Need automatic voltage regulator guidance for simple LEDs in parallel.

Hi All,
I was wondering if anyone could recommend an automatic voltage regulator (booster) for when I add/remove LEDs to a circuit in Parallel?

I currently have a 12v power source with 3A capability going into a 5 x 5mm RED LEDs.

As I add more LEDs (in segments of 5) I notice the lights begin to get dimmer and dimmer.

Is there a module of some sort that allows the voltage to be amplified as it drops to a certain point
Example: 5 Leds (1.8 Vf 20mA) are connected in parallel to 5 more Leds, then 5 more, then 5 more, then 5 more. Then the 3 added LED sets are removed leaving 2 sets of 5 LEDs. Is there a way to automatically increase/decrease voltage based upon the added sets?

A "parallel" example would be the adding and removing of christmas lights together.

Thank you in advance.

-Dats

Sounds like the driver you are using cannot supply enough current as you are adding more parallel strings. The voltage requirement of the driver shouldn't really change as you add more in parallel. If your one strand needs 12V and 1 amp, 2 strings in parallel need 12V and 2 amps. Just get a driver that can source some more current.

With this being said it is not a good idea to run arrays of high powered LEDs with a single driver. Leds, even the same part number, do not have the same forward voltage. This results in an imbalance in the current being pulled for each parallel strand which can cause uneven brightness/heating between strands. The forward voltage drops as temp increases and the current pulled goes up. This forward voltage to temp curve is not the same for each LED either which causes even more of an imbalance.

I'm not saying you can't drive arrays of high power LEDs, it's just better for each series strand to have its own driver.

datspnkrok said:

Hi All,
I was wondering if anyone could recommend an automatic voltage regulator (booster) for when I add/remove LEDs to a circuit in Parallel?

I currently have a 12v power source with 3A capability going into a 5 x 5mm RED LEDs.

As I add more LEDs (in segments of 5) I notice the lights begin to get dimmer and dimmer.

Is there a module of some sort that allows the voltage to be amplified as it drops to a certain point
Example: 5 Leds (1.8 Vf 20mA) are connected in parallel to 5 more Leds, then 5 more, then 5 more, then 5 more. Then the 3 added LED sets are removed leaving 2 sets of 5 LEDs. Is there a way to automatically increase/decrease voltage based upon the added sets?

Click to expand...

Could you clarify your circuit?
With a single string of 5 LEDs connected in series, how is the string connected to the 12V supply - is it via a resistor, or some kind of driver circuit?

uk_caver said:

Could you clarify your circuit?
With a single string of 5 LEDs connected in series, how is the string connected to the 12V supply - is it via a resistor, or some kind of driver circuit?

Click to expand...

Certainly, and thanks for the help. See picture:


I've switched the LED from RED to RGB Tri-color with a common cathode. As a result, the LEDs are in parallel across the board, just split up in 5-LED segments.

I have a resistor connected to the front of the first 5 LEDs. With Vf (R) 1.8 (G) 3.0 (B) 3.0, I have 510, 470, 470 Ohms installed respectively for the first LED, but now there's 5. According to the calculator:

http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator#parallel

I should have 110 R-value attached, and if I go to 10 LEDs, it should be 56 R-value.

I guess I am trying to figure out the most economical and automatic way of compensating for the addition or removal of light segments. It could be via automatic voltage increase/adjustment or via resistor adjustment.

Thanks again for your help, and please let me know if you need additional info.

Cheers,

~Dats

Doogie said:

Sounds like the driver you are using cannot supply enough current as you are adding more parallel strings. The voltage requirement of the driver shouldn't really change as you add more in parallel. If your one strand needs 12V and 1 amp, 2 strings in parallel need 12V and 2 amps. Just get a driver that can source some more current.

With this being said it is not a good idea to run arrays of high powered LEDs with a single driver. Leds, even the same part number, do not have the same forward voltage. This results in an imbalance in the current being pulled for each parallel strand which can cause uneven brightness/heating between strands. The forward voltage drops as temp increases and the current pulled goes up. This forward voltage to temp curve is not the same for each LED either which causes even more of an imbalance.

I'm not saying you can't drive arrays of high power LEDs, it's just better for each series strand to have its own driver.

Click to expand...

Yes, I agree with you on the driver, but at 20mA, I shouldn't I be able to put A LOT of LEDs on this thing before I see a drop. 12 volts is still registering across the board, which is nice. But 10 LEDs @ 20mA would only pull .2 amps right, so my 3A should be good.

I think it may be my conductors. I ripped apart a Cat-5 network cable because I needed 12 small wires ( 3 strands of RGB diodes, so 12 wires total) The gauge on a cat-5 is 24, very small!

I do need to bundle 12 wires together and at the lengths I would want to possibly add: 20 ft, 50ft, 100ft??, sites are recommended 18 gauge Do you think I can get away with 22 gauge?

12 of these wires bundles is going to be pretty thick.

Thanks again for all your help.

~Dats

datspnkrok said:

I guess I am trying to figure out the most economical and automatic way of compensating for the addition or removal of light segments. It could be via automatic voltage increase/adjustment or via resistor adjustment.

Click to expand...

The simplest way would be to supply neat 12V power to each segment, with resistors on each segment to control the power going to its own LEDs.
With the resistors upstream of all the LEDs, all the segments are sharing the same ~100mA total.

If the physical layout was like the diagram, with segments effectively daisy-chained off each other, you'd need to move a set of resistors onto each board, disconnect the output connection of a segment from the internal 'bus', and connect it directly to the 'raw' input power connection.

Like this:

uk_caver said:

The simplest way would be to supply neat 12V power to each segment, with resistors on each segment to control the power going to its own LEDs.
With the resistors upstream of all the LEDs, all the segments are sharing the same ~100mA total.

If the physical layout was like the diagram, with segments effectively daisy-chained off each other, you'd need to move a set of resistors onto each board, disconnect the output connection of a segment from the internal 'bus', and connect it directly to the 'raw' input power connection.

Like this:

Click to expand...

Thanks UK_Caver, that is a perfect description and understanding how I can design the resistors for 5 LEDs on each leg and just plug them in, not worrying about dimming as I add more LED segments (boards). However, if I want to do a daisy-chain, similar to Christmas lights, I am now running twice the number of conduits.

I think my original design was because I minimized the number of conduits moving through everything. With the common Cathode, I would just tap into the existing hot (with 3 RGB grounds) and continue along the daisy chain. With your cleaner version, and the "Christmas light daisy-chain" I need to bring that clean 12v power to the other end of the wires, resulting in 8 wires instead of just four along the strand. Did I clarify this correctly?

Is there a method to reduce the number of conductors or consolidate them? What if I just run an extra hot and daisy chain the grounds, considering that's what controls the RGB anyway<-- realized this would send current through that first resistor, so this would not work, or it would be back to my original design.

Thanks again.

~Dats

Just a quick note regarding the 12v power. One way it seems like the 12v power can be daisy chained directly, but the RGB grounds would need to be separated, thus there would be 3 extra RGB conductors running along in parallel with the +12v & RGB grounds hooked up to lights, totaling 7 (not 8).



~Dats

You're right about the common wire not needing to be duplicated.

As far as wire thickness is concerned, don't forget that the common wire might be carrying 3x the current of the other wires (if R,G,B might all be on at the same time), and so if you were going for minimum total wire weight you might want to make the common wire thicker than the others.

The way to minimise wiring would be for each LED to have its own set of resistors, running off the 'raw' power lines.

Thanks UK Caver,
I am assuming that would still be worth the extra resistor design considering the cost of copper?

I'm going to update my schematic then send it your way.

Thanks again.

~Dats