I came across a circuit to power a small 11watt CFL, but instead of the primary / secondary winding, this one had a 3 winding for feedback?

What's the purpose of the feedback coil? I've noticed that some transformers have 6 sets of pins not the usual 4 sets (ac in > ac out) ? what's the purpose of a feedback coil?

For example, if i used a 555 IC i could feed directly into the in and out comes the required voltage (obviously with a few components in-between ) .. I'd not need a feedback coil? so what's the purpose of one?

 

What's the purpose of a drawing?

Send one.

 

What's the purpose of a drawing? do you lack the imagination to imagine a transformer (of any size) with 6 pins? a drawing is not going to help you answer the question, what is the purpose of a feedback coil....

 

Depends on what it's connected to.

 

You may be describing a very common oscillator circuit using the "third" winding as part of the oscillator. One use is for model ignitions. In that case, the secondary will have 200 to 400 turns, the primary about 30 turns, and the third about 15 to 20 turns. Here is one of very many examples used for a model ignition system. Similar circuits can also be used for CCFL.

John

 

I still don't know if the CFL power device has an oscillator or if it's a "brute force" step-up transformer with a filament winding, but there's 2 possible answers right there. The third winding might run an oscillator or it might be a filament heater. Other possibilities are limited only by my imagination.

 

One purpose for a feedback coil would be to determine when the primary coil was saturated; thus time to turn off the current.

 

TSK TSK....feedback.
the name says it all, the feed back coil feeds a portion of what is applied to the primary coil back to the driver. By this way the driver can check for core saturation

 

Glad we got that settled. The purpose of the feedback winding is to give feedback to the driver.

 

Just don't let Rifaa drive the bus, unless it's watertight and is equipped with a snorkel.

And sandwiches. Lots of sandwiches.

 

You'll need high pressure suites to go with it

 

We're strictly low pressure here.