• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Resource icon

ULTRA clean 9VDC Power Supply Project 2010-07-09

Here is a small power supply project that I would like to share with all the members of this forum.

PLEASE SEE BOTTOM OF PAGE FOR FINAL PROJECT PICTURES

The project is centered on the LM317T regulation chip:

http://www.national.com/pf/LM/LM317.html

NOTE: The supply can be configured to any voltage between 1.2 to 37V.

My reason for building this circuit: In need of a QUIET 9V power supply to power 3 guitar pedals.

Each pedal is rated @ 250mA making a total load of .75A.

The LM317t is rated at 1.5A w/ heat sink - making it an ideal choice!

Please refer to the picture 1-13 as they are called: PIC #xx:

Ok, Lets get started! :)

NOTE: Please understand that I have only been practicing electronics for only one year and may do things that other, more knowledgeable, members may see as wrong. This project is for anyone – I have tried my best to make it as simple as possible.

Please be SAFE!

Pic#1: Here is the project schematic we will be referencing to

Tools needed:

-A ruler, pencil and paper
-A black sharpie marker
-Hammer
-A small punch
-A drill or DRILL PRESS
-A set of metal drill bits 5/64 - 1/2"
-A ziplock baggy or plastic dish
-A Soldering iron < 35W

PIC #2: Special Supplies

-Ferric Chloride Etchant
-Isopropanol (Rubbing Alcohol)
- (1) 2 1/2" X 4" blank copper clad board
-Iron Wool

PIC#3 Components

Component List:
Resistors (1/4 watt rating)
1 - 270
2 - 2k
1 - 6k8

Capacitors (minimum rating 35 volts)
2 - 0.1uF
1 - 10uF
1 - 470uF
1 - 1000uF

Regulator (As requested by Hero)
1 - LM317

Other
1 - 120vac/12.6vac step down transformer

http://www.radioshack.com/product/index.jsp?productId=2102702&cp=2032058.2032230.2032277&parentPage=family

1 - power cord
1 - on/off switch (optional) SPST rated at 3A or higher
1 - Transistor socket (optional)
1 - Full Wave 4A Bridge Rectifier
2 - 1N4002 diodes
1 - Heat sink for the LM317
3 - coax power jacks
22 gauge stranded wire
Metal Enclosure

Ok, so we've got all of our materials... lets begin!

Printed Circuit Board Planning:

I feel planning is one of the most important processes to consider when creating a circuit.. no matter how simple it may be.

Using the schematic, visualize what the circuit will look like on the PCB. (Printed Circuit Board) Take into account the SIZE of every component especially larger components such as heat sinks and capacitors.

Make a few rough drafts of the layout you want for the circuit.

Something’s to consider:

-Since the GND of most circuits is the most heavily populated - Border the PCB with the GND track.

-Always draw to exact scale... even in the rough draft

-Use the actual components when making the spacing on paper

Ok, so we have our rough PCB design completed!

PIC# 4 My Rough PCB Design Draft

Transferring the rough design to the blank copper-clad board:

First we MUST clean the board..

Using the Iron Wool, scour each side of the board.. making the surface rough.
(30 seconds per side)

Next, using an all-purpose cleaner - such as comet - lather and rinse the board to ensure it is free of dust and grease.

The purpose of cleaning the board is to ensure good contact between the ink of the anti-etchant sharpie marker and the copper of the board.

Now we are going to actually hand draw our rough draft on to the copper board...

If this is your first time attempting this I highly recommend you make your tracks as wide as possible to unsure no line breaks when etching (As you can see in MINE)

Also, as pointed out by other members, you can use other, more costly, methods to transfer the design to the PCB.

PIC# 5: Here is my board with the ink design.

Now then! We can etch the board :eek:

Be warned this can get VERY messy and you will most likely loath Ferric Chloride afterwards.

PIC# 6 My preferred etching setup.

My method: I place the designed and soon to be PCB into a ziplock bag. Then, using a hook I attach the bag to the wall and add approximately 200ml of Ferric Chloride. I then use tape to add pressure to the bag raising the Ferric Chloride over the highest point of the board.

The reason I like to do this vertically is because - FOR ME - it is faster. It is faster because the copper sediment falls downwards once dissolved (Compared to horizontal laying in a tray). Please do this which ever way you prefer!

PIC# 7: Here is my etched board

You will now see that the black marker ink is still over the copper, don't worry that is a good thing!

You will now need to use a small amount of rubbing alcohol to.. well RUB off the ink!

PIC# 8: My cleaned board

PIC# 9: Punch and Drill

Now it is time to punch and drill the board. Punching is not required but it does make the drilling process MUCH easier, especially if you do not own a DRILL PRESS. Using your rough draft, punch the necessary holes.

PIC# 10: Drill Press

Using a 5/64" drill bit, drill each hole you have punched.

Once you have drilled the holes you will notice that the exit hole of the drill bit has caused the plastic to protrude out. This can be smoothed out by taking a larger drill bit (I use a 1/4" bit) with your hand and simply turning the head of the bit over the protruding surface. The excess plastic will fall right off if done correctly.

This is called deburring, thanks HERO.

The PCB is now completely etched, drilled and ready to go... but first...

Using my rough draft and a pencil, I like to label where each component goes on the PCB. These label go on the top side.. WHICH IS NOW THE SIDE WHICH HAS NO COPPER.. I say the side with no copper is the top because this is where the components will be sticking out. I use labels to decrease confusion since the PCB is now reversed (when looking at it from the top)

PIC# 11: Here is my labeled PCB ready to be populated with components.

Now for the best part! Populating the board!

Gotta love the smell of solder :D

When soldering I make the connections in this order:

1) Resistors (Since they are smallest)
2) Diodes (same reason)
3) Bridge Rectifier
4) LED wires
6) Capacitors (Since they are so large and raise the board)
7) LM317T (Transistors, ICs and regulators are not heat friendly! When soldering these always make the solders FAST and wait at least 20 seconds between solders! Use a heat sink if part is expensive)
8)Transformer leads
9) Using wire nuts attach a power cord to the PRIMARY 120VAC leads of the transformer.

PIC# 12: Here is my populated board w/ LED and Transformer

Before plugging the unit in for the first time:

-120VAC is EXTREMELY dangerous! Make sure, at all times, you know where the wire nuts between the mains and the transformer are!

-The wire nuts are for test purposes ONLY!

-When I make the circuit pretty and assembly it into the metal enclosure I will be using shrink-wrap to ensure the transformer connections are safe!

-I will also be using a grounded cord, OF COURSE.

PIC# 13: Here is the power supply plugged in. The LED indicates the circuit is working. The voltage read out is 9.34V.. exactly as planned! The heat sink is also seen in this picture (Big Black Thing)

- You will see that I have added a fuse on my board. This is not required because the LM317t is thermally protected.

- LED ADDITION: I have added an ON/OFF green LED indicator which is not on the schematic provided. Simply add a 1000:eek:hm: resistor on the PCB for current limiting then use 22 gauge stranded wire to connect the LED.


Thanks for reading through my project and I hope you try it out!

What’s next?

From here you can either add the coax DC jacks in the 3 open +9 and GND spaces and use the supply.

OR

place the circuit into a metal box and then add the coax Jacks

I will finish this project later this week by assembling it into a metal case and making it pretty and such. I will update the thread when I am finished the project.


Constructive feedback is always welcome.. no matter how MEAN it may be :D (as you can see by Hero's feedback :D)

Peter W
March 25, 2007
Author
Peter_wadley
Views
39
First release
Last update
Rating
0.00 star(s) 0 ratings

Latest threads

EE World Online Articles

Loading

 
Top