Breadboard Power Supply

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Breadboard Power Supply

Postby DrNomis » 15 Oct 2010, 10:30

Hey Everyone,these are a couple of pics of a Breadboard Power Supply which I designed myself,it is easy to build,and has positive and negative supply outputs which can be independantly varied from about 1.7 Volts to 19 Volts,and can supply a maximum of 500mA..... :)

I was wondering if there would be any interest in making this a constructional project for all members of Freestompboxes.org,I can supply all constructional details of my Breadboard Power Supply...... :)
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Re: Breadboard Power Supply

Postby IvIark » 15 Oct 2010, 10:44

Yes I'd be interested in something like this. At the moment I just use a battery snap to the power rails so something like this would be a good alternative.
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Re: Breadboard Power Supply

Postby DrNomis » 15 Oct 2010, 10:54

Cool Iviark,


There is some mains wiring involved in the construction of this power supply,do you have a friend who is competent in mains wiring?


I'll be drawing up the schematic for this and uploading a pic of it this weekend,so stay tuned.... :)
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Re: Breadboard Power Supply

Postby IvIark » 15 Oct 2010, 11:42

DrNomis wrote:There is some mains wiring involved in the construction of this power supply,do you have a friend who is competent in mains wiring?

:secret: I was an engineer at Siemens for 14 years, so I've got that one covered!
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Re: Breadboard Power Supply

Postby DrNomis » 15 Oct 2010, 11:45

No worries then Iviark.... :)
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Re: Breadboard Power Supply

Postby DrNomis » 15 Oct 2010, 11:47

Okay,just give me a few minutes and I'll draw up the schematic of the power supply and post it here for you Iviark.... :)
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Re: Breadboard Power Supply

Postby DrNomis » 15 Oct 2010, 12:27

And here it is,the Schematic of my Breadboard Power Supply,feel free to build this for your own use.... :)


Brought to you in the True Spirit of Freestompboxes.org..... :)




You may be able to suggest any improvements,and,or refinements.... :)
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Re: Breadboard Power Supply

Postby IvIark » 15 Oct 2010, 12:47

Cheers Simon, I'll check it out
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Re: Breadboard Power Supply

Postby DrNomis » 15 Oct 2010, 12:52

No worries at all mate..... :)
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Re: Breadboard Power Supply

Postby DrNomis » 15 Oct 2010, 17:24

Oh,i just realized that I didn't include the specs for the mains fuse that is after the power switch,it is a 1A 250Vac type,I know,probably a bit overated for the job..... :)
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Re: Breadboard Power Supply

Postby DrNomis » 16 Oct 2010, 02:41

The Datasheets for the LM317T,and LM337T Adjustable Voltage regulators,specify a maximum current output for these devicces of 1.5A,but,using a 2N3055 and an MJE2955,you can boost the output current capability up to 3 Amperes,or up to something like a massive 10 Amps.... :)
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Re: Breadboard Power Supply

Postby DrNomis » 18 Oct 2010, 07:59

Just thought I would do a quick update..... :)



If anyone is planning on building this design for themselves,make sure that the primary winding of the power transformer you use is rated for the mains voltage in your part of the world,the mains voltage supplied to your wall socket is not the same for all parts of the world,I live in Australia and the mains voltage is 240Vac @ 50Hz..... :)


The mains voltage in America is something like 110 or 120 VAC @ 60Hz.... :)


England,I think is 230 VAC @ 50Hz.... :)


Europe,I think is 220 VAC @ 50Hz or it could be 60Hz..... :)


The secondary voltage rating of the power transformer for this power supply can be a centre tapped 15VAC-0V-15VAC @ 500mA,or anything up to 1A.


I used a couple of small heatsinks bolted directly onto the metal tab of each regulator,in operation,the two regulators should not get very hot unless alot of current is being drawn from the supply.... :)


Note,be very careful when doing the mains wiring,get someone to double check that all mains wiring has been done correctly,because there is very little room for error,one error could result in a danger of electrocution,so please be careful.... :)


Use heatshrink tubing to cover any solder connections that may have mains voltages on them,particularly those on the power switch and mains fuse holder.... :)
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Re: Breadboard Power Supply

Postby CRBMoA » 19 Oct 2010, 23:39

Pardon me for being dense.

I built a similar device 20 years ago, and use it to this day.

It is variable from about 3.0V to 36V DC. But when I hook a load to it, since there is no voltage regulation, I experience a voltage drop. Nominal, but it exists.

Is there a way around this, or is it the nature of the beast?
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Re: Breadboard Power Supply

Postby DrNomis » 20 Oct 2010, 04:44

CRBMoA wrote:Pardon me for being dense.

I built a similar device 20 years ago, and use it to this day.

It is variable from about 3.0V to 36V DC. But when I hook a load to it, since there is no voltage regulation, I experience a voltage drop. Nominal, but it exists.

Is there a way around this, or is it the nature of the beast?





If you could post a schematic,I could probably work out what's causing the voltage drop.... :)


This design of mine uses two 3-terminal adjustable voltage regulators,normaly,a small trimpot is used to set the output voltage,but I used a standard 24mm 5kLinear pot instead of a trimpot,I wanted to design an easy to build power supply for my breadboards and be able to set the positive and negative volts to wherever I wanted it... :)


Hmmmm...it could be that when you hook a load up to your power supply,it has trouble supplying enough current,what is the current rating of your transformer?..... :)


The best way around the issue you are having with your power supply,that I can think of,is probably to improve the regulation of it,or if you want,feel free to build a power supply from my design,for yourself.... :)


All values of components are exactly what I used in my build..... :)
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Re: Breadboard Power Supply

Postby Greg » 21 Oct 2010, 03:21

DrNomis wrote:
....I live in Australia and the mains voltage is 240Vac @ 50Hz..... :)


The mains voltage in America is something like 110 or 120 VAC @ 60Hz.... :)


England,I think is 230 VAC @ 50Hz.... :)


Europe,I think is 220 VAC @ 50Hz or it could be 60Hz..... :)



Since 2000, Australia is actually "officially" 230 V 50 Hz.. same as UK and most of Europe.

Nothing has really changed, as 240 V still comes within the tolerance of +10% -6%, but we're officially the same as Europe and any device meant for there is good for use in Australia... after a plug change.
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Re: Breadboard Power Supply

Postby DrNomis » 21 Oct 2010, 06:05

Thanks for that Greg_G,cheers mate... :)
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Re: Breadboard Power Supply

Postby jstbrowsin » 17 Jan 2011, 04:02

Hi guys,

last year at tech we built something similar to Dr Nomis supply however I fear it was a bad design because after about 4 hours of use (using a range of 9V - 18V depending on what I am working on at the time) it blows the caps and sometimes even the transistors. :slap: Damn awful smell (go on you know :lol: ) and a bloody loud bang! :shock:
If possible could one of you kind people look over this schem for me and tell me what I need to change to make this a more reliable supply please?
Any help would be gratefully appreciated thanks.
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Re: Breadboard Power Supply

Postby PokeyPete » 17 Jan 2011, 13:24

jstbrowsin wrote:Hi guys,

last year at tech we built something similar to Dr Nomis supply however I fear it was a bad design because after about 4 hours of use (using a range of 9V - 18V depending on what I am working on at the time) it blows the caps and sometimes even the transistors. :slap: Damn awful smell (go on you know :lol: ) and a bloody loud bang! :shock:
If possible could one of you kind people look over this schem for me and tell me what I need to change to make this a more reliable supply please?
Any help would be gratefully appreciated thanks.

The way DrNomis built his power supply is practically right out of a National Semiconductor Linear Data Book. It is a typical
way to build a variable +/- supply. Your version is a little different. You don't really have a +/- supply. You have two
semi independant power suppies. The - and + indicators on the bottom supply are inaccurate. They should be identical to the
one above it. You have two 1.25V to 26V positive suppies. You can jumper the true + of the bottom supply to the - of the
upper supply and have a variable supply of up to about 52V. Or, jumper them the same way and use that as ground for a +/-
supply. You didn't state which way the LM317(s) were packaged.....T or K. But, either way, at the current levels possible on
this supply, they will need a great deal of heatsinking. My guess heat is killing your supply. Inadequate heat sinking is probably
the culprit.
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Re: Breadboard Power Supply

Postby DrNomis » 17 Jan 2011, 17:24

Yeah,I can see what's happening in the schematic,basically the two supplies are identical,that is,they are both positive supplies,one of them is labeled with incorrect polarity indicators,one has the negative terminal where the positive terminal should be,I think the supply would work much better if an LM317T AND an LM337T are used instead of two LM317T regulators,I have had my Power Supply running for much longer than 4 hours and it did not blow any capacitors or semiconductors,and still continues to work fine.... :)


I also noticed that,if the two outputs ate connected to obtain positive and negative supplies,the ground connection will be floating..... :)


The circuits I used for the design came from a Jaycar Electronics Catalogue,I included a heatsink for both regulators,and I have had no issues whatsoever with overheating,even though the heatsinks are in a closed case with no ventilation holes (I might sort that out soon).... :)


Also,you have FC1 and FC2 as 4000uF capacitors,but no "Working-Voltage" specified for them,I'm assuming that they are most likely 50V Caps,if they aren't,I would suggest using 50V Caps or maybe 65V Caps for them..... :)


If anyone wants to use my power supply design,feel free to do so,since the design uses standard building blocks and design practices,and can't be copyrighted.... :)
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Re: Breadboard Power Supply

Postby jstbrowsin » 18 Jan 2011, 00:25

Thanks Pokey Pete and Dr Nomis for your input. Most appreciated.
I guess I should have been more specific with my info, the caps that blow are the C1 & C2 and they are rated at 63V, in turn they also blow the 2N3055 T03 transistors that have a huge heatsink. The LM317's are T package and there are no heat sink's attached :oops: but I can remedy this 8) . The filter caps are rated at 75V so I think they should be safe too eh.

Ok so going on your advice I change the LM317T in the neg supply to LM337T and add heat sinks.
Would it also be advisable to double the size of resistance (R1-R2) to slow the current and save the transistors and everything else?

[quote="DrNomis"]
I also noticed that,if the two outputs ate connected to obtain positive and negative supplies,the ground connection will be floating..... :)


Pray do tell how can I remedy this please?



Thanks again for all you help guys :)
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