On Mon, 7 May 2012 02:37:31 +0000 (UTC), gregz
wrote:

wrote:
What's inside of these modern electronic ballasts for florescent shop
lights and other straight tube fixtures? I know these ballasts are
being sold more and more to replace the old iron core magnetic types,
but what's going on inside of them? Obviously there are semiconductors
and other electronic components. I would suspect that a capacitor
discharges to start the bulbs.

I tried to google a schematic, found several showing how to wire them
(same as the old style ballasts), but none show the innards or a
schematic that explains how they work.

I also wonder how durable and reliable they are compared to the old
ones? Electronics are often more likely to burn out from power line
surges caused by lightning and load surges. Since surges occur in all
electrical systems, are the electronic types as durable as the old coil
wrapped around iron ("transformer") types.

Thanks

You got bridge to make dc, mosfets to switch at high frequency, inductor
and caps.
More efficient but probably less reliable, but ballasts break too.

Greg


Several years back I noticed that the tubes in my newer 48" fixtures
were burning out fairly fast, like within a year or two. Googling for
info at the time (at least 5 years ago now) I found that the life
expectancy for the tubes when used in electronic ballasted fixtures
was less then half the expected life when used in magnetic ballasted
fixtures. I replaced those "new" fixtures with mag ballasted new ones
and started getting my usual 3 to 5 years of life again. I also
noticed that in our commercial building all the ballast for the
fixtures continues to be mag ballast, not the electronic crap.