Re: Light output of dimmed lamps

In article <HrFrf.2484$nu6.2208@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>, Steve
Kraus wrote:
>> And a phase shift cap and a diac in series with the pot.
>
>But a pot and triac alone will give you a working dimmer.

Pot and triac alone can sometimes make an unreliable one variable from
close to full, down to half of each half cycle going through, and needs a
higher wattage pot. That would work by varying what point in the waveform
the pot lets through enough current to trigger the triac.
They don't do it that way. For one thing, tolerances in trigger current
in the triacs would be a big issue.

The usual dimmer also has a capacitor and a diac. The pot (used as a
rheostat) adjusts the amount of time it takes the capacitor to charge up
enough to cause the diac to become conductive. Then the charge in the
capacitor discharges through the diac and the gate of the triac.
This arrangement does limit the range of the waveform at which the triac
starts conducting to the range where the instantaneous voltage exceeds the
breakover voltage of the diac. Most dimmers without a "positive on" do
not let lamps reach full brightness.

- Don Klipstein (don@xxxxxxxxx)
.

Relevant Pages

  • Re: Light output of dimmed lamps
    ... >> And a phase shift cap and a diac in series with the pot. ... > But a pot and triac alone will give you a working dimmer. ... across the triac is a function of the gate voltage, ...
    (alt.home.repair)
  • Re: Lamp Dimmer
    ... They did have a TNE5646 "Triac with Internal Trrigger ... Diac", which I purchased. ... circuit board, squirted in some tuner cleaner, and worked the shaft. ... Now the pot works good mechanically and electrically but the switch is ...
    (sci.electronics.repair)
  • Re: Light output of dimmed lamps
    ... > And a phase shift cap and a diac in series with the pot. ... But a pot and triac alone will give you a working dimmer. ...
    (alt.home.repair)
  • Re: Ansteuereinheit =?UTF-8?B?ZsO8ciBNT1NGRVRz?=
    ... So stell ich mir das vor: Ein Diac ist ein offener Schalter. ... Triac schaltet nicht. ... Triac hängt an dem Spannungsteiler 180 Ohm zu Last. ... seien 0V), dann fließt erstmal aller Strom durchs Gate, Vorwiderstand ...
    (de.sci.electronics)
  • Re: Konventionelle Dimmerschaltung
    ... Die Spannung am Widerstand eilt der Spannung am Triac vorraus. ... dort (und somit auch am Diac) gerade 33V erreicht, ...
    (de.sci.electronics)
Loading