I have an HTronic 19 00 33 AC/DC converter. I would like to use it as a DC/DC step down converter to transform 12V DC into 5V.

HTronic 19 00 33


I could not find the datasheet in English, here is the German version.

As far as I understand, it uses 4 M7 1N4002 diodes and a 2000uF capacitor to convert AC to DC, and then a LM317T to step down the voltage.

With my very little and new electronics knowledge, if I connect DC to the input it should just work and two of the four diodes will let the DC flow, and the others two will always block it. My concern is that I might be missing some parameters in my limited logic.

  • Is there any problem if I connect DC to the input?
  • Can the M7 diodes receive constant 12V as an input instead of AC?
  • In case there are problems, can I connect the DC after the diodes or I should remove the diodes and capacitor instead?
  • 1
    \$\begingroup\$ general advice: 12V -> 5V, that's 7V in drop. Your linear regulator device thus have to (conservation of energy) dissipate 7V · I in heat, with I being the current you draw. You normally simply wouldn't use a linear regulator here (and the LM317 is an ancient one, atop of that), but a switch-mode supply, where the voltage isn't dropped over a transistor junction that gets hot, but instead energy is stored, and "released" in a controlled manner from an inductor's magnetic field. It feels like you'd be using a solution that's bad by design. \$\endgroup\$ Commented Oct 6, 2020 at 8:55
  • \$\begingroup\$ This sounds like a cobbled together idea. If you need a regulator then use a straight-forward DC-in regulator circuit. \$\endgroup\$
    – Andy aka
    Commented Oct 6, 2020 at 9:02
  • \$\begingroup\$ @Andyaka, true... just want to know if i should trash this device or if i can give it a useful life. Also and more important, In my head this should just work, and with these types of questions I usually learn a lot ;) \$\endgroup\$ Commented Oct 6, 2020 at 12:56

1 Answer 1



The beauty of using the full bridge rectifier diode (which is 4 M7 Diode in your circuit) is that you can input DC directly to the AC-DC converter, It should work fine. Even if you reverse the polarity of DC input it should also work.

  • 2
    \$\begingroup\$ there might be thermal considerations (instead of every of the four diodes having ca. 50% duty cycle and 50% "cool down" cycle, you get two diodes running continously), but that can be addressed by not drawing more than half the maximum output power. \$\endgroup\$ Commented Oct 6, 2020 at 8:52
  • 1
    \$\begingroup\$ Thank you! Another very interesting thing i never though about, is connecting a LED to AC, i guess it flickers, but too fast to see it \$\endgroup\$ Commented Oct 6, 2020 at 8:52
  • \$\begingroup\$ @MarcusMüller user has not specified any Diode current, so it is hard to assume anything. Carlos, please tell me how much current you need in output. \$\endgroup\$
    – Deepak
    Commented Oct 6, 2020 at 8:56
  • \$\begingroup\$ Thank you @MarcusMüller, I don't know the Amps required yet, but I will consider it at 50% of max as you mentioned... that is a perfect example of the "parameters" I was talking about in my question, that I did not know that should be considered \$\endgroup\$ Commented Oct 6, 2020 at 12:55
  • \$\begingroup\$ @CarlosGarcia you need to know the amps before you even start choosing a power supply, so I'll directly send you back to your design state: Define this most crucial design parameter before asking about whether you can use some specific supply. You're approaching the problem from the wrong end! \$\endgroup\$ Commented Oct 6, 2020 at 15:13

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