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I found this and I'm a little confused.top view of SMPS

It appears to be a simple component in to which I can put mains voltage and out of which get 3.3V DC without needing any other components - precisely what I want. Maybe I'm missing something, but from various googling this doesn't seem to be common, or used in circuits as a component of its own.

Could I, for example, use this single component to run an Arduino from mains? (there is a 12V version here)? Or to charge a mobile phone? Or, in my specific case, to connect a mains supply to a 3V relay 24/7 using minimal standby power.

Assuming I've understood what this component does, is there a better name for it? Googling "encapsulated electronic transformer" only returns this MYRRA product, but surely this is a generic thing... or is it?

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  • \$\begingroup\$ That's an SMPS. Look for "power supplies", really. \$\endgroup\$ Mar 13, 2018 at 11:15
  • \$\begingroup\$ I'd probably call it a "power supply module" (which is of course quite a broad category) \$\endgroup\$ Mar 14, 2018 at 0:23

4 Answers 4

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This component does what you expect. It takes AC mains as input, and outputs the specified DC voltage (at the specified power). It is actually made of a switched-mode controller and transformer, all integrated in a small plastic cube.

It is a rather common component used mainly for simple appliances requiring relatively low power, where the designers don't want to waste time designing a specific AC-DC supply. It seems perfectly appropriate to use them for the usages you describe. Of course, for high-volume products, designers usually go through the hassle of designing their own, because it can make the product cheaper. This is why it is not usually found in consumer products.

There is a wide choice for these components available from distributors, and is typically called "AC/DC power module". See those available from Mouser, for example.

Note: this component is galvanically isolated, so you need to be careful in your layout to maintain the isolation between primary and secondary. Just don't route the AC mains side and secondary side traces close to each other.

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There isn't a single standard name, but most people would expect a PC-mount power supply to be something like what you show. At least one distributor lists such things under On-Board Power Supplies.

Other possible interpretations

I thought the salient part you cared about was that it is one simple device that you can mount right on your PC board.

If you just want to convert line power to DC, then that's any power supply.

If you want it to be a switching power supply (you might care about size, efficiency, and heat produced, but how those specs are met shouldn't really matter), then switching power supply, SMPS, or even just switcher would do.

If the point is to have a single block like you show, then use encapsulated power supply, or less formally power brick.

If the point is to be able to solder it directly onto a PC board, then see my original answer above.

You question is like showing a picture of a orange, then asking what it is. Fruit, citreous fruit, orange, and spheroid are all correct answers without you specifying what aspects you care about or what level of detail you want to know about.

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  • \$\begingroup\$ Isn't SMPS the standard name as per Leon's answer? \$\endgroup\$
    – fishkake
    Mar 13, 2018 at 11:58
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    \$\begingroup\$ @fishkake SMPS is much, much more general. It is, for example, also used to name the big power supplies that you find in computers. If you need a term clearly identifying these small supplies you solder directly on PCBs, the generic "SMPS" name isn't specific enough. \$\endgroup\$
    – dim
    Mar 13, 2018 at 12:05
  • \$\begingroup\$ To continue your analogy - if I showed a picture of an orange it might be very obvious that the required answer was "it's an orange" depending on the context of the question - I thought that in this case there would be a similarly obvious required answer, the "single standard name" which, as you say, doesn't exist. But I've learned a lot from these answers, so thank you for that. \$\endgroup\$
    – fishkake
    Mar 13, 2018 at 12:46
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The data sheet shows a block diagram and describes it: -

enter image description here

Generically it is a switch mode power supply (SMPS).

Could I, for example, use this single component to run an Arduino from mains? (there is a 12V version here)? Or to charge a mobile phone? Or, in my specific case, to connect a mains supply to a 3V relay 24/7 using minimal standby power.

The only caveat is ensuring it provides enough load supply current and that some (older) phone chargers might have a more constant current output meaning this device won't be suitable across the board.

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You should read the web page properly. The description tells you that it is a switched-mode power supply, SMPS or "switcher".

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    \$\begingroup\$ I did read it. Several times. But isn't this also a SMPS ?uk.rs-online.com/web/p/… My question was what sets the product I linked apart from other SMPS transformers. \$\endgroup\$
    – fishkake
    Mar 13, 2018 at 11:42
  • \$\begingroup\$ Nothing. They are all basically the same. \$\endgroup\$ Mar 13, 2018 at 11:47
  • \$\begingroup\$ The product I linked says "With the same footprint as a EI30 transformer, they will replace the 50 Hz Transformer, Fuse, Bridge Rectifier, Regulator and Filtering Capacitor" - so if they're all the same, is that what SMPS means? That would make sense. Perhaps I should have made that my question. I thought this product was a SMPS transformer plus something else, but if all SMPS transformers include the rectifier, regulator etc that is much clearer. \$\endgroup\$
    – fishkake
    Mar 13, 2018 at 11:56
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    \$\begingroup\$ Sorry. The item you mentioned in your comment is just the transformer, it needs a lot of additional circuitry to make an SMPS. Most of the circuitry can be obtained as an IC from companies such as Linear Technology. \$\endgroup\$ Mar 13, 2018 at 12:24
  • \$\begingroup\$ Aha! There is a difference between "SMPS" and "SMPS transformer"! I didn't understand that. I thought those two things were like saying "Cantaloupe" vs "Cantaloupe Melon" - two ways of referring to the same thing. Now I see that actually a "SMPS Transformer" is a COMPONENT of a SMPS, not just a longer name for one. Right...? \$\endgroup\$
    – fishkake
    Mar 13, 2018 at 12:37

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