Universal dimmer

[aaronik19]

Hi friends,

I tried to google but i think that i am using the wrong keywords. Do someone has any universal dimmer circuit of from where i can buy universal dimming kit to dimm by PIC?

Thanks

[Ttelmah]

There is no such thing as a 'universal dimmer'. Different types of loads need different control. Different power, different size modules, etc. etc..

However there are a large number of X10 dimmer modules, and X10 can easily be generated by a PIC. There is a driver with the compiler.

Use a commercial interface module for safety, and choose a dimmer to suit the type and power of your load.

[gpsmikey]

X-10 is one option. Basically a "dimmer" for AC (DC is done somewhat different, but same sort of idea) is done with a zero crossing detector then triggering the triac at some time after the zero crossing during the half cycle. Unless you are very familiar with working with mains power though, do NOT experiment - you may manage to let the "magic smoke" out of either your circuit or more importantly, yourself. Mains voltages can be fatal if you don't know what you are doing.

mikey
_________________
mikey
-- you can't have too many gadgets or too much disk space !
old engineering saying: 1+1 = 3 for sufficiently large values of 1 or small values of 3

[Ttelmah]

As a separate suggestion, look at:

<http://www.controlanything.com/Relay/Relay/SERIAL_LIGHT_DIMMER>

This is as near to safe as you can get (all pre built, with proper plug connections for the output devices). Simple RS232 commands.

Best Wishes

[aaronik19]

thanks all for your reply. I used to work on Intelligence system so I have good experience on AC. Thanks for your thoughts.

Just to get a better design, I have a question. When using a TRIAC design, to fire the triac, what is the best technique? Using PWM?

[Mike Walne]

[Ttelmah]

One think I'd say about 'using TRIAC designs'. Don't!...

Realistically the TRIAC, is a very simple way of making a crude light dimming circuit. However it's 'simplicity' tends to disappear in modern applications. It is so easy to make circuits with a TRIAC, that produce a lot of RF noise, and relatively difficult to make ones that don't. By the time you add the components to keep RF acceptable, the 'simplicity' of the TRIAC disappears. With the tightening of RF regulations over the last few years. there is a steady move away from TRIAC designs.
Historically if you look at simple house light dimmer switches, twenty years ago, all were TRIAC based. Now hardly any are. You will see SCR dimmers as being much more common, and even in some cases IGBT based units.
SCR's are almost as noisy as TRIAC's - but not quite so bad, and can handle much higher currents. The difference is because the TRIAC is inherently not perfectly symmetrical, resulting in imbalance in the half cycles, and making more noise. IGBT based designs, use a MOSFET as the switching element, and are commonly 'trailing edge' dimmers.

On all phase dimming solutions, 'no' you wouldn't use PWM.
What you use is the CCP. You have hardware to detect the zero crossing point of the waveform. You use this to reset the counter feeding the CCP, and load the CCP with the count corresponding to when you want the trigger the gate. Then at the designed interval 'after' this, you send a single trigger pulse to the gate of the control device (thyristor or triac). The device then remains 'on' till the next zero crossing point. The CCP allows you to generate an interrupt when a count reaches a particular value, and this is ideal as the way of generating the pulse.

On trailing edge dimmers, instead of turning the power 'on' half way through the cycle, and then off when the waveform next reaches zero, you turn the power 'on' at the zero crossing point of the mains cycle, and then turn it _off_ when desired. Key is that the voltage being fed to the device always comes 'on' at the nice slow rate from the mains cycle, not being thumped on by an electronic switch. Result less thermal shock to the filament, less problems with electronic circuits, etc. etc..

Best Wishes

[aaronik19]

this is why I mentioned pwm last time. I found the following circuit which is an alternative to traditional dimmers.

http://www.eleccircuit.com/wp-content/uploads/2010/08/dimmer-with-a-mosfet-circuit-diagram.gif

can I use the same method used on Triacs instead of using PWM?

[gpsmikey]

That is one approach, however, the first consideration is the PWM must be somehow synchronized to the mains frequency (or very different from it) unless you want strange strobing effects from the beat frequency. That also only applies mostly to a resistive lamp load - you asked about "universal" which would also include fluorescent, LED or transformer type halogen etc (all common lighting circuits). That is why there are currently many different types of dimmers out there - each one has some advantages and disadvantages. You need to narrow down just what you are "dimming" and evaluate what the options are as far as the different types. Some are better as far as RFI goes, some are better from a cost standpoint, some have the advantage (like with a micro) of being able to remote control the dimmer.

mikey
_________________
mikey
-- you can't have too many gadgets or too much disk space !
old engineering saying: 1+1 = 3 for sufficiently large values of 1 or small values of 3

[Ttelmah]

That circuit would work for something like a fish tank heater - large thermal inertia, so won't care about 'flicker' problems. With a PWM at a reasonably high frequency, it would work for simple incandescent lamps. It wouldn't really work for a TRIAC without synchronisation as gpsmikey says. Things like electronic circuits (most modern lights...) generally _require_ trailing edge dimming (many things that say they are 'compatible' with dimmers will only work with trailing edge designs).
The nature of the load 'matters'. What current?. Lamp. heater, etc. etc?.. Does it include electronics?.
There is no 'universal' solution.

Best Wishes

[aaronik19]

I used to work with Legrand authorised seller and i was sure that there is an Universal dimmer. By term universal it means that it can handles a wide range of different loads such as halogens, incandescent, PL lamps etc...

Kindly visit the link below. Legrand have a good range of dimmers...

http://news.thomasnet.com/fullstory/Universal-Dimmer-eliminates-lamp-flickering-20010786

[aaronik19]

By sync, you are meaning to use zero crossing to have the right reference?

[Ttelmah]

A trailing edge MOSFET dimmer, is the closest you can get to a universal dimmer. It'll work with electronics that supports dimming, and with resistive/lighting loads. Needs to be synchronised, and going 'on' at the zero crossing point, then off as needed. Can't be done with a TRIAC design, or SCR design (except GTO parts).

[aaronik19]

Hi ttelmah thanks for your feedback. I tried to look for such circuit long time ago but found nothing. Do someone has any circuit?

[asmboy]

Typically this is done by placing a suitable mosfet inside a full wave (4 diode) bridge- with the ac passing THROUGH the back-2-front arms of said diode bridge. Mosfet gate optical isolated control is how you turn it on and off.

Also resistive loads produce MUCH less RFI than reactive items like motors.