In article , David Combs wrote:
In article ,
John Grabowski wrote:

hotter than they are suppose to. The new electronic ballasts don't get as
hot.

What *are* these electronic ballasts? How do they work -- as compared
to the other ones (get hot)?

The more-old-fashioned ballasts are either inductors or "high leakage
reactance autotransformers", and the latter often have lamp-series
capacitors. Inductance (or a proper combination of inductance and
capacitance) limits/controls the amount of current flowing through the
lamps.

The more-modern "electronic ballasts", at least the ones for non-compact
fluorescents, appear to me to work by:

1. Rectifying AC to DC
2. Using an "inverter circuit" to convert the DC to a much higher
frequency AC (hundreds of times higher)
3. Using inductors or capacitors or both to limit/control current.

At the much higher frequency, inductors and transformers work well from
ferrite instead of "transformer steel" (to achieve lower core losses), the
cores are smaller (helps greatly against core losses), and windings get to
use much shorter lengths of wire (greatly reduces winding resistance
losses).

Furthermore, fluorescent lamps operated at power line frequency AC often
have a minor loss mechanism known as "oscillatory anode fall", which is
eliminated by use of AC of a frequency higher than the anode fall
oscillation frequency.

One more thing - narrower 2 and 4 foot fluorescent lamps (typically
powered by electronic ballasts) use premium phosphors whose cost gets more
prohibitive in the wider older sizes.

- Don Klipstein )