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#1
02-24-2009, 06:21 PM
 fearnofish420 New Member Join Date: Feb 2009 Posts: 8
Best way to DIM Led Strip?

I need to be able to Dim 2 Led Strips that I have connected to a 12v Battery. I was wondering what is the most efficient/simple way to achieve this? If anyone could possibly point me in the direction to a schematic or a type of circuit that would be able to preform this operation.

Thank You to anyone with some input!
#2
02-24-2009, 06:47 PM
 bertus Administrator Join Date: Apr 2008 Location: Amsterdam,Holland (GMT + 1) Posts: 12,289

Hello,

Have a look at this thread where SgtWookie made a simple PWM circuit.

Greetings,
Bertus
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#3
02-24-2009, 06:56 PM
 italo Banned Join Date: Nov 2005 Posts: 205

LEDS are not exactly linear devices a minimn voltage must be present and a minimumn current must flow. Having point that out the best way to control LEDS are by controlling the current. If you controll the current then the voltage requirement is immaterial. the best chip to do that cheap and easy is the lm317 1.25 v voltage regulator. the design is simple assume a max current of whatever the LED can sustain withing the power consumption and add a resistor 50Ω [20 ma] and a pot of 50 Ω [1.25 ma] in series from adj to output. These value are examples of current. Too complicated then measure the voltage source and add a variable resistor in series that will get the same results.
#4
02-24-2009, 10:09 PM
 SgtWookie Expert Member Join Date: Jul 2007 Location: In the vast midwest of the USA; CST Posts: 22,043

Quote:
 Originally Posted by italo LEDS are not exactly linear devices a minimn voltage must be present and a minimumn current must flow. Having point that out the best way to control LEDS are by controlling the current. If you controll the current then the voltage requirement is immaterial. the best chip to do that cheap and easy is the lm317 1.25 v voltage regulator. the design is simple assume a max current of whatever the LED can sustain withing the power consumption and add a resistor 50Ω [20 ma] and a pot of 50 Ω [1.25 ma] in series from adj to output. These value are examples of current. Too complicated then measure the voltage source and add a variable resistor in series that will get the same results.
I really wish that you would stop replying to threads until you know what you are talking about.

The "information" that you have provided is very easily misleading and potentially very confusing to newcomers.

If the original poster's LED "strips" are rated for operation at 12v, they will not work with an LM317 regulator configured as a current regulator. In such configuration, LM317's have a minimum 3v drop from input to output, which would prevent our OP's LEDs from lighting at all.

Most LED ropes or "strips" rated for 12v have built-in current limiting or regulating circuits. For this particular application, PWM is clearly the way to go.
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#5
02-24-2009, 11:25 PM
 fearnofish420 New Member Join Date: Feb 2009 Posts: 8

There is so much information on PWM and 4093 Schmitt input NAND gate. Where is a PWM schematic that I would be able to replicate to create an led dimming circuit?
Thanks for all you help and patience with me. Believe it or not I actually graduated recently as an electrician but very little was taught about electronics and PWM. I understand the 555 timer but as far as other parts needed to make it work that I am not sure of.
Thanks again to all
#6
02-24-2009, 11:48 PM
 fearnofish420 New Member Join Date: Feb 2009 Posts: 8

This is what I have made and It does not work. All that happens is the light strip pulses extremely fast. I move the potentiometer very minimal and only see it fluctuate its pulse. Nothing dims what so ever. I have put this circuit onto a breadboard and have tried to make it dim with no results I dont know if its the values I have or the wrong type of components but your knowledge is greatly needed. If it helps anyone figure this out I used electronics workbench to create this schematic.
Attached Files
 pwm.doc (38.0 KB, 37 views)
#7
02-25-2009, 02:21 AM
 hgmjr Super Moderator Join Date: Jan 2005 Location: Tennessee, USA (GMT-6) Posts: 9,030 Blog Entries: 11

Before you go any further with your design you need to calculate a current limiting resistor to put in series with your LED. Otherwise the LED and/or the transistor will be damaged.

hgmjr
#8
02-25-2009, 03:23 AM
 SgtWookie Expert Member Join Date: Jul 2007 Location: In the vast midwest of the USA; CST Posts: 22,043

This thread is basically a duplicate of a thread in the Projects Forum:

I've responded in the other thread about inconsistencies in our OP's schematic; in particular the mislabled 555 timer pins, and posted a circuit using a 555 timer that should do what our OP wants to do.
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 Tags dc voltage, dim, dimming, led, led strip, strip

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