Help for design simplest circuit for 6*1wat white LED in parallel(LED Driver) - Page 1
Forum section: electronics / beginners

author: rozeh
author_rank: Regular Contributor
timestamp: December 01, 2013, 12:43:33 pm
content: Hi everybodyI'm doing a project to design a circuit. I have to connect 6 number of 1wat white in parallel. this circuit will work on a ship with 24v supply. Do you have any idea for making it very simple? I already saw this:Super simple high power LED driver

author: GK
author_rank: Super Contributor
timestamp: December 01, 2013, 12:59:26 pm
content: Here is the LED display power supply I designed for my discrete digital clock project. My displays have almost 200 10mm LED's in total each with a nominal V drop of 2V. I run a 100R series dropper on each from the regulated 3V. Overall it is relatively efficient.I think it's pretty simple and straight forward.

author: rozeh
author_rank: Regular Contributor
timestamp: December 01, 2013, 04:51:18 pm
content: Thanks dear GKI think it's a bit complex for me.What is your opinion about this circuit?:

author: mariush
author_rank: Super Contributor
timestamp: December 01, 2013, 05:16:12 pm
content: a waste of money and chips?What do you guys have against led drivers ?1w led ... 2.8-3.4v voltage 1w .. that's about 300mA ... times 6 is about 19-20v ... so 19v 300mA ... no problem driving a led driver from 24 volts. Get a buck led driver and you're done. Or get two and put just 3 leds on each led driver... they're cheap at about 1$ eachPut the leds in series and get one of these :http://uk.farnell.com/zmdi/zled7000-zi1r/led-driver-buck-0-75a-sot89-5/dp/1898426RLhttp://uk.farnell.com/zmdi/zled7000-zi1r/led-driver-buck-0-75a-sot89-5/dp/1898426http://uk.farnell.com/diodes-inc/ap8801sg-13/ic-led-driver-buck-0-5a-8sop/dp/1825358

author: GK
author_rank: Super Contributor
timestamp: December 01, 2013, 11:47:45 pm
content: Quote from: rozeh on December 01, 2013, 04:51:18 pmI can't see that working with those 20k resistors in series to the regulator inputs, even in the simulator. You probably should be looking for a dedicated LED driver IC as already mentioned. A switching one too otherwise with a 24 supply you will be dissipating a lot of power in the regulator(s), and especially so if you insist on connecting the LEDs in parallel instead of series.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 02, 2013, 12:02:17 am
content: If you have 24V available you really want to wire them in series, not parallel

author: IanB
author_rank: Super Contributor
timestamp: December 02, 2013, 01:43:47 am
content: But the assignment says they have to be connected in parallel. You have to follow the rules of the assignment. You have to do what you are told. Authority must be obeyed!

author: rozeh
author_rank: Regular Contributor
timestamp: December 02, 2013, 06:51:24 am
content: @mariushThanks. It's a good idea. also if I can find these ICes in my country.@GK and @mikeselectricstuffbut the series has a big problem. if one of them will burn then other LEDs will not work.@IanB

author: poorchava
author_rank: Super Contributor
timestamp: December 02, 2013, 06:56:23 am
content: In parallel if one burns, the others get more current and another one burns, and then they all share the current and they are all toast. Unless you driver LEDs way below nominal current so that you have enough headroom in case of failure.

author: rozeh
author_rank: Regular Contributor
timestamp: December 02, 2013, 07:12:16 am
content: @poorchavaReally?

author: IanB
author_rank: Super Contributor
timestamp: December 02, 2013, 07:14:26 am
content: Quote from: rozeh on December 02, 2013, 06:51:24 amIf the LEDs must be run independently, then you first need a circuit to drive a single LED from a 24 V supply, then you duplicate this circuit six times.The circuit to drive a single LED from a 24 V supply will be a suitable current regulating buck driver IC for LEDs.If a 24 V supply is too high to efficiently drive a single LED you might consider first generating a lower voltage rail, say 6 V with a DC/DC step down converter, and then running the LEDs from this.

author: IanB
author_rank: Super Contributor
timestamp: December 02, 2013, 07:15:30 am
content: Quote from: rozeh on December 02, 2013, 07:12:16 amThis will happen if you literally connect the LEDs in parallel and then try to drive them all from a single current source. But you shouldn't do that.

author: rozeh
author_rank: Regular Contributor
timestamp: December 02, 2013, 08:05:26 am
content: Which is the cheapest way, guys? and which is the best for a ship? series or parallel?

author: IanB
author_rank: Super Contributor
timestamp: December 02, 2013, 08:29:15 am
content: Well what are you trying to design?Is it for area lighting, spot lighting or beacons? Interior or exterior? Are the lights to be controlled as a group or individually switchable? Is the design a one-off, or for volume production?It's hard for anyone to say what is "best" without knowledge of what is needed.

author: rozeh
author_rank: Regular Contributor
timestamp: December 02, 2013, 08:42:04 am
content: Quote from: IanB on December 02, 2013, 08:29:15 amfor beacins.exterior.individually switchable.Volume production.

author: IanB
author_rank: Super Contributor
timestamp: December 02, 2013, 09:02:43 am
content: Quote from: rozeh on December 02, 2013, 08:42:04 amJust for clarity, do the six LEDs make one beacon switched on and off as a group, or do the LEDs make six separate beacons that can turn on and off independently?It would be common to put LEDs in series when there are a group of them. But they could also be arranged in two groups of three, or three groups of two.The normal approach would be to use a purpose designed LED driver IC. Pick one that matches the supply voltage, output voltage and LED current requirement. LED lights are so common now that many driver chips exist.

author: rozeh
author_rank: Regular Contributor
timestamp: December 02, 2013, 04:59:48 pm
content: Quote from: IanB on December 02, 2013, 09:02:43 amthe six LEDs make one beacon switched on and off as a group

author: hlavac
author_rank: Frequent Contributor
timestamp: December 05, 2013, 10:34:58 pm
content: I would make a switching buck converter to create a supply rail with voltage about 1V above the forward drop of the LEDs from the 24V input for power efficiency, then give each LED its own current limiting resistor and power all the resistor - LED pairs in parallel from that rail. That ensures reliability when individual LED fail open or change drop voltage drastically.

author: Corporate666
author_rank: Unknown
timestamp: December 06, 2013, 02:47:18 am
content: I would use something like the RT8472 from Ricktek. It is a buck switching LED Driver which can take from 5V to 30V directly and will run up to 1A output current. It also costs $0.25/ea and has a dimming/switching input for easy control of the LED current output.I would run the 6 LED's in series in one string. Failure of one LED is not so much a problem - LED's are diodes and they should not be designed for failure anymore than you would design any other part for failure like any other diode or capacitor or resistor. I always see people wanting to design around possible LED failure - IMO there is no reason for that other than either a bad design originally that is going to fail, or being burdened by the past when bulbs used to burn out (a bad way to do modern designs). After all, we don't design solid state transistors to be replaceable in modern electronics, even though we did with vacuum tubes... same thing.I would heat sink everything REALLY well, then pot the whole thing with clear epoxy and forget about individual component replaceability in favor of reliability/waterproofing.

author: rozeh
author_rank: Regular Contributor
timestamp: December 09, 2013, 07:50:14 am
content: Unfortunately I couldn't find those ICs(you mentioned) in my country. What is your opinion about this circuit?3wat LED constant currentI want to put 3*1wat LED in parallel for each of this circuit. thus, for 6LED I can use of two this circuit for each.

author: rozeh
author_rank: Regular Contributor
timestamp: December 09, 2013, 07:55:25 am
content: like this

author: ttp
author_rank: Regular Contributor
timestamp: December 09, 2013, 10:01:14 am
content: Quote from: rozeh on December 09, 2013, 07:55:25 amThis is just 3.33V voltage supply, no current limiting. In my opinion no good for LEDs.

author: senso
author_rank: Frequent Contributor
timestamp: December 09, 2013, 10:12:57 am
content: Using just a comparator, a couple passives and some transistors you can make a poor mans buck led driver:http://www.instructables.com/id/Poormans-Buck/

author: rozeh
author_rank: Regular Contributor
timestamp: December 09, 2013, 11:13:49 am
content: Thanks ttp and sensoQuote from: ttp on December 09, 2013, 10:01:14 amQuote from: senso on December 09, 2013, 10:12:57 amI don't need to dimming the LEDs. I just want to drive those in parallel.

author: senso
author_rank: Frequent Contributor
timestamp: December 09, 2013, 11:41:01 am
content: Remove the dimming and you get a constant current led driver....

author: IanB
author_rank: Super Contributor
timestamp: December 09, 2013, 02:58:56 pm
content: Quote from: rozeh on December 09, 2013, 11:13:49 amDon't try to drive LEDs in parallel. You will most likely shorten their life and cause them to fail. LEDs must be driven in series, or individually with current balancing. Never in parallel.

author: mariush
author_rank: Super Contributor
timestamp: December 09, 2013, 04:54:58 pm
content: As several people already told you here, driving the leds in parallel is a bad idea. Serial is the way to go, more efficiency.If you're worried that one of the leds will break down and kill all the leds in the chain, then do a compromise and make 2 or 3 sets with 2-3 leds on each set. If one led breaks down, you're going to have lower brightness because only 2 or 3 out of the six leds will stop working.If you're so worried that one of the leds will break down and interrupt the whole chain of leds, why don't you just add some jumpers that will take out the led out of the circuit if it fails?You have 24v, it will be a shame not to just chain the leds and have high efficiency. Just add some jumpers to take leds out of circuit if needed :If you want something stupidly simple, you can use led drivers like these (i used them in the picture above) :http://www.digikey.com/product-detail/en/NSI45090JDT4G/NSI45090JDT4GOSCT-ND/3462437Each of these diode like drivers does up to 160mA (adjustable with a plain resistor) but they can be paralleled to give more current. Since you have 1w leds that means you need about 300 mA so you can simply put two of these in parallel and adjust the current to 150mA each with the resistor and you're done.These led drivers are more expensive but at least they don't need inductors and capacitors and other components so you save money there. Just make sure to read the datasheet and pay attention to thermals (leave enough copper around them so they can stay cool (relatively) )

author: Rufus
author_rank: Super Contributor
timestamp: December 09, 2013, 05:09:40 pm
content: Quote from: mariush on December 09, 2013, 04:54:58 pmMurata make thermistor like anti-fuse devices intended to permanently short out LEDs failing open circuit. Littlefuse make semiconductor parts like two terminal voltage triggered thyristors which are also intended to short out LEDs failing open circuit.