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Author Topic: 24V to 5V 1amp max  (Read 2175 times)
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Wizpic
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« on: April 02, 2015, 10:11:46 22:11 »

I need to convert a 24V dc supply to 5V dc supply with a max current of 1A(nominal 600ma), tried the LM2594HV which gives 500ma output but when running it drops to 3.8V which is causing issues. I think this may be caused by PCB layout but the trouble is I need to hard wire it on Vero board as it's a one off unit also looked at LM2575T-5.0/NOPB  but I think I will face the same issue as the LM2594,so I've looked at other ways thought of using  LM7812 then LM7805 to help reduce heat, it's not running continuous may be for an hour or 2 at a time.
Can anyone recommend other ways or would you think LM7812-LM7805 work with out to much heat (can mount them on heatsinks to help)
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metal
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« Reply #1 on: April 02, 2015, 10:23:01 22:23 »

You need a transistor pre-regulator to use 7805/7812:

http://sound.westhost.com/project102.htm
http://www.edaboard.com/thread270372.html
Images from google search


This might also give you more ideas, called black regulator, but this is off-topic:

http://www.romanblack.com/smps/smps.htm
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j0k3r
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« Reply #2 on: April 03, 2015, 12:20:27 00:20 »

On my all, 95% projects, i´m using switching regulator´s Smiley.

For your case you could try using LM2576. It´s over dimensioned but you never have problems,(i have more than 1000 units on field on more than 10 years, at ~750mA in continuos operations ~12 hours a day).

A good PCB layout is essential for best results.
I left the linear regulator on the rest 5% just for more sensitive applications. But in some cases there is a switching regulator before and a linear after.
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pickit2
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« Reply #3 on: April 03, 2015, 10:37:49 10:37 »

I bought this on ebay using LM2576 less than £1 each inc p&p

DC-DC Step Down Buck Voltage Converter Module LM2576
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cerebronico
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« Reply #4 on: April 03, 2015, 04:03:37 16:03 »

I switched to OKI-78SR-5/1.5-W36-C, cost about $4.50 each at Newark
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Wizpic
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« Reply #5 on: April 03, 2015, 06:10:38 18:10 »

I shall have a look at those cc/dc converters and just plug it in. As  I think my issue is not been laid out on pcb and been hard wired.
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« Reply #6 on: April 05, 2015, 09:49:46 21:49 »

I've used an LM2576  module from DealExtreme. Simple & cheap. Only problem with DealExtreme is their slow shipping, so as pickit suggested looking at eBay may be faster. Either way, using a cheap pre-built module is certainly the way to go for prototyping.
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« Reply #7 on: April 11, 2015, 09:16:03 21:16 »

Sorry if my reply comes delayed (been far from civilization for 6 weeks), but have any of you considered the TPS family from Texas? They provide from few Amps to 25A with great efficiency (read reduced heat dissipation) on a tiny footprint.

See my test here: http://www.sonsivri.to/forum/index.php?topic=56432.0. Easy to achieve as it is a SOIC package.

Really, let's get "back" to 2015 Smiley.

LE: the TPS family accepts even up to 60-100V (some) input voltages. The WEBENCH online designer gives you all BOM, schematic ain in many cases and a proposed PCB layout, while a thermal analysis is also possible. The online designer is only for registered users (well, you just register, no obligation afterwards Smiley).
« Last Edit: April 11, 2015, 09:21:19 21:21 by thunderer » Logged

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« Reply #8 on: April 12, 2015, 01:01:23 01:01 »

I rebuilt the supply at home and took it up to 500Ma and it worked,So when I got back to work I carried  further investigation and I found that I connected the diode to the wrong side of the inductor, Remade the connection to the correct side and it works perfect, This is the trouble by hard wiring it and distractions at work, Only its a one off unit and did not want to go through the hassle of making PCB.

 thunderer that look interesting will look into that for other designs I got lined up
 
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« Reply #9 on: April 12, 2015, 09:37:37 09:37 »

Did you try: LM1084ADJ.
I suggest you to check it.

take care,
Manuel.

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metal
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« Reply #10 on: April 12, 2015, 11:19:17 11:19 »

man.. Im looking at 7805 datasheet, first glance you don't have any problems, you can input 24V and get 5V @ 1A without any problems.
« Last Edit: April 12, 2015, 11:21:22 11:21 by metal » Logged

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« Reply #11 on: April 12, 2015, 11:56:45 11:56 »

In that case you'd be expecting the 7805  / LM1084ADJ (both linear regulators) to dissipate (24 - 5)V x 1A = 19 W, that's a serious heatsinking problem from such a small package. As previous replies have said there are many integrated switching regulators that can do this job with 90% + efficiency and no external components, many more if you're prepared to use a switching controller plus external MOSFETs and inductor. Burning 24W to achieve a 5W supply isn't cool.
« Last Edit: April 12, 2015, 12:06:37 12:06 by UncleBog » Logged
metal
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« Reply #12 on: April 12, 2015, 12:03:12 12:03 »

especially in a country where summer is really hot, the cost of heatsinking becomes an issue, add to it that most switching regs for the task in hands for this topic can be done using switching regs without heatsinking as suggested by thunderer. I don't know why wizbeer wants to use the old-fashioned way, may be he's getting ridiculously older..
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« Reply #13 on: April 12, 2015, 04:57:10 16:57 »

I don't know why wizbeer wants to use the old-fashioned way, may be he's getting ridiculously older..
Less of the old  Cheesy
I did not want to use the old LM7805 regulator (this would of been last resort) , in the end I used LM2594HV has I add few lying around in box of bits, my problem was caused by me, May be to much wizbeer inside  Grin

it's all working fine now with everything powered up and on (which would never happen but in case) it draws 300-450Ma at the max   
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« Reply #14 on: April 12, 2015, 06:40:39 18:40 »

now you are just a wizhum Grin

show us some photos, schematics!
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« Reply #15 on: April 14, 2015, 12:58:10 12:58 »

I need to convert a 24V dc supply to 5V dc supply with a max current of 1A(nominal 600ma), tried the LM2594HV which gives 500ma output but when running it drops to 3.8V which is causing issues. I think this may be caused by PCB layout but the trouble is I need to hard wire it on Vero board as it's a one off unit also looked at LM2575T-5.0/NOPB  but I think I will face the same issue as the LM2594,so I've looked at other ways thought of using  LM7812 then LM7805 to help reduce heat, it's not running continuous may be for an hour or 2 at a time.
Can anyone recommend other ways or would you think LM7812-LM7805 work with out to much heat (can mount them on heatsinks to help)

couple of month in elektor a nice switch mode 5V regulator 1amp design published i made it and working with out any problem
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« Reply #16 on: April 14, 2015, 06:56:00 18:56 »

couple of month in elektor a nice switch mode 5V regulator 1amp design published i made it and working with out any problem
What month ??
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« Reply #17 on: April 14, 2015, 11:08:02 23:08 »

seriously, give more info in one post...!
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« Reply #18 on: April 15, 2015, 12:58:35 00:58 »

What month ??

seriously, give more info in one post...!


I couldn't agree more.  Very frustrating to have to search through back-issues when a post {sadman} gives only a teaser and no real information.

Working backwards, unless I missed something, the most recent switch-mode 1A regulator article I can see in Elektor dates back to November 2012, page 16, entitled 'Farewell 7805 & 7905
Switch-mode replacements do a much better job'  by Raymond Vermeulen (Elektor Labs).  That design doesn't fit the requirement here though as the input range is only up to 17V.

A more recent, though non-switched, article is a simple LM317 circuit entitled 'LM317 Turns 78xx', page 99 of the July/August 2014 issue.  1.5A max, 40V max differential but comparatively low efficiency.

Then there's the article 'MagI³C-VDRM. A voltage regulator and then some…' on page 56 of the October 2014 issue which is interesting but only a component review not a constructional article.
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« Reply #19 on: April 19, 2015, 09:21:24 09:21 »

Hi
I use TPS5430 from TI - I place this SW regulator in all of my designs - easy to use and work 100% all the time.
Remember to have good layout design according to data sheet example.
This small foot print regulator can provide up-to 3A of current with voltage input up-to 36V

All the best

Bobi
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« Reply #20 on: April 19, 2015, 03:23:42 15:23 »

you can use the classic MC34063, very robust and cheap
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jumulab
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« Reply #21 on: April 24, 2015, 06:44:43 18:44 »

Take a look at chinesse products at Ebay ( for example : http://www.ebay.co.uk/itm/5A-Lithium-Charger-CV-CC-buck-Step-down-Power-Supply-Module-LED-Driver-fnxt-/161676131978?pt=LH_DefaultDomain_0&hash=item25a4a5fe8a).
You can check the device and work accordly.
I have using these devices in machines  connected continously whitout any problem.
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« Reply #22 on: April 24, 2015, 08:40:31 20:40 »

Honestly one of my favorite places to order any DC/DC converters has been prodctodc.com.  Shipping is not too bad considering it's from China, quality has been acceptable on most items (a few passives on really cheap $2 boards are sometimes skewed) and they have a wide selection.

It's not quite a replacement for rolling your own solution from scratch, but sometimes the time investment is better spent elsewhere.
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« Reply #23 on: June 10, 2015, 07:18:28 07:18 »

I have used recom dc -dc converter for 24  to 3.3 v with 1 Amp current and it is not heating at all after running 24X7. In this series you can use        R-78B5.0-1.0. The R-78Bxx-1.0 Series high efficiency switching regulators are ideally suited to replace 78xx linear regulators and are pin compatible.Efficiency up to 97%,Non isolated,no need for heatsinks.
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Bharat Sujanani
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« Reply #24 on: August 13, 2015, 06:18:15 06:18 »

Last months Silicon Chip (July 2015) had a nice little switch mode psu design using Richtek RT8299 3A 24V buck convertor. They were using it with 5V output from 12V automotive power for USB charging in a car.

If there is any interest (If anyone wants to roll their own)  I can scan the article. From memory the board was single layer so would be pretty easy to replicate even with a home pcb process.
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