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Simple Power Supply Question
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Re: Simple Power Supply Question

by zener on Thu Sep 23, 2010 5:20 pm

westfw wrote:It may be more economical to find an AC power supply that meets your needs, and power it from one of those common and inexpensive Automotive "AC Inverter" boxes.

Ya had me then ya lost me...

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Re: Simple Power Supply Question

by westfw on Thu Sep 23, 2010 8:20 pm

It may be more economical to find an AC power supply that meets your needs, and power it from one of those common and inexpensive Automotive "AC Inverter" boxes.

It should be relatively easy to find or even build (using transformers and other "old school" power supply fundamentals) a power supply that provides +/-12V@1.5A from a standard 110VAC wall socket.

Then you take one of those consumer "inverter" gadgets that converts your car's "auxiliary power socket" to 110VAC (eg http://www.amazon.com/Duracell-Digital- ... B001TLY4D8 ) and use that to power the input of your AC supply.

Probably not very efficient, but ... this is a car or truck we're talking about, right?

Now you have a device that you can plug into your wall as well as your car (by leaving out the inverter), and a gadget for your car that will let you power other AC gadgets as well (leaving out the DC side, or by using one with sufficient power for both.)

Be careful of power ratings, though. Final output of +/-12@1.5A in a conventional AC supply probably means that you're regulating +/-16V@1.5A at some point, and transformers aren't 100% efficient, so your INPUT to this supply might be 100W, and who knows if that 200W inverter is 200W input, or output, or even honest...

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Re: Simple Power Supply Question

by zener on Thu Sep 23, 2010 9:21 pm

No car involved...
msymms wrote:What I have is a 12 volt bench PS I have for my radios. I have a project with a need for +/- 12V with 1.5A on each side, or as close to that a I can get.

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Re: Simple Power Supply Question

by msymms on Thu Sep 23, 2010 11:49 pm

Thanks for all the replies. Maybe I have bitten off more than I can chew .... but here is my project, whether more complicated or expensive than it should be: i wish to make a portable/detachable variable power supply, with independently variable +/- outputs; using my existing bench psu or even an automobile power socket as the source. It can be expanded upon but that is the gist of it.
The point here is no so much economics but seeing the idea come to life. Very similar to hobby furniture makers with shops in the garage. The homemade furniture is unique, but always more expensive than something ready made that merely offers the same functionality. Of course, that ideal does have limits.

- mark
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Re: Simple Power Supply Question

by westfw on Fri Sep 24, 2010 1:06 am

Ah. It is probably easier to go straight from the wall to a +/-12V supply than to start from 12VDC. Probably. Especially if you want variable voltages. Search for "bipolar tracking power supply."
Note that this will be somewhat easier if you're willing to put up with a bit less than 1.5A; It looks like there is a pretty simple LM317/LLM337 circuit out there... (there are a fair number of such circuits in the audio world, and in the pre-digital op-amp electronics experiments world.)

One trick, given a not center-tapped transformer, is to set up a voltage doubler circuit to get the +/- NV from an N Volt transformer.

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Re: Simple Power Supply Question

by msymms on Fri Sep 24, 2010 11:56 am

Okay so let's just make this simple. And I do thank you very much for the replies, I am trying to learn something that has eluded me for years. I'll start with a center tapped mains transformer with output in the 15-18V range (15-0-15), then into a rectifier/bridge that will give me the +/- rails I need. Then into a LM317/LM337 circuit to regulate. I do want independent outputs, not tracking. This will be a lab/bench PSU for projects and testing. Is 1.5 amps sufficient, for small projects like found on this site and some audio projects, or is it overkill. I do know that one project I have in mind requires 600ma.

I hope I am using these terms correctly.
Once I can get this working, I want to add digital read out for voltage and current on both outputs. Finally, control it with a microcontroller. Learning as I go. But I need to walk before I run.

-mark
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Re: Simple Power Supply Question

by westfw on Fri Sep 24, 2010 12:13 pm

Yes, that sounds fine. Benchtop supplies rapidly gain in complexity (do you want separate current limiting? Output voltages below 1.25V?), but I rate by benchtop supply as one of the more useful test equipment purchases I've ever made, and I usually use it below 1A...

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Re: Simple Power Supply Question

by msymms on Mon Oct 04, 2010 1:09 pm

Hi All,
Ready to start ordering parts. Will this transformer do the trick? I am not quite sure of the specs listed and what they all mean.

http://www.mouser.com/ProductDetail/Tyc ... %252bI4%3d

I am going by the circuit design for the lab voltage regualtor in the datasheet for the LM337 page 6.

-mark
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Re: Simple Power Supply Question

by zener on Mon Oct 04, 2010 2:22 pm

I think you wil only get +- 12 out of that at 1.5A, minus the dropout of the regulators, so about +- 10V. I could be wrong however...

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Re: Simple Power Supply Question

by msymms on Mon Oct 04, 2010 2:31 pm

Yeah, I was curious about that. The datasheet shows series output at 48V at 0.75A while parallel output at 24V at 1.5A. Does this mean ± 24V when connected parallel?

-mark
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Re: Simple Power Supply Question

by oPossum on Mon Oct 04, 2010 3:26 pm

Each of the two secondary winding is 12V at 1.5A. Should be good for 13 volts regulated at full load or about 15 volts regulated with a light load if you use a single full bridge. You will need a big heat sink to get any significant current at low voltages.
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Re: Simple Power Supply Question

by oPossum on Mon Oct 04, 2010 3:30 pm

msymms wrote:Yeah, I was curious about that. The datasheet shows series output at 48V at 0.75A while parallel output at 24V at 1.5A. Does this mean ± 24V when connected parallel?

-mark


That is the -8048RF65 not the -8024RF65
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Re: Simple Power Supply Question

by msymms on Mon Oct 04, 2010 3:41 pm

Right wrong link. So, will the 8048RF65 suit my needs?
I knew I would need a good heat sink. I was considering adding a small fan as well.

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Re: Simple Power Supply Question

by zener on Mon Oct 04, 2010 4:43 pm

Keep in mind the LM317 has a max power spec of 20W. You might look into a design with an external pass transistor in a TO-3 package. I think that is how the bench supplies are often done. Yes you will need a big heat sink and fan, depending on what V out and current you use it at. Without a heat sink it is good for a watt or so.

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Re: Simple Power Supply Question

by oPossum on Wed Oct 06, 2010 1:32 pm

Low cost bench supplies often use LM723 with 2N3055. That combo allows voltage adjustment down to zero, adjustable current limiting and about 3 amps.
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Please be positive and constructive with your questions and comments.