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G8MNY  > TECH     17.07.19 09:36z 124 Lines 5886 Bytes #999 (0) @ WW
BID : 12675_GB7CIP
Read: GUEST
Subj: TRIAC Light Dimmer
Path: HB9ON<IW2OHX<IR2UBX<F1OYP<ON0AR<VE2PKT<ZL2BAU<N9PMO<GB7YEW<GB7CIP
Sent: 190717/0933Z @:GB7CIP.#32.GBR.EURO #:12675 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                                         (Updated Aug 10)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

Here is a simple circuit used in most dimmers.
                        ====
Live  ÄÄLAMPÄÄo/oÄÄÂÄÄÄÄ()))ÄÄÄÄÄÂÄÄÄÄÄ1kÄÄÄÄÄ¿ - - - - ¿
110-250V     FUSE  ³   CHOKE  A''³     1W   VARIABLE   1Mê
50-60Hz            ³           __³__         100k      _³_ LOW BRILLIANCE
                   ³    TRIAC  \/ /\   Diac   ³(2W)    \ / DC OPTION
           Filter ===          ÄÄÂÄÄ    ³>³   ³        ÄÂÄ 400V PIV
            cap    ³ 47n       A'³ \ÄÄÄÄ´ ÃÄÄÄ´         ³
         "X" rated ³ 250V        ³ Gate ³<³   ³ - - - - Ù
                   ³ AC          ³           ===
                   ³             ³       0.1u ³
Neutral ÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÙ

The circuit is shown here on the Neutral but in practice may be in the LIVE
side. It is not really suited to Transformer loads as there is a risk of DC
output, but some makers do use it into transformers!

FILTERING
Filtering must be provided to reduce the high frequency content of Anode A''
from getting out of the dimmer. The Choke is often 20 turns on a small ferrite
rod or ring.

TRIGGERING
The DIAC is a 20-30V (20V on 110V) device, when the 0.1uF cap charges up over
its' strike voltage, the 0.1uF charge is dumped into the TRAIC gate. I have
seen 2 identical low voltage transistors used as instead of a diac, when they
avalanche they produce a similar action, provided the current is not excessive.

                        +30V ³     Breakdown
 Bases not connected         ³_.-'³
   __³___   __³__            ÃÄÄÄÄÁÄÄÄÄÄÄÄÂÄ
____/ \e____e/ \____         ³        '-._³
                        -30V ³

AT FULL BRILLIANCE
When the pot is set to minimum, the 0.1uF cap charges up through the 1k almost
instantly. The CR provides some false spike mis-trigger protection. So the
TRIAC is triggered when the Live is about 30V, & stays on, lighting the lamp
until the mains is gone to Zero volts at the end of the « cycle.
  __               __               _
 /  \  MAINS      /  \   FULL      ³ \   HALF         MIN             DC
³    ³  IN       ³    ³  POWER     ³  ³  POWER        POWER           MOD
Ý     Ý      Þ  _³     Ý_        __³   Ý___      __³\_____  __   _³\_________
      Þ      Ý          ³     Ý           ³   Ý           ³/
       ³    ³           ³    ³            ³  ³
        \__/             \__/             ³_/
                                         Max QRM!

AT HALF POWER
When the pot is about half way around, the 0.1uF capacitor reaches 30V around
« way along the « cycle when triggering occurs. This still produces the full
peak voltage, & generally causes the most QRM, but only half the energy is
delivered to the lamp.

AT MAX DIMMING
When the pot is at maximum the 0.1uF cap only just charges up 30V near the end
of the « cycle. The Traic is then triggered & provides the very low voltage
mains at the end of the « cycle to the lamp, until Zero volts releases the
traic ready for re-triggering.

DC LOW DIMMING IMPROVEMENT
Due to the uncertainty of triggering the TRIAC when the mains is low etc, as
the 0.1uF may not reach the 30V required, a modification to the circuit is
sometimes incorporated. This applies a small amount of DC to the 0.1uF cap as
the POT resistance increases. This actually puts out unequal portions of the
ñ mains phases causing the non triggering effect to be reduced. But the DC or
half frequency (50Hz not 100Hz) powering can cause visible flicker in small
power lamps! If used on Transformer excited lamps, it will burn out the
transformers!
-------------------------------------------------------------------------------
from Lod LW1DSE...

It is impotant to add to your intresting bul, that this devices generates lots
of harmonics, that can be irradisted from the load and line wires, acting as
antennas (aerials), and causing lots of QRM's to some sensitive devices.
(TV's, AMradios, ham's, etc) So, I made one of them incorporating a double LC
filter, one in common mode, an other in differential mode to prevent the
harmonics to exit via the wires. This is my circuit, actually in use:

                                         ³³
                        ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´ÃÄÄÄÄÄÄÄ¿
                   .47æF³                ³³.22æF  ³
                  250VAC³ ³³  330ê 1W      250VAC ³
                        ÃÄ´ÃÄÄı±±±ÄÄ¿            ³
        2 * 39mH  .01æF ³ ³³         ³    100æH   ³
                 ø 1KV  ³      ³<³   ³            ³
L OÄÄo\oÄÂÄÄÄÛÛÛÛÄÄÄÂÄÄÄoÄÄÄÄÄÄ´ ÃÄÄÄÁÄÄÄÄÛÛÛÛÄÄÄÄoÄÄÄÄÄO
         ³  ======  ³   ³      ³>³\      ======   ³
         ³      // ÄÁÄ  ³ TRIAC    ³              ³
220VAC  ÄÁÄ    //  ÄÂÄ  ³ BTA24/800³              ³
        ÄÂÄ   //   ÄÁÄ  ³          ³ ³<³  DB3     ³    LAMP
         ³   //    ///  ³          ÀÄ´ ÃÄ¿DIAC    ³
         ³  //          ³            ³>³ ³        ³
    2Amp ³  ======      ³                ³        ³
N OÄÄo~oÄÁÄÄÄÛÛÛÛÄÄÄÂÄÄÄ(ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ(ÄÄÄÄÄÄÄÄ(ÄÄÄÄÄO
                 ø  ³   ³                ³        ³
     1æF 250V      ÄÁÄ  ³     ³³         ³        ³
      AC X2        ÄÂÄ  ÃÄÄÄÄÄ´ÃÄÄÄÄÄÄÄÄÄ´        ³
                   ÄÁÄ  ³     ³³.47uF    ³        ³
T OÄÄ¿           .01uF  ³       250VAC   ± 10Kê   ± 50Kê
    ÄÁÄ           1KV   ³                ±        ±<Ä¿
    ///                 ³       .1uF     ±        ±  ³
                        ³     ³³250VAC   ³        ³  ³
                        ÀÄÄÄÄÄ´ÃÄÄÄÄÄÄÄÄÄÁÄı±±±ÄÄÁÄÄÙ
                              ³³            1Kê

Good luck, and best regars from Barrio Garay, Buenos Aires Argentina!!!

-------------------------------------------------------------------------------

See my buls on "Transistors, SCRs & TRIACs" & "SCR Drill Speed Controller",


Why don't U send an interesting bul? 

73 De John, G8MNY @ GB7CIP



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