 Subaru1-3-2-4Premium
join:2001-05-31
Greenwich, CT
1 edit | Dimming a LED strip I have some white LED's mounted behind my 40" tv anyways when watching a movie it's just a tad too bright since I went around the whole screen.. The only thing is it's only like 100K so I don't know how dim it will go if at all. The voltage being supplied is 12V @ 1A
hmm I forgot I have a 555 timer I picked up last month but can it be used for fade in to fade out? |
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| said by Subaru:I have some hite LED's mounted behind my 40" tv
How many? In what configuration?
The only thing is it's only like 100K
Personally, first I'd start with a minimalistic approach by trying various power supplies that supply less than 12V/1A. (I have a cardboard box with at least 2 dozen wall warts)
After that, I'd try to find a suitable series resistor, possibly a small light bulb, especially if the resistor need to be over a watt.
Yes, you can make a PWM circuit with a 555, but you may need an external transistor, depending on the current.
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Wacky Races 2012! |
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Subaru1-3-2-4Premium
join:2001-05-31
Greenwich, CT | I would have to count them but I'm about to head to bed.. it's in parallel.
I brought up the PWM because I thought it would be neat to have them fade out when the power is turned off and fade in when the power is turned on.. having said that the brightness needs to be cut a bit since it's a bit too bright.. I'd have to count them after work since it involves moving the tv around. |
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Subaru1-3-2-4Premium
join:2001-05-31
Greenwich, CT | reply to Subaru
well Im home but one thing before I count what about a R-C plus a fet?
I count 151 LED's |
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| 151 LEDs? How are they configured? I'd think 50 segments of 3 LEDs, but that comes out to 150. In any case, with that many, no surprise it's too bright! 
Yes, you can also use a FET with some RC delay.
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Wacky Races 2012! |
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Subaru1-3-2-4Premium
join:2001-05-31
Greenwich, CT | How are they configured? it's like 3 LEd's to a strip.. which is able to be cut then with wires connected back together. |
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iknowPremium
join:2012-03-25 | reply to Subaru
Re: Dimming a LED strip said by Subaru:I have some white LED's mounted behind my 40" tv anyways when watching a movie it's just a tad too bright since I went around the whole screen.. The only thing is it's only like 100K so I don't know how dim it will go if at all. The voltage being supplied is 12V @ 1A
hmm I forgot I have a 555 timer I picked up last month but can it be used for fade in to fade out?
$100K in L.E.D.s?? for that price, the controller should have been included!. |
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Subaru1-3-2-4Premium
join:2001-05-31
Greenwich, CT | I was referring to the resistor |
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 SparkChaserPremium
join:2000-06-06
Downingtown, PA
kudos:3
 ·Verizon FiOS
| said by Subaru:I was referring to the resistor
It's going to take a lot (8000+) to get 1A from 12V with 100K resistors.  |
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Subaru1-3-2-4Premium
join:2001-05-31
Greenwich, CT | reply to Subaru
Re: Dimming a LED strip heh so in my case I would be doing a monostable circuit right?
The power adapter which powers the LED's is plugged into an outlet controlled by a switch so I flip the power on and it dims (lets say 7 secs) to full brightness but with the resistor in not as blinding as before.
And when the power is cut it should fade within 7 seconds or so? |
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| When the power is out it will fade in less than a second, I can guarantee that, unless you put in a supercap or two.
Of course 0.1s is less than 7 seconds... 
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Wacky Races 2012! |
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Subaru1-3-2-4Premium
join:2001-05-31
Greenwich, CT | with the lights as is now it glows for a bit when I turn it off but it's quick.
i'm going to try a monostable design when I have enough time besides I don't have a transistor here I wonder if I could use a mosfet instead? |
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iknowPremium
join:2012-03-25 | said by Subaru:with the lights as is now it glows for a bit when I turn it off but it's quick.
i'm going to try a monostable design when I have enough time besides I don't have a transistor here I wonder if I could use a mosfet instead?
the Mosfet is actually better for this use, it needs virtually no current to switch dc, because of the high gate impedance, and it's immune to thermal runaway. |
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Subaru1-3-2-4Premium
join:2001-05-31
Greenwich, CT | hmm interesting.. one person was suggesting I use two Smitt Triggers along with a transistor to control it. |
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iknowPremium
join:2012-03-25 | said by Subaru:hmm interesting.. one person was suggesting I use two Smitt Triggers along with a transistor to control it.
transistors are cheaper and more widespread, that's why. |
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Subaru1-3-2-4Premium
join:2001-05-31
Greenwich, CT
1 edit | reply to Subaru
This is what they came up with but I don't know.. 4 schmitt trigger seems excessive for a simple fade on/ fade off?
The bubbles on the trigger outputs I'm not 100% sure what that means. |
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 shdesignsPowered By Infinite Improbabilty DrivePremium
join:2000-12-01
Stone Mountain, GA | You don't need the transistors to drive the MOSFET. you can parallel the schmitt inverters (the bubbles say it is an inverted output). |
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iknowPremium
join:2012-03-25 | reply to Subaru
said by Subaru:This is what they came up with but I don't know.. 4 schmitt trigger seems excessive for a simple fade on/ fade off?
The bubbles on the trigger outputs I'm not 100% sure what that means.
you need one to debounce the switch, and generate the on delay, one to generate the off delay, and the 2 in series preserves the polarity, since they are inverting, luckily, schmitt triggers come 6 to an I.C., so you only need one package. the transistors would only be needed if you switched high current in the kilohertz range, for your application, it's essentially D.C. so the gate impedance would be in the megohms. |
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