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So my stupid room is wired so all of the lower receptacles are driven from the electronic wall dimmer. Stupid me plugged in my brand spanking new brother laser printer into the lower receptacle. It was working fine, other than a bit of a buzz coming from its power supply. I didn't realize this until about a day later, after it finally hit me why my printer may be doing a self test every time i turn on the lights in my room. doh! I plugged the printer into the correct receptacle. It still works ok. Could its lifetime be shortened by this short stint of triac-supplied power? I imagine the printer of course has a switching power supply, which clearly was not fazed by the chopped up waveform. I imagine this is the same scenario as a PC power supply would see when connected to a standard UPS without a pure sine inverter. However I'm not sure about other parts of the laser that are not on the DC supply, such as the fuser, etc. I did run off a couple pages while it was plugged into the dimmer. Anyone care to weigh in on this?

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The input of a line-powered SMPS is usually designed for AC (sinusoidal) voltages of a certain frequency. There are some with a specification of a DC input, and except for compact fluorescent lamps (CFLs), I know of exactly zero with a specification for an AC input with chopped-off edges (phase-angle control as offered by a dimmer). There are reasons...

Two examples why running a SMPS off a dimmer is not the best idea:

  1. As long as the load doesn't change, A SMPS usually operates at a constant power. As you decrease the input voltage with your dimmer, the V*I product is kept constant, and the current increases, causing more heat in many components of the SMPS's primary. A well designed switcher will become warmer, but survive for a bit at the cost of a shortened lifetime. A cheapo switcher may fail because it may never have been tested exhaustively below its minimum specified input voltage.

  2. The waveform of the input current (not: voltage) will not look like what the SMPS's designers expected when you use a dimmer. If it's a simple full-bridge rectifier, current spikes beyond the design specifications may occur. If it's a power factor correction (PFC) input, the SMPS will try to draw a sinusoidal, in-phase voltage and current waveform and will be confused big time when you offer a sine wave with cut-off edges, using a dimmer.

As seen from the dimmer, well, that guy won't be happy either...

After this long intro: If your printer still works, and there was no bad smell, I believe it's still good and you probably won't notice a shortened lifetime - you don't sound like you were doing this for years before noticing...

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Most typical SMPS (switch mode power supply) should be totally fine with under voltage or chopped up input. When the input voltage or current is below what is required they simply shuts down or fail to start

One of the big design wins with a SMPS is that there is very little relationship between input voltage and waveform, and out voltage and waveform. So this generally protects sensitive electronic circuitry for all manner of bad input into the SMPS

Most devices (including laser printers) generate any high voltages they need from after the SMPS too, so these should not be a problem either. This is to make the high voltage controllable and the device useful around the world on the different global voltages

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    \$\begingroup\$ Right, I'm guessing that this printer has certain requirements outside what the SMPS can supply, because its spec sheet states for voltage: AC 120V 50/60Hz. It seems to be working ok for now... I'll take a guess that the fuser is some type of resistive heating element so it would be just fine if exposed to the dimmer current directly (maybe it won't get quite as hot when the dimmer is down low?). They probably specify 110-120v only because on 220-240v I bet it would get way too hot. I guess the rest of the IC's, small motors etc are supplied power by the SMPS so are ok too. \$\endgroup\$ – user1304223 Dec 29 '12 at 8:36

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