Dimmer through mosfet?

Don't they have 230V AC in Sweden, as in the rest of Europe? EMI problems will be significantly worse with the setup you desribe, as you have to switch much faster with the PWM, the capacitors won't help much either, what you need are inductors. Standard dimmers use triacs, not thyristors.

RFI is caused by di/dt rather than switching element itself -- to reduce the effect, good lamp dimmers will typically add a small (20 to 30 uH) high current toroidal choke in series with the lamp load to soften turn-on.

It's potentially hazardous to rectify line voltage and expect to control it with a computer without an optocoupler somewhere in your control chain. I kind of get a feeling the reason why you're doing this is that you feel comfortable with switching FETs and you don't know too much about TRIACs and thyristors. The best way to do the job you're describing is with standard TRIACs and optocouplers, if for no other reason than having a current path between hazardous voltages and a computer is asking for disaster.

Take a look at Fairchild App Note AN-3003, Applications of Non Zero Crossing Triac Drivers Featuring the MOC3011. Since you're controlling 220VAC, you'll need to use a MOC3051/3052 instead of a MOC3011.

Good luck and play safe Chris

Capacitor -->

style

Hmm sine wave and reverse phase control dimmers dimmers like:

bit more

Guess some of this technology comes from AC motor drives, but the very few manufacturers who make them kind of indicates that it seems close to rocket science.

Adam

SCRs tend to be a bit more resiliant to a big lamp blowing on them where triacs can blow before the breaker trips, lot of older and big expensive installation dimmers still use thyristor or solid state relay with SCR (thyristor) outputs.

Adam y

Any tip on a semiconductor that can turn on the load in each phase with a slower di/dt without becomeing an electrical heater :) ..?

Optocoupler is so natural for me safe-wise that I didn't put it in the generic schematic. When working with dangerous voltages I always check things twice, and make sure all parts are properly fastened at safe distance from eachother. And analyze what happens should a component fail, or if thunder, spikes etc.. would occour.

I know very well about triacs, my idea was to find an alternative that will avoid emitting RFI. Maybe generating pulsed sinewave with a mosfet would be better?, as the di/dt might then be lower (U=220*abs(sin(w))).

Nice chip.. now the thing is to get it ;)

Btw, is it feasable to modify an of the shelf dimmer by replaceing the dial with a transistor-optocoupler in some way?

The key to reducing RFI from dimmer switching is to just take the edge off the very fast transistion from no current to full current, particularly when dealing with cold light bulbs, which grab a lot more current than ones that are already on. A small choke will do this well. There are many chokes, both toroidal and non-toroidal, which are made for this application. Another thing is, you only need one for all the triacs -- just put it in series with the line before your loads like this (view in fixed font or M$ Notepad):

L1 ___ o----UUU------o-------o-------o-------o------------. | | | | | | | | | | ,---. ,---. ,---. ,---. ,---. | X | | X | | X | | X | . . . | X | '---' '---' '---' '---' '---' | | | | | _|_ _|_ _|_ _|_ _|_ V_A V_A V_A V_A V_A / | / | / | / | / | | | | | | | | | | | L2 | | | | | o-------------o-------o-------o-------o------------' created by Andy´s ASCII-Circuit v1.24.140803 Beta

All the opto stuff has been assumed here.

You can get a 10uH 11A choke for $3.99 and a 25uH 5.5A choke for the same price from Jameco:

Jameco #: 208266 25uH, 5.5A Jameco #: 208258 10uH, 11A $3.99 USD ea.

If you have enough current to require the 10uH chokes, you might want to put two in series if 10uH is still giving you too much RFI. The easiest way to tell is to get an old AM transistor radio, and dial over the frequency range while your dimmer circuit is working. If you can't hear the buzz when your dimmer is working, you're probably OK. Try various antenna positions and orientations, as well as different power settings on your dimmer.

Looking at MOSFETs for this is probably the wrong direction. A fast switching MOSFET which would give you a simulated sine wave would have many more opportunities per line cycle to generate current pulses which would cause RFI. The above is the simplest, easiest way to do this. Also, the thermal constant of light bulbs and heaters is such that you won't gain anything by using high frequency PWM for voltage control.

Is it possible you're concerned about finding the zero crossing? If you're looking at using computer control for TRIAC phase control, all you need is a way to mark the line voltage zero crossings, and then knowing if you've got 50 Hz (10 ms) or 60 Hz (8.3 ms), you can time out to where you want to turn on the TRIAC. Most people use the low voltage AC coming off the power transformer for the computer power supply to generate the zero crossing interrupts. If you're using a PC, you will need a separate transformer, as well as a way to get the interrupt into the PC (I'd try using assembler/C and one of the status pins on the printer port to generate interrupt, if you don't have a separate card for this).

The MOC3051 is available at Jameco as their #: 277860 for $0.74 ea.

Good luck with your project. Try the TRIAC/opto setup. It's what everyone else does, it's more efficient, costs less, and it's really what it's made for.

Chris

Nope. Most "off-the-shelf" dimmers operate on a principle of charging an RC delay with line voltage, and using a DIAC or other SBS (silicon bidirectional switch) to discharge the C once it reaches a threshold voltage. If you know the zero-crossing point and can use an optocoupler that will source enough current to turn the triac on, you can replace the potentiometer, a couple of Rs, the C, and the DIAC. But in that case, why not just make it yourself?

Good luck Chris

Some further reading pointed me in the direction of IBGT. One approach is to let it conduct at the beginning of the sinewave. And then shutoff when desired power has been reached (area under the graph..). Another method is to let the ibgt gate be pwm modulated with a few tens of kHz and by varying the duty cycle. Put together a sinewave through a series of pulses with varied duty cycle. The addition of a capacitor or similar will then smooth it to a near perfect sinewave.

Won't the wire between dimmer and load radiate RFI, as most power cables don't have foil, or twists..?

I prefer if the unit takes care of zero crossing etc.. by itself. A simple PIC 12Fxxx could do the job. Being fed what to do over some multidrop arrangement. With a central computer doing the intrisics there might be problem if the computer is on another phase than the dimmer+load. Or there's a software crash.

off the

that are

to

desired

series

will

both

thing

the line

Wouldn`t reccomend this unless your total load is fairly low, not a common way of doing things.

don't

Er, um, hence some of the marketing speil about sine and reverse phase dimmers, phase chopping dimmers are noisy, big chokes , slower rise time, good.

crash.

I`ve built a few dimmers , repaired ,er, a few, dinnae re-invent wheel.Building things ain`t rocket science but cost isn`t discrete components, its the hardware, box , heatsinks, wiring , fuses holders connectors etc etc.

Analogue 0-10V control used to be thing, now DMX 512 is the control standard for stage lighting:

seems to be down at mo, great starting place:

Just use your computer as the desk and have the dimmers seperately. Someone like Thomann

has DMX dimmers by someone like Showtec or Botex, Soundlab ones are too poor would avoid, for frankly less than you can build them., if your determined to build your own dimmers stick with DMX

There are a few DMX freeware Dongles about:

HTH Adam

Sinewave pwm is bad? I thought the smaller surges would be easier to filter out.

Sinewave pwm is noisy?

I know :) What I would like to achive is not a cost reduction per se. But a reduction of RFI compared to forward/reverse phase dimmers.

Well I don't mind ethernet/usb, as latency won't be an issue for me. Infact a IR link from the computer to the devices would be useful to eliminate the need for wires, radiolinks, x10 etc..

cables

Nope refering to normal phase control, sinewave dimmers are virtually silent.

reduction of

Reverse phase dimmers are quieter as well because theyre switching off rather than on. But the few manufacturers in the arena do indicate there is difficulties with sine and reverse phase dimmers, not sure what, but at least one manufacturer showed a prototype at a trade show couple of years back and have still to release a production version.

Adam

Any suggestions on filter?

I read somewhere that it might have to do with some patent.... Ofcourse if could be some purely technical issue.

Reverse phase dimmers is an improvement. I think sinewave pwm is the best (now) so I will try that route. Althought I think I will do some basic testing first to see if the concept works at all.

Bigger chokes, per channel, slow the rise time as it bangs on, is generally whats used , and x y y capcitors in a delta formation across the output, though these can cause nuisance tripping on earth leakage protection.

Could always go scouring through U.S. patents

(now)

first

The concept works , because people are making them , but not very many are making them including some top end dimmer makers.

Mebbe looking at Class D amplification might give some insight because it seemed to take ages before anyone got that to work outside the lab as well.

Remeber to let us know how your getting on.

Adam

Chokes as in inductance in series with the ac input?

What about not connecting the earth to the switching part, only let it through to the load. And especially what if neither ac source nor load has earth? (as to avoid any earth leakage circuits activation)

(As a sidenote, in .se 4-wire system is used (PEN-wire). And 5-wire system is done through connecting neutral to ground in the central fuse box.)

I don't live in US, and I won't massproduce it so I think it's a non issue. ;)

Well management can make bad decisions stay around a long time..

Any ideas concering active power factor correction circuits? I'm thinking on the case I would later like to apply the ibgt-sinewave stuff to a inductive load.. either DC motors, or AC->DC->Inverted for AC motors.

Btw.. I'm thinking on how to use the ibgt-sinewave technique to make DC 12V -> AC 240V.. could produce sinewave for less $$ I hope. =)

generally

Per channel , yes

has typical output channel

through

Motor suppressors use a dlta form of Y rated , live to earth and X rated Live to Neutral to try and dumop some of ythe chash. At 220/240V unless its double insulated you definately want anything metal eathed.

is

full

issue. ;)

Not to get a patent but to look at what has bee patented to get some ideas from.

are

well.

It was a technical thing , sure Sony released and withdrew a ClassD car amp because of unrelibailty in field.

stuff

Motor drives is a whole big subject that would be better asking someonelse about.

Seen some cheap, `true sine` inverters about, in addition to the `quasi sine` 2 step square wave about, usual far eastern stuff , buy one and pull the lid off.

Adam