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Old 10-08-2009, 01:15 AM   #1
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Default Do LED's need a ballast?

Hello,

'Thought' I knew the answer to this question, but now I'm not 100% sure.

I have heard that LED's, if rated at correct voltage, did not need a ballast.

Is this true?

Much appreciated!!!

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Old 10-08-2009, 01:29 AM   #2
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Not that I know. They may need a resisitor, though.

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Old 10-08-2009, 01:57 AM   #3
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most LED's need 1.5 volts DC. So: they need a rectifier, and a resistor.

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Old 10-10-2009, 12:32 AM   #4
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Alot of them need led drivers(ballasts)
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Old 10-10-2009, 02:17 AM   #5
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Quote:
Originally Posted by Elec-Tech View Post
Alot of them need led drivers(ballasts)
Well, what are we specifically talking about? A LED lamp, or a single LED? He said LED, so all it needs is correct Direct Current.

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Old 10-10-2009, 02:49 AM   #6
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Quote:
Originally Posted by TOOL_5150 View Post
Well, what are we specifically talking about? A LED lamp, or a single LED? He said LED, so all it needs is correct Direct Current.

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This is true...need a little more info.
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Old 10-10-2009, 09:24 AM   #7
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Quote:
Originally Posted by TOOL_5150 View Post
Well, what are we specifically talking about? A LED lamp, or a single LED? He said LED, so all it needs is correct Direct Current.

~Matt
I see nothing about an LED lamp or bulb in the OP.



I just see a question about LEDs.
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Old 10-10-2009, 12:00 PM   #8
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I seem to recall an LED that was red with forward polarity and green with reverse polarity when you supplied it with ac it was yellow.

Or was that neon?

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Old 10-10-2009, 12:06 PM   #9
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An LED by definition is a diode so it doesn't need a rectifier to operate.

That being said, connecting a pure LED to an AC source will cause it to "flicker" as it will only be lit half of the time.

If you use a rectifier in a power supply for an LED, that is simply part of providing a DC source to make the LED stay lit 100% of the time.

LED "drivers" as they are called are simply regulated power supplies, which may contain one or more of the following: Transformers, rectifiers, resistors, capacitors, etc. Calling that a "ballast" would be a loose translation, IMO.
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Old 10-10-2009, 03:08 PM   #10
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I beleive the driver circuit would look something like this (full wave bridge rectifier) with the possable addition of a small dielectric filter
http://www.faqs.org/docs/electric/Semi/03263.png


added
BALLAST CIRCUITS FOR DISCHARGE LAMPS
http://www.freepatentsonline.com/3787751.pdf

certainly very similar, the only difference i see is the ballast contains a capacitor (probably as a filter) If the driver contains one as well then its pretty much identical.

those probably aren't the best examples considering one is 3 phase but you should get the idea

Last edited by gold; 10-10-2009 at 03:17 PM. Reason: added stuff
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Old 10-11-2009, 04:29 PM   #11
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Hey All,

Good thread thus far. I'll be more specific.

Commercial office building:
- CREE LR6: http://www.creeledlighting.com/lr6.htm
- PAR30
- MR16

I understand that commercial buildings are typically wired for 277 V and Residential wired for 120 V.

So there is a CREE 240v. If office building is 277v, then would you need a ballast?
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Old 10-11-2009, 06:52 PM   #12
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That type of adapter would not be subject to 277V. A PAR30 bulb fixture would be connected to a 120 Volt source.

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