From: Harold Hallikainen <harold@mai.hallikainen.org>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Wed, 25 Nov 2020 09:17:28 -0800
Subject: Re: [OT]  Hyperikon Retrofit LED Tubes Without Ballast
Thread-Topic: [OT]  Hyperikon Retrofit LED Tubes Without Ballast
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This discussion reminds me of just how interesting fluorescent lamps are.
Wikipedia has a nice article at
https://en.wikipedia.org/wiki/Fluorescent_lamp .

Many years ago, I did some work on fluorescent lamps for television
lighting. I always thought the ballast was interesting. An oscillator with
an H-bridge drove the lamp. The H-bridge drove the lamp through an
inductor. The H-bridge with series inductor was connected to one filament
pin at each end of the lamp. A capacitor connected the other filament pin
at each end of the lamp. Before the lamp fired, the LC was resonant
causing a high current through the filaments, lighting them. The resonance
also created a high voltage across the capacitor and across the tube. The
filament heating and high voltage across the tube would ionize the gas,
shorting out the capacitor. The inductor then became a current limiter.

I always thought that was VERY clever!

Harold



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