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# Dimmer through mosfet?

P

#### [email protected]

Jan 1, 1970
0
Would a construction like this:

220V AC --> Fullwave rectifier --> Capacitor --> 1xPowerFet --> Capacitor -->
Resistive load (bulbs, heaters)

PowerFet/Mosfet etc.. feeded with pwm pulse.

Be able to get significantly reduced RF emissions than standard tyristor style
dimmers ?

Computer control is planned.

B

#### Ban

Jan 1, 1970
0
Would a construction like this:

220V AC --> Fullwave rectifier --> Capacitor --> 1xPowerFet -->
Capacitor --> Resistive load (bulbs, heaters)

PowerFet/Mosfet etc.. feeded with pwm pulse.

Be able to get significantly reduced RF emissions than standard
tyristor style dimmers ?

Computer control is planned.

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.

A

Jan 1, 1970
0
Would a construction like this:

220V AC --> Fullwave rectifier --> Capacitor --> 1xPowerFet --> Capacitor -->
Resistive load (bulbs, heaters)

PowerFet/Mosfet etc.. feeded with pwm pulse.

Be able to get significantly reduced RF emissions than standard tyristor style
dimmers ?

Computer control is planned.

Hmm sine wave and reverse phase control dimmers dimmers like:

http://www.ies.nl/

http://www.etdimming.com/capio_press.asp

http://www.compulite.com/ look for Compusine

bit more

http://www.tvtechnology.com/features/let-there-belighting/f_ac_let_there_be_lighting-07.09.03.shtml

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.

A

Jan 1, 1970
0
Ban said:
Standard dimmers use triacs, not thyristors.

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.

y

C

#### CFoley1064

Jan 1, 1970
0
Subject: Dimmer through mosfet?
From: [email protected]
Date: 10/3/2004 9:31 PM Central Daylight Time
Message-id: <[email protected]>

Would a construction like this:

220V AC --> Fullwave rectifier --> Capacitor --> 1xPowerFet --> Capacitor -->
Resistive load (bulbs, heaters)

PowerFet/Mosfet etc.. feeded with pwm pulse.

Be able to get significantly reduced RF emissions than standard tyristor
style
dimmers ?

Computer control is planned.

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.

http://www.fairchildsemi.com/an/AN/AN-3003.pdf

Good luck and play safe
Chris

P

#### [email protected]

Jan 1, 1970
0
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.

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

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

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.

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.

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))).

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.

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?

C

#### CFoley1064

Jan 1, 1970
0
Subject: Re: Dimmer through mosfet?
From: [email protected]
Date: 10/4/2004 8:44 AM Central Daylight Time
Message-id: <[email protected]>

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

kind

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 www.tech-chat.de 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. http://www.jameco.com/webapp/wcs/stores/servlet/CategoryDisplay?storeId=10 001&catalogId=10001&langId=-1&categoryId=11364 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.

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&s
toreId=10001&catalogId=10001&productId=136747

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

C

#### CFoley1064

Jan 1, 1970
0
Subject: Re: Dimmer through mosfet?
From: [email protected]
Date: 10/4/2004 8:44 AM Central Daylight Time
Message-id: <[email protected]>

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

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

P

#### [email protected]

Jan 1, 1970
0
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

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.
(http://www.strandlighting.com/PDF/Sinewave Dimmer Technology.pdf)
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

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

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).

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.

P

#### [email protected]

Jan 1, 1970
0
Some further reading pointed me in the direction of IBGT. One approach is
to
the line
Wouldnt reccomend this unless your total load is fairly low, not a common
way of doing things.

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

Sinewave pwm is noisy?
Ive built a few dimmers , repaired ,er, a few, dinnae re-invent
wheel.Building things aint rocket science but cost isnt discrete
components, its the hardware, box , heatsinks, wiring , fuses holders
connectors etc etc.

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

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..

A

Jan 1, 1970
0
Sinewave pwm is noisy?

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

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.

P

#### [email protected]

Jan 1, 1970
0
Nope refering to normal phase control, sinewave dimmers are virtually
silent.

Any suggestions on filter?
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.

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.

A

Jan 1, 1970
0
Any suggestions on filter?

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

Could always go scouring through U.S. patents www.uspto.gov it has the full
published patents online.
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.

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.

P

#### [email protected]

Jan 1, 1970
0
Nope refering to normal phase control, sinewave dimmers are virtually
Bigger chokes, per channel, slow the rise time as it bangs on, is generally

Chokes as in inductance in series with the ac input?
whats used , and x y y capcitors in a delta formation across the output,
though these can cause nuisance tripping on earth leakage protection.

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.)
Could always go scouring through U.S. patents www.uspto.gov it has the full
published patents online.

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

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 $$I hope. =) A #### Adam Aglionby Jan 1, 1970 0 generally Chokes as in inductance in series with the ac input? Per channel , yes http://sound.westhost.com/project62c.htm has typical output channel What about not connecting the earth to the switching part, only let it through to the load. And especially what if neither ac source nor load has earth? (as to avoid any earth leakage circuits activation) Motor suppressors use a dlta form of Y rated , live to earth and X rated Live to Neutral to try and dumop some of ythe chash. At 220/240V unless its double insulated you definately want anything metal eathed. (As a sidenote, in .se 4-wire system is used (PEN-wire). And 5-wire system is done through connecting neutral to ground in the central fuse box.) I don't live in US, and I won't massproduce it so I think it's a non issue. Not to get a patent but to look at what has bee patented to get some ideas from. well. Well management can make bad decisions stay around a long time.. It was a technical thing , sure Sony released and withdrew a ClassD car amp because of unrelibailty in field. Any ideas concering active power factor correction circuits? I'm thinking on the case I would later like to apply the ibgt-sinewave stuff to a inductive load.. either DC motors, or AC->DC->Inverted for AC motors. Motor drives is a whole big subject that would be better asking someonelse about. Btw.. I'm thinking on how to use the ibgt-sinewave technique to make DC 12V -> AC 240V.. could produce sinewave for less$$ I hope. =)

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.

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