Put power supply on stripboard or learn "Eagle" software?

Thread Starter

darrough

Joined Jan 18, 2015
86
I am going to construct a regulated DC power supply to provide a low-ripple adjustable dual-output voltage in the range 5-12 VDC at 0.2 Amps (maximum) load current from a 120 VAC power outlet.

http://my.ece.ucsb.edu/York/Bobsclass/2B/Labs/Lab 2 - 2B 2010.pdf

Unfortunately, the professor did not provide a layout for the PCB. (It seems that students obtain the PCB from the lab assistant).

What issues would I run into if I did this project on strip board?

I understand that there is software, called "Eagle", that can create a PCB from the schematic. Does this software do everything automatically, or is a great deal of knowledge needed to use it? Would I be better off to create my own PCB layout and then send it to a PCB batch service?
 

#12

Joined Nov 30, 2010
18,223
Whether you learn Eagle or do the layout yourself is a rather personal decision. As an old fart, I find this kind of project to be child's play and do it on a piece of 10 line per inch graph paper. That way, the sizes match up with my 10 hole per inch perfboard.
 

tracecom

Joined Apr 16, 2010
3,944
I am going to construct a regulated DC power supply to provide a low-ripple adjustable dual-output voltage in the range 5-12 VDC at 0.2 Amps (maximum) load current from a 120 VAC power outlet.

http://my.ece.ucsb.edu/York/Bobsclass/2B/Labs/Lab 2 - 2B 2010.pdf

Unfortunately, the professor did not provide a layout for the PCB. (It seems that students obtain the PCB from the lab assistant).

What issues would I run into if I did this project on strip board?

I understand that there is software, called "Eagle", that can create a PCB from the schematic. Does this software do everything automatically, or is a great deal of knowledge needed to use it? Would I be better off to create my own PCB layout and then send it to a PCB batch service?
There is no reason you can't use stripboard, but there's also no reason you can't use perfboard or point to point wiring (or a combination thereof). The learning curve for Eagle or some other full-featured schematic capture/PCB layout software is too steep to justify learning it for a single project like this one. However, an easier alternative is PCB Express, if you really want a printed circuit board.
 

MrChips

Joined Oct 2, 2009
25,040
Tell Bob York that he has made some serious errors with his diagrams and wiring to AC mains.

Page 1, Figure 2-1, photo clearly shows the AC switch and fuse in the wrong locations.

Page 7, Figure 2-8, schematic shows AC switch and fuse in wrong locations.

Page 8, Figure 2-10, (a) and (b), switch and fuse in the wrong locations.

Here is the correct way to wire the fuse and switch to AC mains.

AC Live (BLACK) - fuse - switch - transformer - AC Neutral (WHITE) (for North America colors).

The fuse must come before the switch. Both fuse and switch must be on the LIVE (Hot) AC mains. Never on the neutral side.
 

ErnieM

Joined Apr 24, 2011
8,218
I would skip the PCB and hand wire this point to point.

The issues MrChips raises are real and serious. You want the switch and the fuse to kill the hot AC line as it enters the device.

I don't like the type of fuse holder used as there is no way to keep it "finger safe" when replacing the fuse!

Assuming you are not taking this course and building this on your own do make those changes. If you are in the course do tell Bob.
 

crutschow

Joined Mar 14, 2008
28,545
I noticed another minor error in the design. It has a 470Ω resistor for R1 but its maximum value should be 120Ω according to the data sheet. This is to insure that there is a path for the minimum output current under no load.
For that you would also need to reduce the value of the pot R2. The nearest standard value would be 1kΩ. To keep the ratios about the same, use a value of 100Ω nominal for R1.

One significant problem I see is that the rectifier output voltage won't be enough to provide a 12V output from the regulator.
The 9Vac transformer output will provide a rectified output of about 12V DC.
Since the LM317 requires at least a 2V drop across it for proper operation, then its maximum output will be less than 10V under load.
Don't see how they claim a 12V output. :confused:
 

SgtWookie

Joined Jul 17, 2007
22,221
There's another problem with the original schematic; EARTH is not connected to anything. It should be connected to the transformer's secondary side ground (the center tap), as otherwise if the transformer shorts to the secondary winding, the fuse won't blow, and the person using the supply could be electrocuted.
 

tracecom

Joined Apr 16, 2010
3,944
He's a prof at UCSB and his contact info is easy to find if anyone wants to contact him. My advice to the OP (if he is a student, and isn't long gone) is to keep mum until the grades are posted at the end of the term.
 

Thread Starter

darrough

Joined Jan 18, 2015
86
You say that the fuse goes on the "hot" side. Which side is that?

The instructions say to attach the ground line to the case of the transformer. The schematic shows 3 earth grounds. Do these also go to the case of the transformer?

Does wire connecting the plug to the transformer to the switch to the fuse all have to be the same gauge? If not, what what gauge would be safe for the switch? It will be about 6 inches long.
 

#12

Joined Nov 30, 2010
18,223
You say that the fuse goes on the "hot" side. Which side is that?

The instructions say to attach the ground line to the case of the transformer. The schematic shows 3 earth grounds. Do these also go to the case of the transformer?

Does wire connecting the plug to the transformer to the switch to the fuse all have to be the same gauge? If not, what what gauge would be safe for the switch? It will be about 6 inches long.
1) The, "hot" side of the power line is the side that has 120 volts AC on it, compared to ground and neutral. It is also the smaller vertical slot in the wall outlet.
2) The whole purpose of using one symbol at several places is to tell you that those places are connected together.
3) You are making a 5 watt power supply. That requires less than 0.1 amps from the power line. Mathematically, you can do that with size 30 AWG copper wire, but it will break a lot when you handle it. Best to just use the same size as the power cord. Somewhere around 18 Ga.
 
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