# " 36W SMPS design " help needed...!!!

Discussion in 'The Projects Forum' started by mishra87, Aug 5, 2016.

1. ### mishra87 Thread Starter Member

Jan 17, 2016
170
2
Hi all,

I want to design SMPS under below specification :

Input : 85-265VAC , 50Hz
Output - 24@1.5A

Could anybody guide me defining schematic and components selection.

Thanks !!!

2. ### AlbertHall Well-Known Member

Jun 4, 2014
1,971
389
Cheaper, quicker, safer.

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3. ### mishra87 Thread Starter Member

Jan 17, 2016
170
2
Our product suppose to be driven by this SMPS.

So it's application specific and I can not buy it...!!!

I have posted this thred for some guidance.

I also know to buy a better option.

Anyway thanks...!!!

Apr 5, 2008
15,652
2,348
Hello,

Perhaps you can find some info in the attached PDF from ON.

Bertus

• ###### smpsrm_d.pdf
File size:
1.3 MB
Views:
16
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5. ### Papabravo Expert

Feb 24, 2006
10,179
1,800

1. Your output power will be 36 Watts
2. Assume an initial efficiency of 80%
3. Input power will need to be 36 Watts / 0.8 = 45 Watts
Now look at your input range of 85 VAC to 265 VAC
1. @85 VAC, 45 Watts implies an input current of .53 Amps (RMS)
2. @ 265 VAC, 45 Watts implies an input current of .17 Amps (RMS)
If you convert the line voltage to DC using a power transformer you get
1. 85 VAC ⇒ ≈ 120.2 VDC
2. 265 VAC ⇒ ≈ 375 VDC
In relation to your output voltage you have the following ratios:
1. 120.2 VDC / 24 VDC = 5
2. 375 VDC / 24 VDC = 15.625
This wide input range has to be factored into your converter topology and will tell you what kind of duty cycle will be required and how precise the output regulation will be for a buck topology. In my estimation this will be a heavy lift.

As an alternative you could use the DC voltage in the range [120.2,..., 375] to create a high frequency square wave which you then pass through a smaller transformer that would step the voltage down by a factor of 10 giving an AC range of 12 VAC to 37.5 VAC. Now you rectify and use a buck boost topology to get your 24 VDC output. There are just too many alternatives to tell you what to do without a better understanding of your requirements. You're the designer after all, so put up a design and see if it flies. Simulate it, breadboard it, build it, do what you need to do.

If you don't have the time or the resources to do that, then by all means hire somebody who does, or buy it off the shelf as has already been suggested.

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6. ### tcmtech Well-Known Member

Nov 4, 2013
2,046
1,679

That makes no sense. If it requires 24 volts at up to 1.5 amps how will it know whether it's being powered by a SMPS you built Vs one built by someone else?

7. ### mishra87 Thread Starter Member

Jan 17, 2016
170
2
Thank you so much !!!

This information is really worth for me and that is what I was looking for...!!!

If you can suggest me....
Which manufacture primary switcher ie. PWM ic I need to select for realiabilty purpose and ease of implementation....!!!

I have already worked on Power integration TOP switches up to 12 watt.

If any other manufacturers can do the same job.

Thank you so much once again...!!!

8. ### mishra87 Thread Starter Member

Jan 17, 2016
170
2
As i already told its application specific requirement and end application is PS for water Auro .
Thats All !!!

9. ### mishra87 Thread Starter Member

Jan 17, 2016
170
2
Shall I look for flyback topology...!!!

10. ### tcmtech Well-Known Member

Nov 4, 2013
2,046
1,679
Because unless you are very familiar with designing and building your own SMPS units and have all the necessary design software, fabrication machinery and tooling in place, which you obviously don;t being you're here asking us for help, buying off the shelf mass produced ones is way cheaper,easier and more relible to work with.

Do you really think you can build this or something better than this in the same or smaller size and efficiency range , http://www.ebay.com/itm/Mean-Well-R...610852?hash=item2a6d6ee624:g:EoYAAOSw-YVXnAeK , for less than \$10 American equivalent in your area?

I doubt anyone here could. I know I couldn't. My time alone at a \$1 an hour would be well beyond the purchase price before any single component was purchased.

That's why us guys who have worked with this sort of stuff to any degree always recommend buying ready made units rather than trying to build them. Especially so if the power requirements fit into a common voltage and current range like yours does.

BTW had you did an online search for "SMPS circuit" you would have been overwhelmed with information, circuit diagrams and solutions to your problem.

11. ### AlbertHall Well-Known Member

Jun 4, 2014
1,971
389
And if it needs to be isolated, designing the main transformer is definitely a specialist job.

12. ### tcmtech Well-Known Member

Nov 4, 2013
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1,679
That's just it.

Designing anything more than a basic buck or boost converter SMPS requires fairly specialized transformer components that not just anyone can buy or build themselves which leave most people with having to use something like PB's hybrid linear power supply that's based around a standard iron core primary transformer that does the isolation and bulk of the step down work followed by a simple buck or boost system to do the remaining regulation and related work which by design having an iron core transformer up front makes it bulky and very limited in what input voltage range it can work with without having to switch taps on the primary.

It's certainly doable but it's far from being a universal input type unit that's compact, simple, efficient, and cheap.

13. ### wayneh Expert

Sep 9, 2010
12,156
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If a friend asked you how to get some Cabernet Sauvignon from Napa Valley, would you tell them to go buy grapes?

14. ### Papabravo Expert

Feb 24, 2006
10,179
1,800
I don't think the flyback technology will work for you. Your main problem with the universal input you have specified is reducing an enormous DC voltage range down to one that is more manageable.

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15. ### tcmtech Well-Known Member

Nov 4, 2013
2,046
1,679
What I don't get about these sort of threads is everyone who starts one 'needs to build theirs because it's a special application and an off the shelf one won't work' yet their power requirement specs, like this ones 24 VDC @ 1.5 amps, fall well within the range of mass produced dirt cheap units capabilities.

Jun 22, 2012
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17. ### tcmtech Well-Known Member

Nov 4, 2013
2,046
1,679
Dang! you beat my \$9.95 price one and you got free shipping too.

18. ### wayneh Expert

Sep 9, 2010
12,156
3,063
\$3.29 delivered!? That's crazy cheap.

Darn it, now I want one.

19. ### tcmtech Well-Known Member

Nov 4, 2013
2,046
1,679
Actually, you have to go and choose which power supply you want. They have a bunch to pick from but still the 24 VDC 36 watt unit is still under \$5.

Yea it makes me want one too but at that price, I might as well order 5 - 6 of them for just in case.

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