Rejected!

Hey guys. A lot has happened since my last post. This one will specifically talk about the experience about creating our regulated power supply (Because I forgot some of the things that occurred so, blame my memory). So it has been two weeks. Two weeks that we didn't have class for ECE 136. The instructor discussed a regulated and an unregulated power supply before giving us the instructions of computing, designing, and building our own power supply. We had to gather and compile all our knowledge of electronics to analyze and compute for the resistance values. 

Schematic Diagram of the Split Power Supply
Note: The values in the diagram are different
from the values computed. However,
the same transistors and rectifier diodes were used.

Yesterday was the last meeting and the scheduled checking for the said power supply, where, unfortunately, most of us, if not all, got rejected. Sad. We stayed up all Sunday preparing for it. 

It got rejected because of the 'poor' or 'technician' quality of the work: the component layout, the specific measurement of the placement of components, and the soldering. I feel very sad for Duaine, though. He was still soldering when the instructor came to the laboratory. He inspected his work, and commented that the capacitor overlapped with the diode, and said,  "I reject this" or something similar. He did praise him for his foil design and soldering abilities afterwards, but it was still rejected. 

Circuit Design Progress. 

He gave us specs about the placement and spaces before, but I guess you forget them when you're working in limited time. I personally measured mine, both in the first and the second etching, but I had a jumper in the foil because one foil accidentally chipped off. Maybe because of the high wattage of the soldering iron I was using. I re-etched because the foil of my first board was already peeling off, again because of the soldering iron and because of the constant changing and replacing of transistors. That was Sunday evening. 

On Sunday, most, if not all of our circuits were already performing well, unloaded. The circuit's output was more or less ± 15. But when a load resistance is applied, the voltage drop is huge, therefore we had to adjust our components accordingly. And we had to troubleshoot our circuit if it's not within that range. 

My circuit's output in the positive side, (by the way, the power supply is a split power supply. so it has three outputs, a + output, a 0 or ground, and a - output) is already working perfectly. With a more or less 90% ratio. My negative side, however, was a disaster. The unloaded output was -15.4V, when a load resistance is applied, it goes down to -1.98V. Another reason for me to re-etch my original circuit. We spent so much money changing transistors, which is the 2nd most expensive component beside the capacitor. Everyone else's loaded output is more or less 13V. Thankfully, I was able to find the problem Monday morning. It was the foil design! The base of one of the transistors was connected to a track which was not supposed to. I just had to cut that connection with a cutter. After that, my negative output was about -12V which is better than -1.98V. 

Meanwhile, the others was so frenetic about the ratio of their loaded and unloaded that they accidentally damaged their circuit. Sometimes the output went to 17V and loaded to 3V. I just settled with my 82% and 89%.

I forgot to mention that the specs for the power supply was:  15V 250mA. Which will be used to power a tone control and a pre-amp.

For the first week of no classes (SCUAA week), we began working with the case for the power supply and the rest of the tone control. The case was composed of a 3" counter trim for the frame, angles bars are attached to each corner to ensure sturdiness, and a sheet of metal for the base. I like getting my hands dirty, so this was a fun build. And it's even more enjoyable if your working with friends.


All was going well, until we unwrapped a roll of metal sheet. I was out of my mind. It all went very fast. The roll just went finger ninja and sliced my thumb, just below the nail. I was lucky to have my friends there. I could've blacked out if it weren't for them. They rushed me to the hospital to get treated. I was thankful I didn't lose a thumb! Whew!

http://instagram.com/p/wiRD_JDHTq/

EDIT:
20 DEC 2014
Yesterday I re-etched, again, this time, using a custom PCB component in PCB Wizard [link] that I created. I used mspaint to fill in the remaining parts of the board because PCB wizard can't add copper shapes to some pads. (It has this gap thingy) This is now the version 4 of the ckt.

Version 4 of the Split Power Supply. Converted all the resistors
and diodes. adjusted the terminal length of the small caps.

As of writing, I still haven't tested the new circuit (with old parts!) because of the zener diodes. In the first design, the terminal distance was 7.6mm. I changed it to 11mm, now, the leads aren't long enough to make it to the solder side of the board.

And I am currently building an "In Circuit Transistor Tester" from the book Projects and Circuits Volime 1. So far I have bought the components, and re-designed the pcb design. But the iron is broken so I can't transfer the toner. I think I will do a tutorial on Toner Transfer Method and the other methods, and another post about the in circuit transistor tester. Till then, Cheers!

PS: I will add more photos soon.