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schematic

simulate this circuit – Schematic created using CircuitLab

So from the start what Im trying to achieve is drive way lighting in which each colour is separately dimmable with a pulse width modulator so I can achieve what ever colour is desired each PWM is capable of outputting 8A Ive chosen to protect each of them with 10A Circuit breaker as I have plenty lying around and I dont want them tripping under a consistant 8A load.

So from a 240v ac supply in to 12v 30A dc. From this 12v 30A supply to my circuit Ill protect each Pulse width modulator with a 10A circuit breaker

From each of these circuit breakers a direct connection to a current monitor with digital display so I know how much from 1-10A im supply each line of SMD LED's

From each current monitoring lcd I will connect SMD LED in parallel to the continually running supply.

Each of the 3 supplies (red active one) (Blue active two) (green active three) one for red one for green and one for blue will continue to feed right to the end cluster of 3 smd led's.

Two questions that cross my mind inititally one, can a pulse width modulator share the same return neutral I mean as the current is being chopped up to provide lower levels of light for each one should it matter that three differently chopped up sections of power meet to flow back? Seens these three originated from the same place didnt validate to me as a valid argument its ot like they are out of phase tho its dc?

Two a particular smd led i was looking at seems to be a straight forward connection 6 terminals three at either side you would simply bridge three at one end connect them to positive and the three at the other end to neutral and you would do this for each colour and do i need resistors for these as the website doesnt state.

I originally looked at RGB smd led's but they share the same active and seperate return neutrals in which case a PWM would not work as it needs to interrupt the supply to the led's.

and i guess my final question is would this work if the 1st two are a yes? If it would work is there an easier way to achieve the same task? I originally wanted to use a DJ styled sliding switch to modulate the intensity of each colour individually (one switch for each colour) and use premade clusters that i could wire up a supply to each colour red, green and blue. However after learning the active is shared that wont work.

Im kinda stuck I hope the message of what im trying to achieve gets across? Basically 240v a.c supplying my driveway and foot path lighting in which I can control the level (brightness) of green, red and blue individually whilst still maintaining this system to be as reliable as possible. (and the main aim of making a system I would like to buy or make which ever is necessary extra led cluster or which ever configuration i end up with so in the long run should one blow I can simply replace it, also should one blow it will not effect the rest of the circuit that being the reason its all in parallel.

EDIT

schematic

simulate this circuit

Im not sure common cathode would work due to how they are wired internally sharing one neutral would force you to wire them up as i interpret the only method i could think of as parallel in which case i think you would need a resistor on each led so 9 resistors per fitting?

as you mentioned laying out my questions more simply I apologize for my previous question I probably should have relayed it out instead of typing it as the thoughts came to me so ill try now.

Question: Does this looks as if with a common cathode i will now require 9 resistors per fitting because the only possible way to wire them is parallel?

Question: Will using 3 red smd in series, 3 blue smd in series and 3 green smd in series produce mixed colour as intended?

resistor Red Red Red resistor Blue Blue Blue resistor Green Green Green positioned physically like this? I could imagine the colour would be as consistant as a RGB led but it should work logically?

Question: Is it possible to wire the common cathode ones using 3 resistors or does it now look more logical to use 3 of each colour physical size should be in total than 19x19mm given they are each 5x5 I would have 9 in total and would like a 1mm gap between each.

circuit diagram for common cathode

Datasheet for common cathode

my attempt at laying out how they would physically look was thwarted by the scripts, basically 3x3 square top line red middle line green bottom line blue

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  • \$\begingroup\$ I just noticed there is an error on the 1st set of led's the green one does not goto neutral but continues along and on the second set it seems i have mistakenly switched blue and green around. \$\endgroup\$ – Muteki89 May 27 '14 at 10:54
  • \$\begingroup\$ ebay.com/itm/… the current monitoring lcd display in question \$\endgroup\$ – Muteki89 May 27 '14 at 11:08
  • \$\begingroup\$ ebay.com/itm/… the pulse width modulator in question \$\endgroup\$ – Muteki89 May 27 '14 at 11:08
  • \$\begingroup\$ ebay.com/itm/… the tpye of smd led im thinking about the red is 2.2-2.4v would i need 5 in series to bring it up to 12v with no resistor, the green and blue are 3-3.6 and 3.4-3.6 respectively would i need 3 of each of these to get to 10.8v and a resistor in series aswell to chew up the remainder? Ideally i wanted just one of each of these as i figure for simple 700mm spacing three of these led's will probably achieve a reasonable amount of accent style lighting. \$\endgroup\$ – Muteki89 May 27 '14 at 11:09
  • \$\begingroup\$ Their purpose isnt to see your way through the dark but if they were all on im assuming these would put out enough light with them 700mm apart for you to be able to see reasonably well. \$\endgroup\$ – Muteki89 May 27 '14 at 11:10
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Your "question" probably has most of the information required to 'get going' BUT it is very hard to read. Some people have trouble extracting questions out of such a complicated mixture and may vote to close the question rather than trying to understand it. Making the actual questions as clear as possible will help others to help you.

Can a pulse width modulator share the same return neutral

Yes, you can have a singe common conductor. This needs to be of low enough resistance that current changes from one colour do not produce so much change in voltage drop in the neutral lead that it affects the voltages that the other colours "see".

A particular smd led i was looking at seems to be a straight forward connection 6 terminals three at either side you would simply bridge three at one end connect them to positive and the three at the other end to neutral and you would do this for each colour

You need to look at the data sheet or see how they are connected internally by testing. In many cases such arrangements are indeed 3 independent LEDs and you can parallel them by connecting all the pins on a side together, as you suggested.
While ideally you DO need a resistor for each LED in such an arrangement, in practice the 3 LEDs within a single package are closely matched and may be "hard paralleled" without too much imbalance. Note that LDDs in different packages are NOT likely to be well matched and each group of 3 LEDs in the one package usually needs a resistor.

And do i need resistors for these as the website doesn't state.

You say "the website" -> please provide as much information as possible including links to datasheets and associated material. See above re needing resistors.

I originally looked at RGB smd led's but they share the same active and separate return neutrals in which case a PWM would not work as it needs to interrupt the supply to the led's.

You can probably find tricolour LEDs with common Cathode if you look for them.

and i guess my final question is would this work if the 1st two are a yes?

You seem to be describing using 3 strings of coloured LEDs, all LEDs in a string parallel connected and each LED or group of 3 in pkg having its own resistor. So - YES such an arrangement would work if done properly.

If it would work is there an easier way to achieve the same task?

What can be easier. The system you describe is very simple. You could use linear feed but that would be less energy efficient.

I originally wanted to use a DJ styled sliding switch to modulate the intensity of each colour individually (one switch for each colour) and use premade clusters that i could wire up a supply to each colour red, green and blue. However after learning the active is shared that wont work.

As above. Find common Cathode RGB LEDS if you wish to have them combined.

However - you can but RGB LED strips - usually designed for 12V operation. These are liable to cost less per LED than a system that you build yourself.

Im kinda stuck I hope the message of what im trying to achieve gets across? Basically 240v a.c supplying my driveway and foot path lighting in which I can control the level (brightness) of green, red and blue individually whilst still maintaining this system to be as reliable as possible. (and the main aim of making a system I would like to buy or make which ever is necessary extra led cluster or which ever configuration i end up with so in the long run should one blow I can simply replace it, also should one blow it will not effect the rest of the circuit that being the reason its all in parallel.

More soon ...

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  • \$\begingroup\$ Thanks for all the information I did look at 12v strips of smd led's as it crossed my mind that the work of finding suitable resistors for each led has been done. This would probably be the easiest method all i would have to do is buy a red, blue and green roll individually and cut them on the cut lines usually 3 smd led's in each section. I will look into "common Cathode RGB LEDS" as this information may lead to a better end result and smaller workload not as much soldering \$\endgroup\$ – Muteki89 May 28 '14 at 8:05

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