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Jim Yanik Jim Yanik is offline
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Default What's inside of these modern electronic ballasts

Peter wrote in :

On 5/7/2012 10:27 AM, Jim Yanik wrote:
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.

Nothing like good old planned obsolescence. How much would it really
cost the manufacturers to substitute electrolytic caps with somewhat
higher power ratings? I'd gladly pay an additional $0.20 - $0.50 per
CFL or fixture for substantially longer mean time before failure.


the caps in there are 105degF 250V caps,seem to be rated fine.
electrolytics DO have a finite lifetime,usually several thousand hours of
operation. But the CFLs often are in "hot" environments that shorten their
lifetime. That's why many are not rated for "base up" operation;the ballast
receives the heat from the fixture.

switcher power supplies usually put a fast rise waveform across the
caps,that have high harmonics and generates a lot of internal heat.
electrolytics lasted a lot longer at 60Hz frequencies and sine-wave
operation.

--
Jim Yanik
jyanik
at
localnet
dot com