Looking for a specific DC CC driver for LEDs

oreo57 said:
But can it output 3.5A constant current..?

Besides:


you didn't read it very well..
And they're $5 each...
http://www.linear.com/purchase/LT3955
Click to expand...


I can - it can be used in this mode, but I'd take a look at the reference designs. It's going to require an external PWM low side switch and over current protection circuitry. Your raw BOM cost is much higher.

Raw cost of the A6211 is <$1: http://www.digikey.com/product-detail/en/A6211GLJTR-T/620-1477-1-ND/3597453. A shunt is still required, but you can drop a number of external parts.
 
http://www.linear.com/product/LT3791
different variation on the theme...
;)

The IC "is" the driver..
Look, to be honest, I'm only throwing out what "looks" to be quite possible for you. Others better at this "stuff" needs to follow up..
The LT®3791 is a synchronous 4-switch buck-boost LED driver controller. The controller can regulate LED current up to 52V of LED string with input voltages above, below, or equal to the output voltage.
Click to expand...
 
And the Allegro can do 3.5A??
Don't care how cheap it is if it can't do the job..or if I have to drop $3 worth of copper onto it (just in general terms. not my $'s)
You stated above "possible".. How possible to run at 3.5A


this stuff is all above my pay grade.. but if saving $4 is what is at stake here, and by running a chip off spec.. well have at it.

To help the op poster out, say you use the LT chip, what is an est cost per assembled driver?

And My first question was could one regulate 3.5A wasn't answered either..
I'm doing my own lern-in.

I'm not asking for a semester of basic electronics here..

BTW I am well aware that things usually are not "simple" but no need to make it purposely obtuse..

from a naive standpoint, I can't see a driver built around that chip (3955, like you said the other one has external MOSFETS) costing much more than the requested $10.. Well let's go to $15.
and a drive built around the Allegro? w/ heatsink.. $5

Lets stick w/ the 3955.. Looks easier (and cheaper) to design around.
 
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oreo57 said:
And the Allegro can do 3.5A??
Don't care how cheap it is if it can't do the job..or if I have to drop $3 worth of copper onto it (just in general terms. not my $'s)
You stated above "possible".. How possible to run at 3.5A


this stuff is all above my pay grade.. but if saving $4 is what is at stake here, and by running a chip off spec.. well have at it.

To help the op poster out, say you use the LT chip, what is an est cost per assembled driver?

And My first question was could one regulate 3.5A wasn't answered either..
I'm doing my own lern-in.

I'm not asking for a semester of basic electronics here..

BTW I am well aware that things usually are not "simple" but no need to make it purposely obtuse..
Click to expand...


It's possible, assuming several things:

- Low thermal resistance on the board. This is hard to predict without seeing the design.
- Frequency chosen (lower will reduce switching losses, but also require a larger inductor)
- Ambient temperature remains low enough.
- switching ratio. The requested regulation ratio is ideal here for maximum efficiency.

FWIW I would not casually recommend pushing the driver in the design unless you are familiar with the basics of designing buck regulators. It *can* be done and enough information is available in the data sheet to calculate it out from the looks of it.

Another consideration for the OP: what is the true maximum current your LED can take? The output of a buck converter has non trivial levels of ripple current which may exceed your stated current limit. This is something that can be controlled via an output capacitor with trade offs.

As for cost, all in including (small qty) PCB my LM3414 8-up design runs about $5 a channel, with up to 1A drive per channel.
 
Thanks.. but then again he wants 3.5A/channel....

As to the o/p a "out of the box, solder it to the ps 3.5A cc driver" is pretty much a no go.. AFAWeCT...???

which leaves building one based on any number of chips..
 
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oreo57 said:
Thanks.. but then again he wants 3.5A/channel....

As to the o/p a "out of the box, solder it to the ps 3.5A cc driver" is pretty much a no go.. AFAWeCT...???

which leaves building one based on any number of chips..
Click to expand...


I don't know of one that fits all the requirements out of the box. :)

If karimswreef is interested, I'd be willing to do a PCB design for one of these ideas. Time till you get them in your hands will be much longer, but would be a fun project none the less.

Let me know some details of form factor, etc
 
Not using an IC driver controller is a function of laziness and time ... I love DIY, but I don't want to do layout for 20 driver circuits, even on a single circuit board.

The distinction I make is between a driver (complete solution DC-DC), driver IC (just the semiconductor, still needs FETs and Inductors), driver IC controller (also needs PWM and other components).

My preference would be a complete solution for $10.

The LED can take 3.5A max at 34V (120W). I'm running at 100W (3A) for margin. The buck (or boost) output ripple is a function of the output capacitance, but I'd rather not design the circuit.

The Sure driver looks closest so far
http://store3.sure-electronics.com/ps-sp12153

I just need a real datasheet to confirm it can run 3A at 34V. Some thermal curves to show if it's going to need a lot of cooling would be great too.
 
karimwassef said:
Not using an IC driver controller is a function of laziness and time ... I love DIY, but I don't want to do layout for 20 driver circuits, even on a single circuit board.

The distinction I make is between a driver (complete solution DC-DC), driver IC (just the semiconductor, still needs FETs and Inductors), driver IC controller (also needs PWM and other components).

My preference would be a complete solution for $10.

The LED can take 3.5A max at 34V (120W). I'm running at 100W (3A) for margin. The buck (or boost) output ripple is a function of the output capacitance, but I'd rather not design the circuit.

The Sure driver looks closest so far
http://store3.sure-electronics.com/ps-sp12153

I just need a real datasheet to confirm it can run 3A at 34V. Some thermal curves to show if it's going to need a lot of cooling would be great too.
Click to expand...


Zooming in on the board, the main controller is "SYHB" which is the shortcode for an LM3409

http://www.ti.com/lit/ds/symlink/lm3409hv.pdf

It uses an external PFET for the buck driver. I can't find anything on the main PFET (Q1).

The limits on the board would be Q1, L1 (the inductor max DC current), and the sense resistor, which looks like its made up of a bunch of selectable 0603 parts and may not be adequate. You'll probably need to replace some of these to get to 3.5A.
 
theatrus said:
I don't know of one that fits all the requirements out of the box. :)

If karimswreef is interested, I'd be willing to do a PCB design for one of these ideas. Time till you get them in your hands will be much longer, but would be a fun project none the less.

Let me know some details of form factor, etc
Click to expand...

Thanks, man. I think it's a lot of work - but if you're volunteering to help :)

I'm not in a rush, but we'd need to find a way to test it without risking the LEDs - they're a little pricey... $160 each for the high end. That's why I'm trying to save every penny - so I can afford the better LEDs.

I guess I could use the ultra-cheap equivalents to prove the system in.
 
theatrus said:
Zooming in on the board, the main controller is "SYHB" which is the shortcode for an LM3409

It uses an external PFET for the buck driver. I can't find anything on the main PFET (Q1).

The limits on the board would be Q1, L1 (the inductor max DC current), and the sense resistor, which looks like its made up of a bunch of selectable 0603 parts and may not be adequate. You'll probably need to replace some of these to get to 3.5A.
Click to expand...

Yep says that right below..
Note: * from Data Sheet of LM3409 chip. Please refer to the relevant documents for the details
Click to expand...

sorry.. I'm done here.. To the o/p your turning down a GREAT deal from him to get exactly what you want..

And yes to squeeze 3500mA out of that the inductor is wrong..
More like this one my guess, to go up to 3500mA..
http://uk.farnell.com/bourns/srr1260a-180m/inductor-power-18uh-3-9a-20/dp/2374125RL

but why mess w/ it.. 3000mA is OK..
 
karimwassef said:
Thanks, man. I think it's a lot of work - but if you're volunteering to help :)

I'm not in a rush, but we'd need to find a way to test it without risking the LEDs - they're a little pricey... $160 each for the high end. That's why I'm trying to save every penny - so I can afford the better LEDs.

I guess I could use the ultra-cheap equivalents to prove the system in.
Click to expand...

It would be an interesting project none the less - can't quote on a timeline just yet.

The SureElectronics find is not a bad deal at all FWIW - doesn't meet all the specs but would be a way to bootstrap your project.
 
So... no ready made solution??

Why doesn't meanwell make the an LDD at 3.5A 34V... an LDD-3500H ... that's what I really want. :(
 
hard to believe there's no product that does this already.

How about a buck only version 48in 34out? Or a boost only 24in 34out?

I can change the DC input from 12V to 48V in steps of 12, does that help? All I need is to convert my constant voltage power to constant current with a small modulation from 36VDC input to 34VDC output and dimming.
 
karimwassef said:
How about putting 3 LDD-1000H in parallel each with a resistor/diode

http://www.mouser.com/ProductDetail...=sGAEpiMZZMt5PRBMPTWcaTWeSxpmncu0L/IWPcfVhi4=

That's $18, but it's better than $50.

I found this example of someone making it work:
http://www.nano-reef.com/topic/330355-ldd-driving-more-then-1000ma/
Click to expand...

The last quote sums up the risk:

IMPORTANT NOTE - Normally when attaching buck converters in parallel you slave the switching clocks to avoid inducing low frequency ripple on the output. This is caused by minor differences in the switching frequencies, on the order of a few Hertz. I don't know what kind of filtering these devices have but it is STRONGLY RECOMMENDED that you DO NOT EXCEED 80% max capacity. This should provide enough wiggle room that if the converters start "beating" it will not blow out your LEDs.
Click to expand...

The switchers are not synchronized (there is no way to sync multiple LDDs), and load sharing will not be split very evenly, but it is possible to run in this configuration. Its also likely an EMI mess but thats a given for most of the long cable run LED builds here :spin2:

Also the output resistor is just for a model and need not be included. Depending on the LDD construction the diode may also be optional (haven't really looked). I'd suggest a 2A+ Schottky diode for each LDD, rated for at least 50V.
 
karimwassef said:
How about putting 3 LDD-1000H in parallel each with a resistor/diode

http://www.mouser.com/ProductDetail...=sGAEpiMZZMt5PRBMPTWcaTWeSxpmncu0L/IWPcfVhi4=

That's $18, but it's better than $50.

I found this example of someone making it work:
http://www.nano-reef.com/topic/330355-ldd-driving-more-then-1000ma/
Click to expand...
STRONGLY RECOMMENDED that you DO NOT EXCEED 80% max capacity. This should provide enough wiggle room that if the converters start "beating" it will not blow out your LEDs.
Click to expand...

your bulbs..but if is anything like (and it probably is) paralleling power supplies.. the risks seem to outweigh the rewards.. Besides as shown, "proper" drivers can be built.. for fairly cheap..and relatively simple.
 
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