First power supply

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#1
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Hi, I really need a power supply to output about 0~15v, with about 1 or 2 amps of current. Does anyone have any suggestions for a decent bit of gear. I'd rather steer clear of Chinese knock-offs, but I am aware that they are really the only option in my budget (<£50). BTW, old eBay gear isn't really a possibility for me, since most of it is from the USA, and I live in the UK. Where is the best place to get it, new from eBay, Amazon or elsewhere. It could also be helpful to know that that I have nothing in this field: I've been trying out logic blocks, and I'm using my arduino uno as a power source, which is a bit of a pain. 

Thanks,

Ben

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When I was young, I built one from junk parts. Transformer, diodes for bridge, filter capacitors, 2n3055 power transistor, heat sink, wire wound potentiometer, a few resistors and zener diode. A zener and resistor were used for a reference voltage, then the potentiometer divided the voltage for adjustment, to feed the base of an emitter follower circuit, using the power transistor. It had some load drop, but it worked for me, from the mid 60's to mid 70's.

It all starts with a mental vision.

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That is interesting... I guess that is basically the guts of an LM317. Could you expand on the zener voltage reference please. Is it also practical to include a simple voltage divider on the output to create a +ve and  -ve supply? Cheers,

Ben

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Hmmmmm, package not sealed yet..........

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

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Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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A notebook power block, usually around 19V 3.5A, an LM317 on heatsink and a pot and you're close to your first PSU.

A GIF is worth a thousend words   They are called Rosa, Sylvia and Tessa, You can find them https://www.linuxmint.com/

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I am sure you can find how to use a zener as a shunt regulator, and how to use transistor as emitter follower.

Your idea of LM317 is great. Do that. Or use the high speed PWM, of a tiny AVR to make a buck regulator.

If you need a bipolar supply, make two. With PWM and ADC, close the loop and regulate.

It all starts with a mental vision.

Last Edited: Sat. Jan 3, 2015 - 10:47 PM
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I have a pair of these http://www.maplin.co.uk/p/100w-slim-bench-power-supply-n93cx

 

Bit more than your budget but I can recommend them - you can set max output current required as well as the voltage

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The notebook supply and LM317 is a good solution, as it already includes some current limiting. However you don't get a +-supply this way.

Its easy to add fixed voltages like 5 V and 12 V.

 

Using a µC to do switched mode voltage regulation is a rather tricky method and a regulation of a LM317 is far superior.

I don't know about the UK, but there should be some source for electronic components as well - they often also sell supplies. 
 

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 Thanks, I've been trying to get my head around zener references, and I'm now pretty confident with the emitter follower set up, but perhaps I should go with the available LM317 for this first project. What do you guys think? 

Ben

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Also, can I split Vout with a resistor divider, tapping the centre and buffering it with an open loop configured op amp, which will become the ground of the circuit? Won't this give me a +ve and -ve supply?

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Kleinstein wrote:
The notebook supply and LM317 is a good solution, as it already includes some current limiting.

Yes. And it also gives you all the safety protection!

 

Quote:
However you don't get a +-supply this way.

True - but how often will you actually need that?

 

For new bench power supplies, see: http://www.rapidonline.com/Elect... - there's a few in there under fifty quid...

 

There seem to be a few on ebay at the moment:

 

http://www.ebay.co.uk/sch/i.html...

 

http://www.ebay.co.uk/sch/i.html...

 

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Big heatsink is what I think, linear regulators are very wasteful in terms of energy so if your input voltage is say 19V (typical Laptop PSU output) and you want only 5V out that's a drop of 14V so at 1A - that's 14Watts of heat - it has to go somewhere

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You could just get a 19V laptop charger (£10) and feed a load of fixed voltage regulators mounted on a large heatsink mounted inside a metal box (if you are on a tight budget) and have standard output terminals 3.3V 5V 6V 8V 12V & 15V - after all how often do you need a variable supply?

 

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I agree, I knew it would get quite toasty! The LM317 is rated for 125C, so surely I would need a heatsink at better than 5C/W for 5v at 1A (which is unlikely)

EDIT: Junction to case = 5C/W + heatsink (case) to air =   5C/W

=10C/W 

x 14W

=140C (past the maximum temp)

Last Edited: Sun. Jan 4, 2015 - 12:08 AM
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Build one controlled by AVR?

http://www.tuxgraphics.org/elect...

 

Why don't you set your eBay to just look for UK offerings??!?

 

"Cheap Chinese" work great on our benches.  But I think we bought a model that others had had good luck with.

 

 

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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after all how often do you need a variable supply?

An interesting comment.  made me think.  My answer is "usually".  (And you didn't have 24V in the list...)

 

-- Generally, our AVR apps have "power supply" on board from the "raw" which might be AC or DC.  generally, we'll use a brick of the appropriate voltage for dev and test.

 

-- Being the firmware guy, when I fire up the bench supply it is often/usually to test reaction to varying supply V conditions.

 

To some extent, it is the same for our bench techs.

 

No mention of current meter or current limiting?  Bench supply nearly useless (IMO/IME) without it.

 

 

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Nope didn't propose a 24V output tap because a 19V laptop charger was suggested as a front end "brick" power source

 

I have a variable power supply with current limiting and digital display of voltage and current .... but mine was more than the £50 budget we have here

 

I suppose it depends on what you need the PSU for - to-date mine has been used mainly for powering digital electronic circuits (usually with on board regulation down to 5V and then 3.3V) so my PSU usually sits at 7-8V current limited to 1A max for this purpose

 

I agree variable is nice but then Ben needs to decide what he wants and how much he is willing to spend and also if he wants a DIY or prebuilt unit first

 

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theusch wrote:
Why don't you set your eBay to just look for UK offerings??!?

Yep - that's what I did with those links I posted

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A twist on Plons suggestion:

 

 

There are several examples out there converting an old desktop psu to a bench unit and you several voltage values from the output leads. I have an old unit around that I use for working on HDD's and other PC parts.

 

Here is one example:

 

http://www.wikihow.com/Convert-a...

Just some guy

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** WARNING ** 

 

Be VERY careful with ATX Power Supplies - those things can set stuff on fire!! - the current capability is staggering. Make sure your output rails are fused

 

I once melted the plastic insulation on hook-up wire attached to one when a short developed - scary moment as clouds of smoke poured off the wire which glowed like an electric fire element

 

They can supply 20A - 40A+ on 5V and 3.3V rails without breaking a sweat - you have been warned

 

 

 

 

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Hi again Ben,

 

I am sure that you could find some valuable advice closer to home from some of the links for maker spaces in your oscilloscope thread, etc if you can manage to contact/visit them.

 

Best of luck.

 

Ross

 

Ross McKenzie ValuSoft Melbourne Australia

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idealpcsolutions wrote:
I have a variable power supply with current limiting and digital display of voltage and current .... but mine was more than the £50 budget we have here
Linear Technology has the DC2132A variable with current limiting with no display for 200USD assembled; has two LT3081 1.5A LDOs for output.

LT3081 datasheet, last page, has a simplified version of DC2132A (fixed resistor to set the current limit).

DC2132A has design files (schematic, gerbers, BOM, ECAD of some form).

19V laptop charger - probably good quality but a flaky wall wart can cause some odd problems plus the LT3081 PSRR Is fair to poor at most wall wart output frequencies; to replace, can use a 24V SLA (or such) and an off-the-shelf 24V SLA charger.

LT3081 PSRR - excellent at: 120/100 Hz (stout unregulated wall wart), 2MHz or 3MHz and greater; some 1A+ buck voltage regulators are running at 2MHz+ (DC2132A is 700kHz).

Ref.

Linear Technology

LT3081 - 1.5A Single Resistor Rugged Linear Regulator with Monitors

Power Management LDO Linear Regulators Positive Linear Regulators (LDO)

http://www.linear.com/product/LT3081

Linear Technology

DC2132A - 24V 3A Constant Voltage, Constant Current Bench Supply Featuring LT3081, LT8612, LT3092

May 22nd 2014

Solutions Power Management Current Sources

http://www.linear.com/solutions/5086

"Dare to be naïve." - Buckminster Fuller

Last Edited: Sun. Jan 4, 2015 - 05:44 AM
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Nope didn't propose a 24V output tap because ...

"Real world" applications (industrial) done by "real" engineers (flame bait) are, basically, 24VDC.  And no, an unregulated supply that might range higher under no-load isn't the same.

 

That tweaking aside, ;) there are many app areas where your listed choices will be fine.

 

current limiting and digital display of voltage and current .... but mine was more than the £50 budget we have here...

 ...but apparently the "Cheap Chinese" are off limits?  Where do y'all draw the line?  Lessee--I can recall threads on "cheap Chinese" Arduino clones, ISP dongles, nRF modules, various "new" TFT modules with "new" controller chips, and more.  Certainly, there is a bit of risk especially for early adopters.  But you and OP never dip your toe into these waters?

 

 

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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There is actually a breakout board available for the ATX Power Supply conversion...

 

 http://www.robotshop.com/en/cytr...

They can supply 20A - 40A+ on 5V and 3.3V rails without breaking a sweat - you have been warned

 And yes - it is capable of high current outputs as shown here:

 

http://web2.murraystate.edu/andy...

 

Inline fuses would be easy to implement - the OP sounds up to the challenge!

Just some guy

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Ben, I think I can help.

 

I have a small adjustable bench PSU I no longer use and based on previous experience it'll not fetch much on eBay so I'm happy to donate it to you. It's one of these...

 

http://cpc.farnell.com/_/ps12015...

 

The deal is that I'll post it to you and all I ask in return is that you donate an amount, equal to the postage cost, to a charity of your choice.

 

Brian

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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Very nice Brian!! 

Just some guy

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+1 Brian

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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Upgrading my earlier post from "I think I can help" to "I can help".

 

I've just been in the store and the power supply, as linked to, is there so it's yours if you want it. See above for more details.

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss