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I have an ultrasonic cleaner bought in US, so made to work with 110V, but I would like to use it in EU, so with 230V.
The power supply in the cleaner is pretty simple, so I tried to understand how it works.

I have drawn the full schematic of this power supply(see image 1), and it has a part that I fail to understand, with the relay K1, C3 & C4 capacitors and D3 & D4 diodes.
The thing is when the relay is turned on the capacitors C3 & C4 do not affect the circuit in my understanding(see image 2), so the can't really understand why they are in the circuit in first place.

Could someone please explain me why it is done it such way, and how and if I can convert this circuit to 230VAC. 1st image

2nd image

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  • \$\begingroup\$ Why not buy a cheap 2:1 travel transformer? The power requirements look pretty modest so it shouldn't cost a whole lot and you won't have some potentially dangerous kludge on your hands. \$\endgroup\$
    – vir
    Commented Oct 7 at 21:45
  • \$\begingroup\$ Yeah, I thought about it, but I also want to learn from this opportunity. Also a new ultrasonic cleaner from Aliexpress would probably cost less the the transformer, and it is the only device I have that requires 120V, so it would be pretty pointless :) \$\endgroup\$
    – vorobey
    Commented Oct 7 at 22:09
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    \$\begingroup\$ How many Watts does it consume? If you have 2 230V incandescant bulbs/halogen bulbs of e. g. 60W, you could use them as voltage divider - perhaps a load of 10W would still work? Or take 8 old, unused notebook SMPS with ca. 19V output, use the output in series for supply of C6 and a 5V USB charger for powering C2, ... Search for an very old (heavy) device with a 110/220 VAC switch - and look inside, is there a transformator? Power of that transformator in Watts? \$\endgroup\$
    – BitLauncher
    Commented Oct 7 at 23:06
  • \$\begingroup\$ Are you sure about that power transformer connection?? \$\endgroup\$
    – Fred
    Commented Oct 8 at 0:09
  • \$\begingroup\$ @Fred, that is not a power transformer, but a common-mode filter choke, to keep RF out of AC mains. \$\endgroup\$
    – DrMoishe Pippik
    Commented Oct 8 at 16:06

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