OT: Just a thought.

Balast? On LED's?

LEDs are current devices. Something has to absorb the excess voltage when you control the current supply to it.

Basic woodworking101.

LED's are diodes. To power it from a 120vac source, one needs a small

It take a few more components than that. LEDs can't stand up to much PIV. Your lack of electronics knowledge is showing but to use your oversimplified analysis shows what a ballast could be composed of.

Calculate this 120 Vac across a 1K resistor. First of all your half-wave rectifier will net you about 180 Vdc if smoothed by a cap. That's a ballast loss of about 180 v squared / 1000 Ohms or 32.4 Watts of loss to run a half Watt LED in YOUR ballast circuit. IT would not be done this way but I had fun....LOL It would be done with high frequency inverter / P.S. and more complex circuits.

Just wait until tonight when GW gets out of school and will straighten you out. He knows everything! LOL

---------------- On Jul 20, 10:58 am, "m II" wrote: LEDs are current devices. Something has to absorb the excess voltage when you control the current supply to it.

Basic woodworking 101.

It was oversimplified for a reason. But you seem to like the word 'ballast' so by all means use it (wrongly).

And you should make that correspondence course from a matchbook cover give you your money back.

Ok you are the expert, you have read something some where gotten it all confused and believe you know it all. I on the other hand actually have BACK- LIT florescent LCD and LED back-lit LCD screens and the fact that the LED set produce little to no heat compared to the floresent LCD must be my imagination. I'll go with my imagination.

In a store there could be other contributing factors to make the LED set seem warm. I never put any thought to it myself as I knew that florescent LCD screens were quite cool compared to the old tube screens but still put out a small amount of heat. One day I was checking the LED LCD screen at home and the top of the set was room temperature after being on all day.

types.http://hometheater.about.com/od/televisions/qt/ledlcdtvfacts.htm>>> I put my hand on a few sets while we were looking at TVs and the LCD

If you are shopping be careful to not rely on that to differentiate. Many retailers will put a protective coating on the screens on both LCD and plasma screens as an add on to the sale. Those protective films come in glossy and matte finishes. Not saying that is what you saw but it is often hard to tell a plasma from an LCD. I have found that the sure fire way to tell is lift the corner, plasma sets are still damn heavy sets by comparison.

Toss in disc#1 of BBC's Planets BluRay and I will tell you in a few seconds which is which. It is becoming more difficult, mind you as the LED/LCD are at 1080p and fast refresh rates (Where are we at now/

Also... a dead give-away is when the sales guys keep saying things like: "Those new LED/LCD are getting as good as plasma......."

Nothing, absolutely nothing, in the set runs on 120V. An efficient switching regulator reduces your 120V, or 240V if you live elsewhere in the world, down to more useful voltages. Modern LED drivers also use switch mode technology to increase efficiency and reduce energy loss through heat to a minimum.

Well, I know that, you know that.....

Your capacitor (or resistor, switching current source, whatever) is the ballast. Something has to limit the current. Yes, it's called a "ballast". ;-)

It's not wrong.

The switching regulator is limiting the current. It's really an "electronic ballast".

load=3Dballast. Check.

types.http://hometheater.about.com/od/televisions/qt/ledlcdtvfacts.htm>>>> I put my hand on a few sets while we were looking at TVs and the LCD

I didn't care, since the plasmas are all heaters. I won't buy one.

-- Always bear in mind that your own resolution to succeed is more important than any one thing. -- Abraham Lincoln

PDFTFT

-- Always bear in mind that your own resolution to succeed is more important than any one thing. -- Abraham Lincoln

No, current_limiting_device == ballast. It does the same thing as an electronic ballast in a fluorescent fixture.