Dimmer - Bulb replacement, light comes on?

With dimmer off

When a globe Blows and you replace it the light goes on then off for 0.5 Seconds.

What causes this....

 

Charlie

Err, a little more explanation please.

Is the channel always in the On state during this sequence? What types of loads are being used? Did the load blow at turn-on or after running for some time? Does it cycle on and off repetitively or does it only turn off for 0.5 seconds once?

 

Phase control dimmers work by chopping the mains signal. A Triac or SCR is the device typically used to chop the waveform. At dim settings the load sees a small portion of the mains signal. At brighter settings the load sees more of the mains signal and at full brightness the load sees practically the whole mains signal.

Phase control dimming works because the total power that the load draws changes as the mains signal is chopped. The current is limited but it happens as a consequence of the mains being chopped, rather than the current being specifically limited. A true current-limiting dimmer would be very expensive to manufacture and, for the most part, give no benefit over phase control dimers.

Now as for the current in the load, well, that depends upon the type of load. If it is a primarily resistive load (incandescent typical), then the voltage and load will be "in phase" and the two will roughly track each other. If, however, we connect a perfect inductor then the current will lag the voltage by 90 degrees. Likewise if we connected a perfect capacitor then the current would lead the voltage by 90 degrees.

This is related to the dimming architecture but not a direct result of it as such. All dimming products sold in Australia are required to comply to various EMC standards and to do this certain filtering componnets must be fitted. These filtering components allow a small amount of power to still flow through the load in the off state as they effectively by-pass the primary switching elements.

 

Bulb Replacement

Could this have something to do with minimum channel loads on dimmers. For memory, dimmers require a minimum load (20w for memory) to function????
Perhaps, due the faulty lamp, the channel can not go off due to no minimum loading when a lamp blows. When the lamp is replaced, added load back onto the dimmer, could this cause the channel to then actually turn off after a slight delay?????

 

My Guess is ;-)
Its due to the snubber circuit (rc network) discharging into the globe when initially connected.....

Frank

 

I'm agree with you Frank.

If anybody is interested in some more details, have a look at this.

http://www.epanorama.net/documents/lights/lightdimmer.html