Recently I've started creating my own lighting control system and I had to read through a lot of papers about dimmers. Unfortunately it occurred that information form advertising text from shop sited does not match information from electronics engineers forums and articles written by specialists. As far as amount of adverts is much greater it is not easy to find out the truth.
Warning. To write this post I've used source in Russian language. I don't have ability to search for English analogs of that sources nor I want to overload this post with a lot of additional information from that sources. If you know good sources on English language let me know please.
All modern dimmers use phase modulation to control brightness. Convenient dimmers wok in one of two modes: they can cut off front of the wave or they can cut off end of the wave. Depending on that dimmers are called C or L (CR or LR). C means capacitance and L means inductiveness. R is resistance, but resistive loads can be safely attached to any type of dimmer. You can find pictures and description here
. In may articles you would read that symistor (triac) dimmers all have L type and transistor dimmers all have C type. Actually, with transistor you can cut any part of the wave. So you should look at markp, not on type of electronic elements used.
The most useful article about applicability of different types of dimmers to different types of lamps you can read here
. If you understand Russian this is what you should start with.
Nearly in every article located on shop site you can read that transistor dimmer is better, more universal and it does not produce interferences. As far as I was making my own scheme and I wanted to make it good I've decided to use transistors. But I've managed to find only one
(actually, later I've found scheme of sinus dimmer
which uses IGBT too). But on every forum you would find variations with triacs. Looks like electornics engineers just do not feel a need for transistor dimmers.
Myth one. "Transistor dimmers are universal"
On symistor dimmer you can cut of only front side of a wave. Transistor dimmer can be build to cut any part of the wave. But when you buy specific one it would be L or C type. It would not be more universal than symistor one. Of course it is possible to build universal dimmer which can be switched between L and C modes, but it would cost more money and, anyway, you would not be able to use both load types simultaneously.
Another common statement sounds like: "Symistor dimmer can be used for incandescent lamps only and transistor one can handle halogen lamps with transformer." Actually symistor dimmers are good for electromagnetic transformers and transistor C dimmers are good for electronic transformers.
By the way, if you want to adjust motor speed with dimmer you would need to cut off front of the wave. But it must be interference resistant so usage of 3Q symistor instead of usual 4Q one is preferable. I'll cover this issue later.
Myth two. "Transistor dimmers do not produce interferences"
Let's find out what creates interferences. To control bulb brightness we have to switch it on very fast in the middle of the wave. For 50% brightness on the peak of it. This rapid current and voltage jump produces high frequency interferences. As far as these jumps occur 100 times a second they also induce low frequency interferences at 100 Hz and second and third harmonics. This low frequency interferences are in audible frequencies and mechanical oscillations in inductances and bulbs coils produces noise. So, these interferences originate from mechanics of how dimmer works and do not depend on elementary base used to build it.
With usual technique the only way to elude interferences is to skip whole wave periods. If you allow all periods you have 100% power, if you skip every second period you have 50%, one of four - 25%, three of four - 75%. This method is good for inertial loads such as heating coil in electriclak oven. But you can't dim light in such a way: your eye would notice bulb switching on and off.
Interferences can be filtered out. You can use throttle, RC chain, varistor. And, theoretically, dimmers with higher price should have better filters. But main problem solved by filters is not a protection of external devices: they protect dimmer itself from external interferences. Usual symmistor can spontaneously switch on because of fast current change. This may happen if you connect it to inductive load. You can even get a system with sustained switched on state. So the main problem solved by filters is prevention such situations.
There are special symmistors for controlling inductive loads. They are much less sensitive to interferences. You can read about them here
. Main idea is a sacrifice of one of operational modes (which is rarely used) for a higer interference resistance.
You can read a good article (in English) about sine wave dimmers
. These dimmers are based on IGBT (transistors) but used another power regulation method. Transistor switches with frequency about 10 kHZ making pulse width modulation of alternating current. Resulting peaks are smoothed by filter and you get real sinus with lower amplitude. So these dimmers do not make interferences in low frequencies. As a result you do not get audible noise. But if you look for them in internet you would find several attempts of making such dimmers at home and big and pricey theater solutions.
I think, that the reason is quite simple. If you want transistor which switches 10 000 times a second and does not overheat, then you need a fast transistor. Such elements cost more money. If you want to switch transistor as fast as it can than you need a driver (special electronic scheme) for it. It cost significant amount of money too. And this fast alternation makes a lot of interferences which usual power supplies of electronic devices do not filter out. So you need a good filter inside dimmer. Good filer is not only pricey but is also a big thing which is hard to put inside usual power switch.
So, as far as I understand, you would not find such dimmers at home sector.
What we have in conclusion?
You definitely need transistor dimmer if:
- You want to dim lamps powered with electronic transformer.
- You don't know which load type you would have and your dimmer can be configured to cut off any side of the wave.
- You need to dim lamp powered by DC. Notice, that transistor control scheme would be very different from one designed for AC.
You need to use 3Q symmistors if you want to control inductive load. 4Q may do a good job to if equipped with good filter. Bt it is easier and cheaper to use 3Q symmistor.
You can use any scheme you like for incandescent bulbs.
For my purposes I use BT137 symmistors. I had to understand whether I would be able to build a dimmer as soon as possible. So I've decided to use the most common scheme in the internet. If I would need to power electronic transformer I would just replace one of my modules.
There would be big separate post about my light control system with photos and sources.