Newbe Q on High Power LEDs Driver

[ajreef]

Hello all, great site and a lot of good reading here! I hope I will make time to go through some of the threads I skimmed over while searching for what I am looking for...

Which by the way is: a proper way to drive and do several things with Seoul's P4 Z-powered leds (~3.5W: 3,5V/1000mA).

**broken link removed**

- I need to drive roughly 3 groups (3 independent panels) of ~70 LEDs in each group.

- There is a need for at least one of the groups/panels to be dimmable (much like I can dim T5 ballast with a 1-10vdc controller)

- If I could source something that would work directly from 220/230VAC it would be great, if not, it doesn't matter.

- The setup of the the LEDs within each group (how many LEDs in series in each strand and how many of those strands in parallel to each other does not matter to me) will be guided from the driver's dimensioning I guess!?

Now, although I know I am in waaaaayyyy over my head, I did take a look at some setups utilizing the following:
Linear Technology's LT3497, National Semiconductor's LM3404HV and finally, Supertex' HV9910.

I do not have enough info to decide on any of them, (and I do not have to, so feel free to propose other setups) so can someone spend some of his/her precious time and help me out a bit in deciding what is the best way to drives these 3 arrays?

 

[ronsimpson]

3 watt LEDs

If you want to get 3.5 watts you need to heat sinks the LEDs.
If you want to get full power from the LEDs you need to monitor their temperature.
This type if LED will not have a long life if you let the temperature get too high.

Dimming is easy.

From the 220AC you can get 300 volts DC. Use a simple buck switching power supply to get the 245 volts needed to drive all 70 LEDs in series. Do not regulate the voltage! Regulate the current!

We produce products that use 1 & 3 watt LEDs.

 

[ajreef]

It is not important for me to get the 3.5W but rather the lumens that manufacturer states at each V/A stage. Valid point on temp, but heatsinking (alum alloys and fans blasting the heat sinks) is not an issue and it has been accounted for.

Ron, you say dimming is easy, can you elaborate???
Also you say with a simple (yet current regulated) buck SMPS I can drive all leds in series at 245+VDC (and I assume 1A) and you also produce such products.

Would you please point me to such products? A link, a pdf, anything would do.

I hope it is as simple as you say it is!

 

[ronsimpson]

Dimming:
I use two different ways of dimming.
1. reduce the current.
2. 100%, 50%, 25%, 12% duty cycle. At 100hz.

I think you will have trouble at 1A. One of our competitors starts out at full current then backs off as the temperature climbs. We start out at the reduced current and have a very simple product.

I use LEDs in flashlights (torches). And toys, night lights etc.
Send me an email if you want more details.

 

[ajreef]

Well I think I didn't make myself clear on what I mean by dimming. I do not care for manually dimming the array.

Rather I want it to build up current slowly but automatically (controlled by a dim controller, that would step up maybe 5-10% till it reaches what I will decide that 100% will be) in a span of, let's say 30 or 45 minutes from the time it first receives power, stay at 100% for 9-11 hours and then start dimming the array down for 30-45 minutes when it is time to completely shut-off the power again.

The manufacturer rates the P4s at 1A maximum, so yes, what I refer too as 100% above will probably be achieved at >800mA and <1000mA (it will depend on the lumens it produces at that current range with 3,7+ volts on it).

Sorry for being a pain, but the question still remains, can someone help with suggesting where to begin to built a suitable PS for such an application with:

Vout -> 37-75VDC
Iout -> 700mA-1000mA (regulated as tightly as possible)
With a dimming interface to accept a 1-10V dim controller?

 

[Sceadwian]

I would recommend well above 100hz for PWM from an LED light source, at least 1khz. LED's are virtually full on/full off devices so their modulation is 'deep' which means you can see flicker easily without a filter. Even at 1khz the modulation depth can let people see harmonic flicker from other light sources or during quick head turns. Granted I am a bit of a freak about this kind of thing because I notice it constantly.

To actually answer your last post, any decent bench power supply will allow 700-1000ma current limiting with a resolution of a few ma's.

Try www.mpja.com, they sell a lot of cheap power supplies and some well regulated benchtop variable current/voltage supplies for reasonable prices. You can likley purchase one from there cheaper and significantly more easiliy than you'd be able to build one.

 

[ajreef]

Sceadwian, thanks for your input.
Hate to sound ignorant, but I actually am when it comes to these issues... so, when you refer to 1KHz PWM (is the pulse wave modulation?) your referencing it for the dimming aspects of things, correct?

I did look at the site you proposed and some other I Googled but I am not sure what I find is what I am looking for. Can you please provide input on the following items? Which one would help me run these arrays properly?

The issue with the dimming as you and ronsimpson are discussing it, is that I need to be able to set a start time in the morning, (ie 8am) and the LED should start dimming upwards to 100% from 8am till 8:45am lets say. Continuous operations from 8:45am till 9pm and then, the opposite at night (ie 9pm) so the arrays should start dimming down at 9pm from 100% to as close to 0% as possible at around 9:45pm.

Can I achieve all (but the dimming part as I described it above) with any of the following bench PS?


http://www.mpja.com/prodinfo.asp?number=14602+PS
**broken link removed**
http://salestores.com/te72troudcpo.html

 

[Gordz]

I found this to be a very interesting way of controlling power to white LEDs.
**broken link removed**

 

[ajreef]

^^^

shameless bump

 

[Diver300]

Dimming:
I use two different ways of dimming.
1. reduce the current.
2. 100%, 50%, 25%, 12% duty cycle. At 100hz.

Why do you use 100Hz?

It is far too slow, especially at small duty cycles where there is most of the 10ms as gap.

**broken link removed**

Those flashing lights are car tail lights that are brakes lights dimmed by reducing the duty cycle.

They are very annoying, and please don't pretend that no-one can see lights flashing at 100 Hz. That may be true for totally static situations, but there is always movement where automotive lighting is concerned.

Lights like that are also illegal in the UK, but it doesn't stop VW, Audi, SAAB, Jag, Merc, Peugeot and others fitting them.

http://www.opsi.gov.uk/si/si1989/Uksi_19891796_en_3.htm#(Tii)i3lampshowsteadylight

 

[ericgibbs]

I found this to be a very interesting way of controlling power to white LEDs.
**broken link removed**

hi Gordz,
Watched the movie, it reminded me of a similar presentation I saw in the 1970's.
The only difference is the use of the White led as opposed to a Tungsten lamp!

Regards