Control4 Develops IP-Based Hardwired Lighting Control System

Does this FET approach reduce the amount of noise and hash emitted over the power lines compared to what the triggering of the TRIACs emits?

  =D-

Derek R. Flickinger
Interactive Homes, Inc.

The short answer is yes.  FETs emit less RF noise in generall, not only on the power lines, but throught the air also.

For the long answer of why one might use a reverse phase (MOSFET or IGBT) style dimmer vs. the forward phase (Triac) dimmer, read on.

Cautionary note: This next section is only for uber geeks.

Triac Dimmer:
Compatible load types include Incandescent, Halogen and Magnetic/Inductive loads such as MLV and motors. Resistive and Inductive.

Benefits are, easy to produce due to the use of a single load controlling semiconductor, low cost and ease of design.

Drawbacks are, regulatory approval due to high EMI, high inrush current and load incompatibility with capacitive load types such as Electric Ballasts and LED converters.
          A Triac is a bilateral semiconductor switch whose turn on time is uncontrollable. Because of this fact the triac presents a very high rate of change in voltage to a given load over a very short period of time. Typically for resistive loads such as Incandescent or halogen this does not present a problem although one could argue that this continuous bombardment from the triac does cause undesired noise from the filament and may even reduce the life of the bulb over time. It is a known fact that these high dv/dt pulses cause undesired and hard to control electromagnetic energy that is feed back onto the AC lines. Using external components to control this unwanted energy adds complexity and cost to the design as well as producing unwanted audible noise from the dimming device.

          The even bigger problem has to do with inrush current that is present during the switch on time for each phase of the AC signal. If this signal is presented to a load that contains a capacitive electronic ballast, inrush currents in the 100’s of amps can result. This can cause unwanted noise in the ballast and can cause premature failure of the components in the ballast.  Some Electronic Ballasts are made to be low capacitance to reduce this effect but, as you increase the number of loads on a dimmer eventually the capacitance increases only to produce the problem again.

Reverse phase dimmer:
Compatible load types are Incandescent, Halogen, Electronic Low Voltage and LED. Resistive and Capacitive.

This technology provides benefits when controlling loads with capacitive characteristics such as Electronic Low Voltage and LED lighting. The leading edge sinusoidal waveforms produced from this type of dimmer make it more suitable for driving capacitive load types that are less tolerant of high inrush currents. This produces less noise and has far less harmonics than those produces from the rapid on switching of the Triac. This results in far less electromagnetic energy from these harmonics and much better load compatibility.

One drawback to reverse phase dimmers are not compatible with inductive loads. This is true for two reasons. While it is very easy to control how fast and when a MOSFET or IGBT turns on it is not easy to control how fast they trun off. This effectively can result in asymmetric waveforms that result in DC currents being present at the primary of the inductive element. This, can overheat and destroy the magnetic ballast.

<<Cautionary note: This next section is only for uber geeks.>>

Derek, you’ve met your match.

I am confused.  Are we actually then talking about MOSFETs or plain old FETs.  They are two different things, which is one reason I asked the original question.  One normally would think of MOSFETs as output transistors for audio amplifiers, not something for higher current lighting devices.

While the logic is valid for why this is a positive introduction into the medium voltage marketplace, there must be some drawbacks - or others would have implemented this approach a long time ago.  This sounds like God’s gift to the world of incandescent, LED, inductive, and fluorescent lighting control, but, while I think on paper it is great, what are the gotchas?

  =D-

The best AC dimmer design would be one that simply lowers the overall voltage level going to the controlled load rather than “clipping” the wave.  Since there is really no reasonable way to do this we have to settle for the clipping approach.

And the real answer to the God’s gift comment is that many already have used this approach.  This is just the first product from Control4 to use this approach.

Thanks Eric.  We just wanted to get a little more detail than what Julie had in the article.  They sound great.

Are you using any “standards-based” interfaces for control and status monitoring of the devices via the Ethernet connection?  Are your commands sets using something like the UPnP Home Automation DCPs for lighting devices or are they based upon the Lighting Control Automation Profile from ZigBee (since that is what Control4 is using elsewhere)?

Thanks,

  =D-