Some professional dimmers use a inverter to generate higher frequencies for the AC drive for the lamp. Then burst mode control is possible, but as you say I have certainly never seen a commercial dimmer using burst mode.
Cheers
Klaus
In addition to flicker, half-cycle switching sometimes can cause audible vibration of the filament and its supports, very irritating when it occurs.
Cheap dimmers often do not filter RFI very well, and can be a major source of interference to X10 communication when the switching point falls within the signaling interval.
-- Jim McGinnis
Yes, but:
1) That implies not using a clock tick interrupt, but a simple infinite loop instead. That can lead to difficulties when, say, reading commands from a serial port, since that inevitably leads to timing irregularities that ca cause noticeable flickering.2) On many MCUs, a "decrement and skip" or similar is a single instruction, while a compare requires a subtraction followed by a conditional test - two instructions. On a PIC (14-bit), for instance, the tick code for 3 lamps would look something like:
movlw b'111 decfsz phase0 andlw b'110 decfsz phase1 andlw b'101 decfsz phase0 andlw b'011 movwf portb
-- Max
I don't think you could see flicker at 10% power and an eye test has nothing to do with it. Try it and you will see what I mean. Or just give it some thought.
On 6 6 6 5 6 6 6 5 Off 6 6 6 6 6 6 6
I have never seen a cheap dimmer that did not generate RFI. I checked some references on the web and they indicate that RFI can be a problem. There are also issues with harmonics that affect the power input.
-- Rick "rickman" Collins rick.collins@XYarius.com Ignore the reply address. To email me use the above address with the XY removed. Arius - A Signal Processing Solutions Company Specializing in DSP and FPGA design URL http://www.arius.com 4 King Ave 301-682-7772 Voice Frederick, MD 21701-3110 301-682-7666 FAX
My understanding is that this can happen with partial wave dimming as well as the chokes that are used.
-- Rick "rickman" Collins rick.collins@XYarius.com Ignore the reply address. To email me use the above address with the XY removed. Arius - A Signal Processing Solutions Company Specializing in DSP and FPGA design URL http://www.arius.com 4 King Ave 301-682-7772 Voice Frederick, MD 21701-3110 301-682-7666 FAX
Doh! Should be: decfsz phase2
-- Max
The flicker fusion frequency varies greatly depending on the individual, surrounding lighting and other factors. Peripheral vision is more sensitive than central vision, and fatigue may increase flicker perception. Even when flicker is not consciously perceived it can have measurable negative effects.
-- Jim McGinnis
You still have not considered the whole problem. I can guarantee that no one will see flicker when a 100 Watt bulb is fed 10 Watts of power and they will not suffer any negative effects, regardless of the frequency.
-- Rick "rickman" Collins rick.collins@XYarius.com Ignore the reply address. To email me use the above address with the XY removed. Arius - A Signal Processing Solutions Company Specializing in DSP and FPGA design URL http://www.arius.com 4 King Ave 301-682-7772 Voice Frederick, MD 21701-3110 301-682-7666 FAX
Interesting document - you should read the part beginning "Other not so good ideas for dimming".
-- Jim McGinnis
I assume you're implying that 10% power would result in no light output - just heat. While that's probably true of the average domestic lamp (particularly if only being fed from a feeble 115Vrms), it certainly isn't true for other lamp types with low thermal mass and higher efficiency. I have actually tried feeding 1 in 10 half-cycles to a 2500W CP91 lamp (bog-standard for stage lighting in most West-End theatres) as a possible method of pre-heating. The lamp gave significant light ouput, with very clear flicker at up to about 14Hz or so (1/7 @ 100Hz, 230V). I measured the efficiency at only about 4% IIRC, as compared to the 20% or so at full power, but a mere 0.4% of the full light output of a lamp like that is still a lot of lux, especially in a darkened theatre!
Will result in noticeable flicker with precision lamp types, particularly at higher power levels.
Oh, and this technique is liable to generate quite large DC components in the feed if you're not very careful, which should trip all the breakers in any professional installation. Trying to keep a 3-phase supply anywhere near balanced would be an absolute nightmare.
I'd say that's simply a problem of inadequate legislation where you live. European EMC regulations just don't allow the really cheap and nasty designs onto the market.
RFI is only a problem if you don't design it out. One ferrite and a couple of caps is really all that's needed for a domestic dimmer.
Dimmer packs for serious applications inevitably provide power-factor correction, which solves that issue.
-- Max
... snip ...
Reset it to what? What delays ensued between the arrival at zero and the actual handling in the interrupt? Most counter systems can be set up to self recycle, while raising an interrupt, so that no errors accumulate. Even adding a delta value to the present content has various possibilities of error. I have been bitten by this sort of thing long long ago, and found means of avoidance.
--
Chuck F (cbfalconer@yahoo.com) (cbfalconer@worldnet.att.net)
Available for consulting/temporary embedded and systems.
USE worldnet address!
I did. "unless the dimmer-driver can do some sort of dithering to spread out the flicker spectrum". Wouldn't that be simple for an MCU?
-- Rick "rickman" Collins rick.collins@XYarius.com Ignore the reply address. To email me use the above address with the XY removed. Arius - A Signal Processing Solutions Company Specializing in DSP and FPGA design URL http://www.arius.com 4 King Ave 301-682-7772 Voice Frederick, MD 21701-3110 301-682-7666 FAX
How would I know? The problem statement is a little skimpy on details...
Again, details are missing...
On this one, I'd presume the latency to be nearly constant, whatever it is.
What errors can accumulate when synched to the power line? You're starting anew with each cycle or half-cycle.
Like the RTC on PC's?
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.