RE: ELECTRONIC BALLAST?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Trimmell" <humanb-at-chaoticuniverse-dot-com> 

With my BK frequency counter I get 44 KHz or 98 KHz depending on
manufacturer tested. I have not had any interference problems, even with
a low Fre shortwave down to 150 KHz. Quality has markedly improved with
these since they showed up on the consumer market, but the 5 year ones
usually fail 2-4 years, so far in my experience.

Regards,

David Trimmell

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Monday, August 09, 2004 3:28 PM
To: tesla-at-pupman-dot-com
Subject: Re: ELECTRONIC BALLAST?

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz>

On 8 Aug 2004, at 18:53, Tesla list wrote:

  > Original poster: "Ed Phillips" <evp-at-pacbell-dot-net>
  >
  > Anyone have a clue as to the circuit of the ballast/power supplies
for
  > screw-in  fluorescent lamps?  Just cut a dead one apart and found
more
  > stuff than I expected.  Six diodes, 2 HV transistors, one diac, one
  > PTC resistor, two inductors (one closed ferrite core with fairly
heavy
  > wire), two 22 ufd, 200V electrolytics and miscellaneous other
  > resistors and capacitors.  A lot more stuff than I expected and that
  > probably explains the RF interference they generate.
  >
  > Ed

Hi Ed,
         The circuitry is basically a flyback inverter running from
rectified and smoothed mains. There is a crude RF filter in the form
of a choke at the input. The real surprise for me is that these
things simply use a cap input filter running from a bridge rectifier.
I would have expected the inverter to be a simple active PFC type
with little or no input smoothing capacitance. Not hard to do except
that it would require a multiplying controller which adds to the
cost. The interference is bad for sensitive radio eqpt but our house
is fully equipped with these things and it's not so bad that it
interferes with the TV which is using and indoor rabbit's ears
antenna.

Malcolm