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G8MNY > TECH 17.04.04 08:12l 69 Lines 3248 Bytes #999 (0) @ WW
BID : 53167_GB7CIP
Read: GUEST OE7FMI
Subj: TRAIC Light Dimmer
Path: DB0FHN<DB0FOR<DB0SIF<DB0IDN<DB0AIS<DB0ZDF<DB0LJ<LX0HST<HA3PG<7M3TJZ<
ON4HU<WU3V<GB7CIP
Sent: 040417/0007Z @:GB7CIP.#32.GBR.EU #:53167 [Caterham] $:53167_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (New Graphics Dec 03)
Here is a simple circuit used in most dimmers.
Live ÄÄLAMPÄÄo/oÄÄÂÄÄÄÄ()))ÄÄÄÄÄÂÄÄÄÄÄ1KÄÄÄÄÄ¿ - - - - ¿
110-250V FUSE ³ CHOKE A''³ 1W POT 1Mê
50-60Hz ³ __³__ 100K _³_ LOW BRILLIANCE
³ TRIAC \/ /\ Diac ³(2W) \ / DC OPTION
Filter === ÄÄÂÄÄ ³>³ ³ ÄÂÄ 400v PIV
caps 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.
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
³ ³ ³ _³ ³_ ___³ ³___ ___³\______ __ _³\_______
³ ³ ³ ³ ³ ³ ³/
³ ³ ³ ³ ³ ³
\__/ \__/ ³_/
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 TRAIC 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!
Why don't U send an interesting bul?
/QSL
73 De John, G8MNY @ GB7CIP
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