G8MNY > TECH 13.06.25 07:15z 123 Lines 5900 Bytes #176 (0) @ WW
BID : 34627_GB7CIP
Subj: TRIAC Light Dimmer
Path: ED1ZAC<ED1ZAC<GB7CIP
Sent: 250613/0704Z @:GB7CIP.#32.GBR.EURO #:34627 [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 1M
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 half 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
half way along the half 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 half cycle. The Traic is then triggered & provides the very low voltage
mains at the end of the half 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
+/- 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 330R 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 ± 10K ± 50K
ÄÁÄ 1kV ³ ± ±<Ä¿
/// ³ .1uF ± ± ³
³ ³³250VAC ³ ³ ³
ÀÄÄÄÄÄ´ÃÄÄÄÄÄÄÄÄÄÁÄı±±±ÄÄÁÄÄÙ
³³ 1K
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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