This week the team met throughout the week to expedite the completion of the AC-DC power supply, DER / Success Criteria documents, and will also begin formatting all of our tests and completed work to begin chapter 3 of our report, to help maintain steady progress. The first lesson learned data, discovered during the east campus test, was also updated to the website.
Team
After our meeting with the professor, the team met at the East Campus on Thursday night 1/24, to test trial our design for the AC-DC power supply.
After building and testing the circuit on a breadboard, the desired outputs were achieved, and the final design can now be soldered to a PCB. Once the circuit is soldered to the PCB, further bench tests will be conducted for each output of the power supply, on Tuesday 2/1 at the West Campus.
Pictures of the teams breadboard tests conducted Thursday night at the East Campus are shown below:
Close up of the breadboard used for testing.
Oscilloscope measurements to test the power supply for each output are shown below.
12V 3.3V
+5V -5V
Hunter
This week began by conducting Pspice simulations for testing the voltage regulators that will be used for the power supply. The schematic below was used to build the circuit on a breadboard for bench-testing trials at the East Campus.
Pspice Schematic for the AC-DC power supply's voltage regulators:
Pspice Simulation for the AC-DC power supply's voltage regulators (above) and relative values (below) :
Regulator Data-sheet Information:
LM237_ADJ, used for -5V:
[1]
LM317_ADJ, used for 3.3V:
The original schematic from last weeks progress log could not be used for the 3.3V regulator. This is due to the line regulation parameter, which needed a little more power than the series configuration that was initially simulated. This is the reason for the updated schematic for this week. The LM317_ADJ regulator, for the 3.3V output, is now in parallel with the 12V regulator, with respect to the output of the 24V power supply.
The picture below shows the line regulation that was overlooked on the first schematic that was simulated last week, which did not provide enough voltage for stable operation. [2]
LM317_ADJ, schematic for 3.3Vout:
TL780_12V
The configuration for the 12V and 5V regulators are similar, with the only difference being that with the 12V regulator it is recommended to have C2 = 0.22μF, where the 5V regulator (shown in next figure) recommendation to have C2 = 0.1μF. [3]
uA7805_5V:
Similar to the 12V regulator, C2 = 0.1μF, otherwise for a fixed output their circuit design is the same. [4]
For all the regulators, except the -5V regulator, diodes are applied in two locations for additional circuit protection, as the next two figures from the datasheet display below:
The "weekly minutes with professor" page was also updated this week:
References:
[1] Texas Instruments, “LM237 3-Terminal Adjustable Regulator,” LM237_-5V datasheet, SLVS047L, November 1981 [Revised January 2015].
[2] Texas Instruments, “LM317 3-Terminal Adjustable Regulator,” LM317 datasheet, SLVS044Y, September 1997 [Revised April 2020].
[3] Texas Instruments, “TL780 Series Positive-Voltage Regulators,” TL780-12 datasheet, SLVS5055M, April 1981 [Revised October 2006].
[4] Texas Instruments, “uA7800 Series Fixed Positive Voltage Regulators,” uA7805 datasheet, SLVS056O, May 1976 [Revised August 2012].
John
After initial breadboarding of the AC-DC power supply was completed, John worked on soldering a more permanent prototype to be used in the Bench-Test trials on Tuesday 2/1.
Here is the supply with all of the positive regulators terminated. Notice the LM317 (left) is backwards relative to the other regulators. This was done to compensate for the "backwards" pin placement of the LM317 package. Notice also the 4 Header pins (right) that will allow the board to be mounted directly to a breadboard for testing.
This leads are looped over to the top of the board and will allow for easy attachment of the scope probe to measure the +5V(left) and +12V(right) supply outputs.
Here is a top view of the finished proto board attached to a breadboard. The LM237 is mounted differently, again to compensate for its unique pins. Protection diodes (1n4001) and filter electrolytics are all rated for 50V. Resistors are 1/2 watt, 1% metal film.
This loop is the -5V measurement point.
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