Sean Breheny wrote:

> <SNIP>
>
> Speaking of triac based light dimmers, when designing one of these, does
> one need to take into accout the heating and cooling of the lightbulbs?
> When the triac switches off, the lightbulb will cool somewhat,and its
> conductivity will be higher when it gets switched on, which I would
> immagine would cause LOTS of current spikes at low duty cycles. Is this
> ONLY an EMI concern, or might it decrease the lifetime of the bulb, as well?
>

In the work that I have done with lamps and dimmers, I found that when the bulb
filament is relatively 'hot' between on cycles it prevents the bulb from
experiencing inrush.  If I recall my work some years back on lamps, there is a
saw tooth of current generated, and the longer the period (and thus off time)
the higher the saw tooth of current max goes.  BTW, the one thing I looked into
was whether or not all of the pulsing DC caused a loss of life for the light
bulb.  I really poked around some of the manufacturers, and none that I talked
to had ever done any data on PWM effects on hours of life.  Yet it is a common
practice. ( or is that practise, spelling fanatics?)

Chris Eddy, PE
Pioneer Microsystems, Inc.

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