Old 12V FL driver with hot transistor

[Simen]

I got an old 12V, 13W FL driver with a 2SD234 transistor, rated 3A, 60V, 25W, which runs rather hot. Originally, the transistor was connected to the aluminium frame of the lamp, thus getting enough cooling that way, but i need to run it without a large coolingfin.

As i understand it, a fet transistor handles on/off switching much better than an ordinary transistor and thus doesn't get that hot.

Could i swap the transistor directly with a fet with same or better spec? (there is currently a 470ohm resistor in series with the base; would that one need to be lowered with a fet in place?)

Got some pictures here:

http://www.mwlmf.net/gallery/12V-cfl

I've moved all the components from the original circuit board to a new one, because the old one was broken in two and both burned and corroded. (it has been in a sailboat since '74 ) Also, i'm currently using a 11W cfl tube.

[Flux]

No you are dealing with low and awkward technology and you will be into a serious redesign if you start messing.

Those single transistor drivers are inefficient but simple. There are infinitely better options but it is far from simple. With leds coming down in price I see the days of these cheap single ended fluro drivers being numbered.

Flux

[margusten]

Hi,

I made simple 12V driver like Yours.

I have exactly same problem - transistor wery hot.

I thought the problem is parasite self generation, added some extra capasitors but nothing.

This idea is good to use FET transistor.

I found something:

http://www.fieldlines.com/story/2006/9/1/05223/63405

Can I just use 555 generator and FET?

I have a lot of used (not working) compact flurecent lamps (220V).

I found their problem broken electronics, four tubes of five working.

BR,

Margus

[David HK]

Go to this web site and you will find out a great deal more on CFL circuits.

http://www.pavouk.org/hw/lamp/en_index.html

David HK

[Simen]

I also have read that post, and the thread by Commanda it refers to:

http://www.fieldlines.com/story/2005/6/3/62548/82431

Commanda uses a very simple circuit with a mosfet, so i wonder if i should experiment a bit here... (probably test some different capacitors to get the frequency right etc...)

Commandas circuit uses 2 wires to the fl; mine has 4, as the cfl i'm testing with.