This is a fun, light-hearted question and not meant to be taken too seriously.

As a little fun thing between a group of friends, we found this question on a desk at work sometime ago about a PCB that had been removed from a typical household object. The question basically was what household object do you think this could have come from and what could the function of the board be.

We've come up with all sorts of possibilities such as a smoke detector, microwave oven, old TV, etc, however none of us can confirm whether any of us are right as there isn't any answer to the question available. Given the large number of capacitors and resistors, we don't think it's a simple clock. Furthermore, we haven't been able to deduce what the large plastic piece in the middle is - we're hovering towards a transformer (some are thinking it's a speaker), but the shape of it is throwing us off.

Can anyone shed some light as to what they think this board could be from or what they think it is used for so we here can stop debating on this.

Battery is there for size reference.

enter image description here

Different image also of a similar device enter image description here

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    \$\begingroup\$ It might help to write relevant marks/texts printed on the PCB, and also the type of ICs if they are not too common. \$\endgroup\$ – Michel Keijzers Dec 9 '19 at 22:08
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    \$\begingroup\$ Most likely switched power supply, mains end at the bottom (of the right image), low voltage part at the top. Being the stand-alone PCB without any extra circuity, it likely comes from power supply adapter (either "wall-brick" or something similar). But I'm guessing only, of course. \$\endgroup\$ – Martin Dec 9 '19 at 22:17
  • \$\begingroup\$ Just like @Martin said, it is a mains input switching mode power supply for some device. Obviously impossible to say for what device. \$\endgroup\$ – Justme Dec 9 '19 at 22:28
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    \$\begingroup\$ This is unanswerable, because while it's pretty obviously a switched power supply there's no way to say what it is for or from. Also, SO is for serious questions, there are other places online where you can play "name that ware". \$\endgroup\$ – Chris Stratton Dec 9 '19 at 22:29
  • \$\begingroup\$ I appreciate the help. I apologize if this is against website rules, please delete the question. I don't think I can delete it since it has answers \$\endgroup\$ – timothy Dec 9 '19 at 22:36

What you've got is a switched mode power supply. Mains AC goes in at one end and well regulated DC comes out at the other. There are a few clues:

  • The obvious one is the switching transformer in the middle and the "no-man's land" beneath it on the underside of the PCB. The combination isolates the low voltage side from the mains.

enter image description here

Figure 1. SMPS block layout. Source: Wikipedia Switched mode power supply.

  • The red leads at the bottom are the mains input.
  • The mains is rectified to high-voltage DC by the four diodes beside the blob of goo.
  • The large capacitors beside the diodes smooth out the rectified AC. The voltage on these capacitors is typically one and a half times the nominal mains voltage and DC. It can hurt or kill!
  • The 8-pin chip is the switching regulator. It switches the DC supply to the transformer at high frequency - maybe 100 kHz - creating an alternating signal that can be transmitted through the transformer. I can't see it but usually there is a largish transistor to switch the power rather than the chip doing it itself.
  • On the top of the board we see some more diodes and capacitors to rectify and smooth the DC output.
  • Finally we need some feedback from the output to increase or decrease the switcher as required to maintain the correct output voltage. The feedback needs to be isolated so the 4-pin opto-isolator on the right of the transformer provides this. Internally there is an LED and a photo-transistor separated by a transparent isolator capable of withstanding 1000 V or so.

What item could this PCB board be from?

It could be from anything requiring an isolated low-voltage regulated DC supply.

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