Electronics > Beginners
Do any LEDs require ballasts?
bostonman:
--- Quote ---Some may argue the semantics - but, as a guiding principle - Yes.
Basically, with LEDs, you set them up to have their current controlled and the voltage will work itself out (Just as long as there is enough voltage to achieve the required threshhold).
In contrast, incandescent light bulbs are supplied with a specific voltage and the current works itself out.
--- End quote ---
Makes more sense as the response implied one needs to inject (as an example) exactly 100mA, else the LED will not light.
David Hess:
LEDs require ballasting to control their current because of their low resistance. Gas discharge tubes require ballasting because they have negative resistance. Magnetrons, like in a microwave oven, also require ballasting to limit current. Incandescent bulbs on the other hand have a large positive temperature coefficient of resistance so they are their own ballast and are sometimes even used to ballast other devices.
Resistance can be used as a ballasting element but this wastes power so typically inductance or capacitance is used in power applications.
Nusa:
--- Quote from: bitwelder on August 01, 2019, 02:22:08 pm ---
--- Quote from: Nusa on August 01, 2019, 10:21:03 am ---I suspect the confusion has to do with LED-based tubes for extant fluorescent fixtures. One version of the product is a plug and play replacement and is interchangeable with one in any fixture that takes that size tube. It also means the original ballast of the fixture remains in use. This is often the easiest route for many businesses to take, since their maintenance man or janitor can just replace old tubes as required.
--- End quote ---
Well, does this version of LED-based tubes allows or requires to use a fluorescent-type ballast?
And if it's possible to remove the old ballast, would be there any advantage in terms of LED operation in doing that? (a disadvantage could be the cost of the electrician called to do the change).
--- End quote ---
For instance, this one would require the ballast remain: https://www.amazon.com/AmazonBasics-LED-Tube-Light-Compatible/dp/B07BNJBX5T/
This one would require the ballast be bypassed: https://www.amazon.com/AmazonBasics-LED-Tube-Light-Compatible/dp/B07BNGX44F/
And apparently there are now hybrids, which can be used either way: https://www.amazon.com/Parmida-LED-Single-Ended-Double-Ended-Shatterproof/dp/B07FF91JHR/
Brumby:
--- Quote from: bostonman on August 01, 2019, 02:30:25 pm ---
--- Quote ---Some may argue the semantics - but, as a guiding principle - Yes.
Basically, with LEDs, you set them up to have their current controlled and the voltage will work itself out (Just as long as there is enough voltage to achieve the required threshhold).
In contrast, incandescent light bulbs are supplied with a specific voltage and the current works itself out.
--- End quote ---
Makes more sense as the response implied one needs to inject (as an example) exactly 100mA, else the LED will not light.
--- End quote ---
The issue with LEDs and their current is not so much for currents that are at or below their nominal current, but when you start exceeding this. Your typical LED nominally rated for 20mA will still produce useful light output at 15mA - just not as bright. You can also see one light up with a current of 1mA - or even less - but you will need to look more closely to see it.
Where LEDs have a problem is when the current exceeds the rating. Provide power with a voltage higher than Vf and you will get a brighter LED - but at the cost of a shorter life. The real danger with not having current control is that as you nudge the voltage higher and higher, your LED will start conducting current at a dramatic rate.
To find out how any given LED will respond, you just need to check out the appropriate chart on its datasheet - but here is one to illustrate the general features of such a chart. You will see that different colours have similar responses, but at different voltages - and that the nominal voltage for any given LED will be for a stated current.
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