gregz wrote in news:1216010132358050972.266977zekor-
:

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


I took apart a cheapo dollar store 60W CFL(spiral type),and the ballast was
a 2 transistor circuit with a tiny ferrite core transformer and a couple of
electrolytic caps configured as a voltage doubler,that rectified and
doubled the input line voltage. this was all in a space the size of a new
dollar coin.

The input V is rectified and doubled to around 300-320 VDC,then the
transistors switch the DCV through the transformer to generate the higher
AC voltage to power the FL tube. The tube filaments are in series across
the transformer output and are energized at cold start by the high
impedance across the tube until the arc discharge begins.the arc
effectively shorts out the filaments,so they don't burn up during normal
operation.

I doubt that throwaway CFLs will have any surge protection.

I suspect that the wear items for an electronic ballast will be the
electrolytic caps,as they are in other power supplies and electronic
circuits.

--
Jim Yanik
jyanik
at
localnet
dot com