch presented the reasons for these issues in an email sent out to the class. I am unsure why I did not encounter this problem.

Final Observations

This lab was filled with challenges that were not readily apparent from the fairly straightforward presentation of the instructions and these were further exacerbated by my not double checking to see if I had all the correct equipment. To prevent this from taking place again, with regard to resistors, I have downloaded the resistor identification app for my android tablet. I also learned on the second day that I, along with others in the lab, had grabbed the incorrect zener diode. This accounts for the fact that I was able to melt the supposed zener diode on the first day of lab when I should have not been able to. I also, need to check the configurations on my tablet as the photos I took with  it were much smaller than those I took with my Iphone, which led to some of the oscilloscope displays to  be more difficult to read.

In regard to safety I learned that it is probably a good idea to turn off the Heathkit while setting up or altering the circuit. This helps to prevent one’s self from getting burned from over heated diodes.

 

Details of Materials

USB-1208LS USB-based Analog and Digital I/O Module (Board Serial #163)

Heathkit ET-1000 Circuit Design Trainer

Tektronix P2220 Voltage Probe

Tektronix TDS 1002 Two Channel Digital Storage Oscilloscope

Acknowledgements

Dr. Koch

Anthony Salvagno

Panitz PDF on Diodes and Rectification