Originally Posted by hsab

we can use it at home when light cut off

Why did your lights get cut off? Did you forget to pay your electricity bill?

Flourescent are more efficient than LEDs, well for producing white light anyway.

The problem with this circuit it it drives the tube of pulsed DC not AC so it won't be as birght and it won't last as long. You need a push-pull driver and centre tapped transformer primary to get an AC output and drive the lamp properly.

http://www.electro-tech-online.com/156617-post7.html

That isn't a very good way of doing this, please refer to my post linked above.

Originally Posted by Hero999

Flourescent are more efficient than LEDs, well for producing white light anyway.

The problem with this circuit it it drives the tube of pulsed DC not AC so it won't be as birght and it won't last as long. You need a push-pull driver and centre tapped transformer primary to get an AC output and drive the lamp properly.

The output of the transformer shown is still AC! However that type of drive is indeed inefficient and makes poor use of the magnetic core. The output may be a bit "spikey" too.

Rolf, what Hero999 says is accurate- good flourescents are more efficient than LEDs.

Starting and driving a flourescent is a bit tricky, and requirements vary from tube to tube. Of particular interest is that the impedance of the tube changes as it ages or just warms up. A fixed voltage may either not be enough to drive the tube with enough current OR it will provide the tube with too much current. I'm not big on home-grown solutions myself because it's such a complicated task to do right.

Originally Posted by Oznog

The output of the transformer shown is still AC!

I believe we've seen this discussion on this forum before. The transformer's primary is driven by one transistor connected to a positive supply. When the transistor shuts off the back-emf generate by the field around the primary collapsing induces a large negitive pulse in the secondary, this repeates continiously. Hence it is generating pulsed DC not AC. The pulses travel in one direction only, from the cathode to the anode causing the catode to be brighter and excess electrode sputter around it, this isn't good. One solution to this problem is to simply add a capacitor in series with the tube, this will effectively block the DC level (remember pulsed DC is simply an AC voltage plus half it's peak value DC offset).

Originally Posted by Oznog

However that type of drive is indeed inefficient and makes poor use of the magnetic core.

True, because the pulses are only one polarity the same is true for the field, in effect only half the magnetising potential of the core is being used.

Originally Posted by Oznog

The output may be a bit "spikey" too.

That's an understatement, there's a heave peek at the start of each pulse followed by ringing (which may be damped when the tube ignites).

Originally Posted by Oznog

Rolf, what Hero999 says is accurate- good flourescents are more efficient than LEDs.

To date this is correct, but while fluorescent tube technology is mature LEDs are continuing to improve, it's only a matter of time before they beat fluorescents.

Originally Posted by Oznog

Starting and driving a flourescent is a bit tricky, and requirements vary from tube to tube. Of particular interest is that the impedance of the tube changes as it ages or just warms up.

It starts off open circuit before ignition and drops one struck, then continiues to drop as the current increases until either there's no more gas to ionise or the wiring resistance or fuse limits the current.

Originally Posted by Oznog

A fixed voltage may either not be enough to drive the tube with enough current OR it will provide the tube with too much current.

A constant current source is idea but this is normally approximated by a large inductor, at mains frequencies, or with a high frequency inverter a capacitor can be used (which will also solve the pulsed DC problem). Often the transformer is specially designed to have a very high leakage inductance to limit the current, this is true bot for some mains ballasts and inverters.