Can someone explain how I can convert 220 V AC 60 Hz to 12/5 V DC, 500 mA/1A without using any transformer? Like Sonoff or Shelly power supply.

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Thank you so much

  • 4
    \$\begingroup\$ such a power supply cannot have its output accessible to the user ... touching any exposed part of the power supply and any part of the device that it powers can be fatal \$\endgroup\$
    – jsotola
    Jul 5, 2021 at 3:00
  • 1
    \$\begingroup\$ Who says they don't use an internal HF transformer? \$\endgroup\$
    – Andy aka
    Jul 5, 2021 at 9:00

2 Answers 2


1A is a bit much for the classic trasformerless dropper (wh1ch just uses capacitors to produce a current source that's then regulated by a shunt regulator)

It appears that the Shelly uses a non-isoated buck converter to drop the up-to 350V it gets from the from rectified mains supply down to a lower voltage to run the system.

As a result every part of the circuit is live (and thus deadly)

If you want a safer power supply for experimenting consider using a phone charger.

  • \$\begingroup\$ sonelec-musique.com/electronique_bases_alims_sans_transfo.html \$\endgroup\$
    – Antonio51
    Jul 5, 2021 at 6:35
  • \$\begingroup\$ @ Jasen ... Ok, it is in french ... but Google does translate. The link is for some infos about power supplies without transformers but for low currents . Other ways are flyback SMPS ... with or without isolation. There are a lot ... See www.ti.com note and software "Designer Tools"... for quasi all SMPS power supplies. \$\endgroup\$
    – Antonio51
    Jul 5, 2021 at 7:07
  • \$\begingroup\$ That is the "classic trasformerless dropper" discussed in paragraph 1. \$\endgroup\$
    – Jasen
    Jul 5, 2021 at 7:09
  • \$\begingroup\$ Yes. Added another information for "all" other types. ti.com/tool/… \$\endgroup\$
    – Antonio51
    Jul 5, 2021 at 7:24

Rectification followed by PWM and then smoothing using a capacitor. But since you want two output voltages, you would have to have two PWM's. Probably a regulator as well. This is just a high-level way of looking at it. Rectifier would have to be selected to accommodate the high voltage, and current requirements.

There are other ways of doing it.

  • \$\begingroup\$ no no,need only one of them,12v or 5v not both \$\endgroup\$
    – Dave
    Jul 6, 2021 at 1:41

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