# Thread: Seoul p4 and 5mm LEDs in the same circuit, is it possible?

1. ## Seoul p4 and 5mm LEDs in the same circuit, is it possible?

Hi,

I'm brand new here
I've been fooling a bit around with LEDs for my terrarium setup, and got quite good results, if I should say so
But now I'd like to do a little more by making a lamp, combining high power, and regular 5mm LEDs. I just can't seem to find any info on this, so I'm starting to worry that it's not even possible...
This is where I hope You guys might come in to the picture, cause I don't really know anything about circuits

Well, the setup I'm working ons should consist of:
One seoul p4
and 10-15 5mm LEDs in different colors.

The p4 should only be run at 350 mA, since I won't be able to give that much cooling.
My question is then: Is possible to have both the p4 and the 5mm LEDs in one circuit running on a 350 mA constant current power supply, by adding resistors, or connecting the 5mm's parallel?

Please forgive my n00b question I hope You guys can help!

Christian

2. ## Re: Seoul p4 and 5mm LEDs in the same circuit, is it possible?

I just did a quick attempt at drawing a possible circuit here..

It consists of:
The one Seoul p4 (Vf = 3,2V)
Ten blue 5mm LEDs (Vf = 3,5V)
Five Red 5mm LEDs (Vf = 2,4V)

The constant current driver puts out 350 mA, which should equal to roughly 23 mA running through each of the 5mm LEDs.

Would this setup work?? Or should I put resistors on the red 5mm LEDs? This is where my lack of knowledge sets in..

Christian

3. ## Re: Seoul p4 and 5mm LEDs in the same circuit, is it possible?

that's a tricky situation, I would say put everything in parallel then add resistors to each LED that requires a voltage lower than the highest Vf. You might be better off using a simple low current low voltage transformer.

4. ## Re: Seoul p4 and 5mm LEDs in the same circuit, is it possible?

If yoy connect them according to your diagram the red leds will receive 70mA each, and the blue will not light at all.
If you add 56 ohms resistors to each red led they will receive 20mA each, but the blue leds may deviate between 5mA to 40mA due to induvidual Vf.

I would have added 68 ohm resistors to each red led, and added 10 ohm resistors to each blue led. Then I would be confident they receive 20mA each.

Remember R=U/I, where I is 0.020A.

5. ## Re: Seoul p4 and 5mm LEDs in the same circuit, is it possible?

Thank you guys for the pointers

I think I understand how to calculate those resistor values..

So that was the first step on the way.. The real plan for my project is actually to have five highpower LEDs all surrounded by two blue and one red 5 mm LED like this:

Would I then just be able to do like this:

In this case the constant current power supply should be 1,75 A I guess? (5 * 0.350 mA), but will I be able to adjhust this to 20 mA over the 5mm LEDs? Or do I need 87 5mm LEDs, for them to split up the 1,75 A into 20 mA for ewach LED? (As you can hear, I don't really know if a resistor can also adjust the current...)
I put the p4's in parallel, to avoid total black out if just one fails, but will it stress the others to much if one should pop??

I really appreciate Your help! As you can see I'm REALLY not familiar with this circuit business.. But I'm eager to learn :P

Christian

6. ## Re: Seoul p4 and 5mm LEDs in the same circuit, is it possible?

Korxi,

I wouldn't recommend having your 5mm LEDs in series with your power LEDs. It is very tricky to set up, and I do not know if it would be easy to get each LED running at a happy 20mA.

First of all, do you have a certain voltage coming from a power supply (we know the current is 350mA)? Have you even planned which power supply that you want to use? I would recommend finding a power supply that will give you enough room (max current handling wise) before you decide which LEDs you want to put in series and which in parallel.

Though, theoretically, your setup of having all your 5mm (in parallel) hooked up in series with your power LEDs could work. However, in the real world, where there are many different variables of forward voltages and resistances, that set up would not be ideal.

Remember that everything in series will share the same current, but split up the total voltage, while when everything is in parallel, the current is split up between each device (not always evenly), and every device will see the total voltage of the supply. I see that you understand that LEDs have a forward voltage, where at that voltage, an exact current will be drawn. I noticed that you have identified the difference between the red and blue and power LEDs. Good! Finally, do not forget that these forward voltages are just approximations for that type or model number of LED. In the real world, each LED that you have will have its own different forward voltage at a certain current level.

This is why LEDs can be tricky to use. One power LED (#1) may have a forward voltage of 3.2V at 350mA and 3.5V at 700mA. The next LED (#2 - soon to be in parallel with LED #1) may have a forward voltage of 3.28V at 350mA and 3.6V at 700mA. Your constant current driver circuit works by varying the voltage (very instantaneous) until the programed current is drawn. Lets say that this nice regulated current circuit is programed to deliver 600mA. With LED #1 and LED #2 in parallel, each will get its cut of the 600mA of current. LED #2 will require at 350mA a voltage of 3.28V, while LED #1 only needs 3.2V. The circuit will sense that both will need around 2.2V or so, and that is what it may deliver. LED #1 will be happy with this voltage and draw 350mA. However, LED #2 will run at a lower current than 350mA because the voltage is not 3.28V. Instead, LED #2 may only run at only 250mA. Therefore, LED #2 will appear dimmer and run cooler than LED #1. Most likely, you will not be as happy as LED #1 is.

Now, lets put both LEDs in series instead of parallel. Lets see, the forward voltages will add up, and both LEDs will receive exactly 700mA each in this case. The power supply will sense that more voltage is needed to regulate this 700mA than before, so it will adjust accordingly. The Vf of LED #1 plus the Vf of LED #2 is 7.1V. Therefore, each LED will get its happy 700mA each, as long as the driver circuit can regulate their combined forward voltages.

Running multiple power LEDs in series is usually the ideal method. The current draw of a power LED can vary dramatically with a small change in Vf, compared to a lower power 5mm LED, where the current would not vary as much.

Really quick, check this out. This is a link to someone who has measured the Vf of a particular LED when the current was programmed at a certain point. It is in the form of a easy-to-read graph:
http://www.candlepowerforums.com/vb/...d.php?t=169547
Just scroll down a little on the first post and look for the graph called “Forward Voltage”. It compared several various power LEDs. These may not be Vf values that you should go by exactly, but they should be closer than what the vague range found in a datasheet may show. This is just an example. I can provide more links later of more LED types. As for 5mm LEDs, the Vf will be considerably lower.

Resistors could work like individual current control devices, but they are less precise (due to the set values), and the amount of current that passes through them depends on the voltage. In order to run LEDs #1 and #2 in parallel, with each LED having its own series attached resistor, then the values of each resistor would have to be different. For the small difference in Vf of the LED to operate at 350mA, then each resistor will have to have slightly different values of resistance. One value of 4.7 ohms may be really common, but a value of 4.85 ohms may be more difficult to find (unless you stack resistors). In addition, the resistors burn off the chopped current as heat, which means lower overall efficiency of the circuit.

A current regulator will have its own range of input and output voltages that it can tolerate. Running them at above or below these ranges will result in unsatisfactory results, or even damage to one of your components. If the input voltage range is higher than the output range, then the circuit is a buck mode regulator. If the input voltage range is lower than the output voltage range, then the circuit is a boost mode regulator. This is why I asked what power supply you plan on using. With a common 12V power supply, and the appropriate driver (maybe a buck regulator), you can run a maximum of 3 power LEDs, or maybe 4 power LEDs (if the Vf of each is low enough) in series. However, if you get a voltage boosting current regulated circuit, you can possibly fit 4 to 7 power LEDs in series.

Remember that (Vin * Iin) * (Efficiency of circuit) = (Vout * Iout). This applies to any type of regulating circuit that you use. You will find that many regulators also have a maximum current input handling, and a maximum current output. Each circuit also has a unique efficiency. Lower quality regulators may have efficiencies in the upper 70% range, while a nice regulator may have a an efficiency in the 90% area. The efficiency will also vary, depending on the Vin and Vout difference, as well as the type of circuit (buck, boost, buck/boost).

Sorry if you know this stuff already. I thought that anyone fresh to using LEDs in projects should know more. There are many finer details, and my examples were pretty vague, but hey, I was just trying to get the point across.

What would I recommend? Well, if I were doing this, I would have a few separate circuits running off the same power supply.
Let’s see. This is what you desire, right? I will make my recommendations based on the above diagram. Actually, I might change it around some to possibly make it easier for you (design wise).

First, you may need to keep your Seoul P4s separate from the weaker 5mm LEDs. I think that if you had a few in series, running off of a basic 12V power supply, then everything would be simpler. You can have three Seoul P4s in series running off of a basic buck mode circuit, then have another set of three Seoul P4s running off of another similar buck circuit. Then you can have one or two separate strands of blue 5mm LEDs in series running off of a basic resistor, and one last strand of red 5mm LED running off of its own resistor. Wait, resistors in a circuit like this? Sure. The current draw is little, as is the amount of power wasted as heat (insignificant), and the voltage from the power supply is relatively constant, so the current going to each 5mm should not change very much.

You will need a 12V power supply that can handle the current (later on that), and a few current regulators. Here is one you could use (here: http://www.kaidomain.com/WEBUI/Produ...px?TranID=2982), however, it outputs 750mA of current. You can change the little surface-mount resistor on the circuit board to change the current to 350mA (change the 0.27ohm resistor to something close to 0.57ohm -www.mouser.com has a bunch of cheap current sense (programing) resistors with funny values close to this). You can find the resistance values by using an online resistor calculator like this one:
http://www.luxeonstar.com/resistor-calculator.php
Just enter the supply voltage, the total Vf of the series-connected LEDs, then enter the desired current amount. Then you have yourself a value for that resistor that you will need.

Here is something I drew up. You need enough strings of blue and red LEDs to meet your needs. You probably cannot have more than 3 series connected blue emitters for a 12V supply, and no more than 4 series connected red emitters. You can have 1 or 2 in series in a string; you just need a slightly larger resistor value to compensate. The resistor value calculator will help you.

You may get away with hooking two 5mm LEDs in parallel, then hook 3 of these couples in series, just use the right resistor value. As for the Seoul P4s, you can use just two in series (so you have 5 total) if you use a flexible current regulator like the one mentioned above.

I hope this helped you more than confused you. There is a lot to getting LEDs to operate at proper conditions, and even more when combining power LEDs and low-power LEDs of different colors. If you want to better understand a circuit, then sketch up any ideas, then simulate what may happen at each point in your head. Once you begin building off a plan, you get to know your plan very well!

Good luck. I better get back to my work. I keep getting distracted ha ha ha (look at all above)!

-Tony

7. ## Re: Seoul p4 and 5mm LEDs in the same circuit, is it possible?

Wow Tony! Thank you so much for taking the time to do that reply, and helping the newbie here..

I do believe I understand most of what you wrote - at least I get the point.. I've been reading alot about circuits and so on these last couple of days - and god knows how many LED tech. sheets if scrolled through!

I don't really know why I got so fixed on the constant current power source.. Perhaps it's because that's what I've been using for my terrarium.

I think I'll have to read through your reply a couple of times more, and then think up a plan. My thoughts now goes along the lines of exchanging the white Seoul p4's with hyper-bright white 5mm LEDs .. Nichia or something, that would make matters a whole lot easier!

Again, thank you for taking the time!

Christian

8. ## Re: Seoul p4 and 5mm LEDs in the same circuit, is it possible?

Do not be afraid of using high power LEDs. Trust me when I say that they are easy to work with, and very hard to totally screw up. I realize now (that I understand how to properly operate power LEDs) that I was terribly abusive to the old Luxeon I and Luxeon III when I was younger. I preferred direct drive in most my lights, pushing more than the current that the LEDs are rated for. I only killed a few (by total stupidity or clumsiness). Today's LEDs are more rugged (both electrically and mechanically). The Cree XR-E and Lumileds K2 are tough buggers! It is hard to just kill an LED (to go pop). They just die super slowly if the abuse is continuous. Actually, typical 5mm LEDs are more frail electronically since it is easy to send too much current to them.

The Seoul P4, when running at low currents, put out large quantities of light. I worry that you may not be totally happy with a bunch of cheap, blue-ish white LEDs from ebay. The converter circuits are easy to find, and also cheap. I can help you find more later. There are also less connections to bother with (less soldering and you do not need a huge circuit board for the little through hole LEDs).

For fixed lighting, you can run your Seoul P4s with a resistor, for even more simplicity. It is not a flashlight, so extreme efficiency is not needed. Finally, with a different power supply (with higher voltages), you can use more LEDs in one string, and use less converters or resistors. For example, a 18V, 24V, or even 32V wall wart can be used (ones for laptops, or wall warts for printers). Well, "quicky" post? Yeah right! Gotta go...

-Tony

9. ## Re: Seoul p4 and 5mm LEDs in the same circuit, is it possible?

Would there be any benefits in using an AC power supply, and then just assemble each of the five "lamps" with a rectifier in front? If so, will I then also have to have a current regualtor on each lamp for the one seoul p4?

If this is possible, I'd assemble each of the five lamps on a PCB, and then they'd be like little bulbs that could easily be changed if/when one fails (and since they wouldn't be in series, the entire thing wouldn't die if just one of them fail!) .. Maybe I'm getting ahead of myself again now ...

Christian

10. ## Re: Seoul p4 and 5mm LEDs in the same circuit, is it possible?

I'll come right out and say it first that my knowledge and digestion of electronics is uber suck.

However an idea you might want to look at is to water cool the LED's by using some thin copper piping and running it on top of the heatsink of the LED's. Using say some JB Weld adhesive to bond the piping to the heatsink then hook the open end of the copper pipe to the waterpump.

It has been a long time since I've owned an aquarium. I do believe you'll need to make your own 'Y" split adaptor so one open end of the "Y" is in the fish tank to uptake the water back into the pump.

Just an idea which could keep the LED's nice and cool and you can bump up the brightness for the tank friends as well and not worry about overheating the LED's. If it's tropical fish I would think you'll be also helping to save a bit of the heating element in the heater by water cooling the LED's at max brightness while putting that heat back into the water.

11. ## Re: Seoul p4 and 5mm LEDs in the same circuit, is it possible?

Originally Posted by Zero_Enigma

However an idea you might want to look at is to water cool the LED's by using some thin copper piping and running it on top of the heatsink of the LED's. Using say some JB Weld adhesive to bond the piping to the heatsink then hook the open end of the copper pipe to the waterpump.

It has been a long time since I've owned an aquarium. I do believe you'll need to make your own 'Y" split adaptor so one open end of the "Y" is in the fish tank to uptake the water back into the pump.

Just an idea which could keep the LED's nice and cool and you can bump up the brightness for the tank friends as well and not worry about overheating the LED's. If it's tropical fish I would think you'll be also helping to save a bit of the heating element in the heater by water cooling the LED's at max brightness while putting that heat back into the water.
It's unlikely that you'll find a lot of water to cool the LEDs in a terrarium.

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