Looking for assistance with Fade on Timer for LED Strips

mds82

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Hi Everyone. I am looking for a bit of asssitance in designing a simple and inexpensive circuit. I am looking to run a 24V LED strip to be used for inside cabinet lighting. I currently have the LED strip (http://www.mouser.com/Search/Refine.aspx?Keyword=L219-3080) which is a constant current 24V in 3.75 inch sections. I will be running most likely 5-8 sections inside a cabinet door, with a switch to turn them on when the door opens.

I am looking to design a simple circuit that will fade them on over a 2-3 second period, rather than have them just turn on instantly. there would be up to 10 watts going through the circuit. I know a 555 timer would be the best, just not sure on the rest of the components.

Can someone help recommend the correct parts and a drawing and i an do the rest.
 

delus

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By no means am I a pro, but i have done a few LED strip projects. It seems you're doing things in a very non-standard way.

One of the reasons 24V strips were developed is because voltage drops towards the end of long runs, meaning the LEDs at the end will dim or flicker. With 12V, five meters is as long a strip you can use, but 24V strips are usable ten meters long. So cutting your 24 volt strips to 3.75 inches defeats the purpose of having the extra voltage in the first place.
Also there is a safety issue. 24V is maybe probably possibly reasonably safe in this application, but 12V is a lot safer. This is why 12V is usually used under-cabinet. 12V is definitely bright enough for this application. but 24V would maybe be too bright.
If you are going to have a switch on each door, you're going to need a fade circuit for each switch and strip section, or somehow run spaghetti from each switch to the fade circuit, and back to each strip. Installing all of this inside the cabinet will be a royal PITA. I think there's a reason I've never seen even a picture of LEDs being used on the interior of cabinets. Lots and lots of under-cabinet lights, never interior.
And why do you need a fade in the first place? It's not like the small number of emitters is going to jar you awake.

Won't need much of a power supply for this low a number of emitters. Series would be the preferred wiring.



http://www.instructables.com/id/How-to-fit-LED-kitchen-lights-with-fade-effect/step2/Fader/
 

mds82

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By no means am I a pro, but i have done a few LED strip projects. It seems you're doing things in a very non-standard way.

One of the reasons 24V strips were developed is because voltage drops towards the end of long runs, meaning the LEDs at the end will dim or flicker. With 12V, five meters is as long a strip you can use, but 24V strips are usable ten meters long. So cutting your 24 volt strips to 3.75 inches defeats the purpose of having the extra voltage in the first place.
Also there is a safety issue. 24V is maybe probably possibly reasonably safe in this application, but 12V is a lot safer. This is why 12V is usually used under-cabinet. 12V is definitely bright enough for this application. but 24V would maybe be too bright.
If you are going to have a switch on each door, you're going to need a fade circuit for each switch and strip section, or somehow run spaghetti from each switch to the fade circuit, and back to each strip. Installing all of this inside the cabinet will be a royal PITA. I think there's a reason I've never seen even a picture of LEDs being used on the interior of cabinets. Lots and lots of under-cabinet lights, never interior.
And why do you need a fade in the first place? It's not like the small number of emitters is going to jar you awake.

Won't need much of a power supply for this low a number of emitters. Series would be the preferred wiring.



http://www.instructables.com/id/How-to-fit-LED-kitchen-lights-with-fade-effect/step2/Fader/

Hi Delus, Thanks for the response. The kitchen it brand new and i wanted to go with a nice high quality, high CRI light strip. The power supply is in 1 corner of the room and the LED strips are pretty far away, being used for under cabinet light as well as inside cabinet light. Right now i'm only worried about the inside cabinet ligthing.

Each cabinet will have its own wire going to it, so each segment would need its own fade on circuit, so price is course is a factor. there are about 50 doors and draws in total so that is why price is an issue. In very high end kitchens i have seen where each door will slowly illuminate lights inside the cabinet so you can see in there, and that is what i am looking to replicate. Its just the aesthetics that i am looking for.
 

beanbag

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Jan 7, 2013
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The simplest circuit I can think of is u put a n-ch mosfet (with low R_on) inserted between the negative side of the led strip and power supply, and use a resistor and capacitor (with voltage divider) to charge up the gate.
 
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mds82

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The simplest circuit I can think of is u put a n-ch mosfet (with low R_on) inserted between the negative side of the led strip and power supply, and use a resistor and capacitor (with voltage divider) to charge up the gate.

I'm going to try that actually and see how it works. the LED Strip may not turn on till almost 18 V, so i'm thinking a PWM fade on may be a better choice.
 

beanbag

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ok bad boy, take a look at the LTC6992 - voltage controlled PWM
 
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