Author Topic: Ballpark budgeting for a 3.3VDC power supply  (Read 843 times)

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Offline AJMansfield

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Ballpark budgeting for a 3.3VDC power supply
« on: March 21, 2017, 07:29:37 am »
I'm working on developing a product that will need to run off mains power (without any external brick) and I'm trying to figure the ballpark amount I need to budget for including a AC mains to 3.3VDC power supply on the board.
The board is already going to be handling mains-voltage stuff as part of its functionality. It only needs to supply around 300 mA for my design (150mA for the MC, 20mA for a character LCD backlight, and then few misc optocouplers and stuff.)
Volume is probably going to be somewhere from 50-5000, and it doesn't need to be terribly efficient or anything.

What is a good ballpark price to use for budgeting this?

I'm mostly using this to sanity-check my target price point to make sure there will actually be a profit margin left after it's all manufactured.

Also, if there are any more general resources about how to budget out a device like this, I'd be glad for any links or other help.

Offline evb149

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Re: Ballpark budgeting for a 3.3VDC power supply
« Reply #1 on: March 21, 2017, 08:29:12 am »
Well go to one of the IC vendors web sites that make cheap flyback converter ICs, Power Integrations is one:

I think ON semiconductor may have something similar.  Maybe others like Fairchild or so on.

Use the parametric selector to find an offline ACDC flyback IC that is recommended for your power input and output parameters.
Use their wizard to generate a reference design and BOM and layout and budgetary cost.
Modify the budgetary cost / BOM as needed in your own tools to account for anything different / special that is relevant tooo your own particular integration.  For instance since you already use mains on the product you will not need the AC input module, chokes, filters, fuse, etc. to be duplicated in all probability, so don't count those costs twice.

Not every vendor has a BOM / reference design / budgetary quote generator and simulator that is point & click but a few do.

Your costs will vary depending on if you need custom magnetics and if so in what volume or if you use something off the shelf maybe Coilcraft or someone has something close enough for your needs.  But even in volumes of hundreds custom isn't that expensive.


Offline evb149

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Re: Ballpark budgeting for a 3.3VDC power supply
« Reply #2 on: March 21, 2017, 08:37:57 am »
So you're handling mains in the product but have no other mains derived voltage rails?
If you have something like +/- 48VDC, 24V, 12V, whatever you can just buck or whatever that isolated rail to get 3.3VDC but I guess you don't have such handy.  Even going from a 350VDC PFC output rail through an isolated converter is another option, whether it saves any layout / cost issues can't be said generally.

Also for other parts of the system there are other online design wizards like TI's Webench that will design a lot of power conversion stuff for you as well as a few other things and produce BOMs, budgets,     layouts, schematics.  I'm just not aware that TI has isolated ACDC switchers like ON / PI do.  Well I know TI does have some ACDC application switchers after all they bought Unitrode that made some of the classic ones, I mean I'm not sure of what they make at the moment that is most relevant for your design as well as having WEBENCH support.  You can see if anything comes up as a sane solution from TI as well.

Fairchild has online tools of some sorts, and so as I recall might Infineon who do make stuff for ACDC and DCDC applications too.

Almost worst case budgetary would be to look at the costs of COTS ACDC isolated power modules from the likes of CUI, Vicor, TDK Lambda, whoever is selling them on Digikey / newark.  That would be a drop in solution more or less, but more costly than self-made.


Offline t_ryner

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Re: Ballpark budgeting for a 3.3VDC power supply
« Reply #3 on: March 21, 2017, 02:53:34 pm »
Hello! I did some browsing on digi-key and found these. The first one is a 5 volt regulator to put after the rectifier, and the second is a 3.3v converter that puts out 300mA. Hope I helped!

5 volt reg-

dc-dc converter-

Online mariush

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Re: Ballpark budgeting for a 3.3VDC power supply
« Reply #4 on: March 21, 2017, 06:04:16 pm »
TME (a European distributor) sells  classic transformers  ... 1.8va (12v ac 100mA) for 1.19$ if you get 100, probably cheaper if you get 500+ here's example :
2.3 va transformers are 1.26$ in 100pcs :
  .. a dc-dc converter would cost maybe 1$ (at 100+) so overall you'll be at less than 2.5$
farnell has versions with 6v AC output ... A 2.3VA isolation transformer is about 2.5$ when you buy at least 50.  If you order 500 or 5000, I'm sure you can get much lower price.  Here's an example:  (available in 110v or 230v versions)

From there, a bridge rectifier, a capacitor and a linear regulator would be less than 50 cents  if you order hundreds.
No silly certifications to get your product through, easy design (transformer has pcb pins, so it goes directly soldered on pcb, no screws or potential vibration issues etc) , only downside is maybe height of transformer and maybe weight and maybe the fact that your product may not be under 0.5w when in standby or whatever the number is these days (EU certifications)

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