So my dad found one of these voltage converters lying around.

I was quite curious what components it had as it is very lightweight (transformerless) and boasts a good 1600W @ 110vac (14.5A) on the output.

I've included a very rough schematic I drew out:

enter image description here

The two circled components are the ones I'm having trouble identifying.

The first component on first glance appears to be a zener diode, however it only has a single mark in the middle and no mark on either side (hence my confusion)

The second (at the top of the schematic) measured 220ohms across it. Is this just a very high watt resistor or does it serve another purpose? It appears to just be a block of carbon.

I'm very curious also if this circuit can actually handle the 1600W it states. I know the triac is rated for 15A (with a very sizable heat sink) but it's the other components that trouble me. Also what kind of power supply is this? A capacitor supply? I thought most of these would only handle a few hundred mA.

First post here so thanks for any responses in advance.

  • 1
    \$\begingroup\$ fwiw I think the carbon like component is a thermal device that keeps the triac off if it is too hot. \$\endgroup\$ Commented May 21, 2017 at 15:07
  • \$\begingroup\$ @VladimirCravero Of course, that would make sense. Thanks for your input. \$\endgroup\$ Commented May 21, 2017 at 15:52
  • \$\begingroup\$ I'm assuming you measured the components out of circuit? \$\endgroup\$
    – uint128_t
    Commented May 21, 2017 at 17:00
  • \$\begingroup\$ I would hesitate to call this thing a "power supply"; it's essentially a fixed-position dimmer. This is also why it says it's for heating appliances; purely resistive loads that work well with phase-cutting dimming. The small glass component is likely a diac, a diode-like component that's frequently used in simple dimmers. \$\endgroup\$
    – marcelm
    Commented May 21, 2017 at 17:30
  • \$\begingroup\$ @marcelm Oooh, I think you're right about the diac. I'll add a diac in my simulation and see what happens. \$\endgroup\$
    – uint128_t
    Commented May 21, 2017 at 17:36

1 Answer 1


By no means an expert in this sort of design, but I think I figured it out...

Notice that all of the loads it says may be used are resistive (at least, primarily e.g. hairdryers are a big resistive element with a relatively small fan). Hence, the circuit doesn't actually have to convert the 220V to 120V, it just has to scale down the total power. Consequently, a half-wave rectifier isn't a bad choice. This circuit is essentially an active half-wave rectifier. It is somewhat apparent from careful inspection, and confirmed by a crude simulation.

I assumed the diode to be a bog-standard 1N4148, because that's what it looks like. Per marcelm's comment, it's more likely to be a diac, although replacing it with a diac model in simulation didn't change anything. I agree with Vladimir that the carbon-like thing is some sort of temperature cutout circuit, although my simulation doesn't seem to confirm that...

Anyway, here's your schematic, redrawn. I had to use an equivalent circuit for the triac because I couldn't find a working triac model. Note that Vbe of Q1 goes to -600V, so either it's a special transistor or the schematic is not quite right.

enter image description here

Here's the voltage across the load. There are still things to adjust in this schematic, but it's close.

enter image description here

While this simulation may not be entirely correct, I think you can get the gist of the circuit: it's not linearly reducing voltage, it's simply switching on the line voltage some of the time. As such, the output is not sinusoidal, hence why it is only specified for use with resistive loads. That is also why it is able to handle 1600W: the triac, conducting the load current, is either on or off, and is therefore quite efficient. The other components are merely for control, and handle very little power; the only component in series with the load is the triac, therefore it's the only thing that needs to be "beefy". The other components need to handle high voltages, yes, but not very much power.

  • \$\begingroup\$ Wow. Above and beyond, I must say. Thank you for your kind work. It's much appreciated. \$\endgroup\$ Commented May 21, 2017 at 18:24

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