Homebrew PCBs

The CFL act just similar to a flashlamp. They have negative resistance 
curves - initial high impedance and then low impedance once the arc is 
drawn. Takes me back a couple of decades to my flashlamp days of 20kW+.

Derek Koonce
DDK Interactive Consulting Services



On 11/4/2011 8:58 AM, designer_craig wrote:
>
> I have found the small 2 pin U lamps are actually 4 pin internally 
> with filaments. Inside the base one pin from each end of the lamp are 
> connected together through a capacitor.
>
> I suspect one could remove the cap and use a normal 4 wire ba1last, a 
> series inductor with click starter or even a push button switch 
> starter with series inductor. Got to be a billion ways to make these 
> things work.
>
> Here is how the two pin (with cap bulbs work) CFL bulbs work. To start 
> the bulb the electronic balast puts out a frequency that resonates 
> with the series cap and its output inductor. This allows current to 
> flow through the bulbs filaments and heats the mercury vapor. Also 
> because of the resonance there is a fairly high voltage across the cap 
> ( big phase shift here). The high voltage eventually causes an arc to 
> form in the tube drastically lowering the tube's internal resistance 
> and the voltage across it from well over 100V to to less that 60V 
> depending on temp. Once the arc if formed the tube's resistance is 
> very low compared to the caps reactance and the cap is effectively out 
> of the circuit. Then it's just the electronic chopper driving the tube 
> through the output inductor to limit the current. The CFL's circuit is 
> very crude but effective.
>
> Ever wonder why you don't get 25 years out of the CFL's -- they are 
> built so cheaply without any line transient protection. One 
> overvoltage spike and it's toast.
>
> You can actually buy a low cost CFL, hack the board out of he CFL and 
> use it on your UV light. Just remember chopped 168V non isolated power 
> will knock you off your chair.
>
> Craig
>
>