DIY multichip LED - driver question

[Kairus]

I've been doing some testing w/ multichips, I ordered 2 cool white 30w chips, and 2 460nm 50w chips. The 50w chips should be here by the end of the week, but I've had time to play around with the 30w LEDs. They're pretty bright even without a lens and reflector.

They came with some super cheap Chinese no-name drivers, and I wired it up and it worked fine for a while, but now one of them seems to have died. Board looks fine, but I tested with a multimeter and no output (tested input it's fine). The other driver is still chuggin' but I doubt it will last too long.

The chips are 33-35v @ 1a and I've been having a difficult time finding a suitable Meanwell driver. Not many places seem to carry the 36v variations, and some places want $100+ for them (***).

I was wondering if this would work:

It's a buck step-down converter that has adjustable voltage and current, and does up to 8a.

Input Voltage: DC 7-40V
Output voltage: DC 1.25-36

I would just get a 36v DC power supply, figure 2v drop I'd still have room for adjustment, and I could adjust the current down to 1a (or lower, that'd be good for dimming).

Any problems with that? I assume it's essentially the same thing premade drivers do, and I see buckpucks were/are pretty popular, and this is the same concept, just adjustable correct?

Can I just use a printer power supply? I've found a bunch of 36V DC ones, around 1.8-2a.

 

[mcgyvr]

meanwell LPF-40D-42 ($30 each)
rated .96A at 25.2 min to 42v max
and get a 100k ohm potentiometer for "dimming"

 

[oreo57]

I've been doing some testing w/ multichips, I ordered 2 cool white 30w chips, and 2 460nm 50w chips. The 50w chips should be here by the end of the week, but I've had time to play around with the 30w LEDs. They're pretty bright even without a lens and reflector.

They came with some super cheap Chinese no-name drivers, and I wired it up and it worked fine for a while, but now one of them seems to have died. Board looks fine, but I tested with a multimeter and no output (tested input it's fine). The other driver is still chuggin' but I doubt it will last too long.

The chips are 33-35v @ 1a and I've been having a difficult time finding a suitable Meanwell driver. Not many places seem to carry the 36v variations, and some places want $100+ for them (***).

I was wondering if this would work:

It's a buck step-down converter that has adjustable voltage and current, and does up to 8a.

Input Voltage: DC 7-40V
Output voltage: DC 1.25-36

I would just get a 36v DC power supply, figure 2v drop I'd still have room for adjustment, and I could adjust the current down to 1a (or lower, that'd be good for dimming).

Any problems with that? I assume it's essentially the same thing premade drivers do, and I see buckpucks were/are pretty popular, and this is the same concept, just adjustable correct?

Can I just use a printer power supply? I've found a bunch of 36V DC ones, around 1.8-2a.

Meanwell Ldd-1000h (or HW if you like wires)... you have the power supply..
If you plan on dimming..
Personally I'd go w/ 700mA drivers if you aren't planning on dimming..

 

[Kairus]

Meanwell Ldd-1000h (or HW if you like wires)... you have the power supply..
If you plan on dimming..
Personally I'd go w/ 700mA drivers if you aren't planning on dimming..

So with the LDD series your output voltage is based on your input voltage minus V drop? I'm not sure how they would be a better option than a step down that I can control both voltage and current with. I could at least dim them by dropping the current with that chip.

 

[oreo57]

So with the LDD series your output voltage is based on your input voltage minus V drop? I'm not sure how they would be a better option than a step down that I can control both voltage and current with. I could at least dim them by dropping the current with that chip.

You would control current via PWM.. there is no need to control voltage w/ LED's... ever really..unless you were running constant voltage LEDs (not recommended)

Meanwells step up the V automatically till max mA draw.. The Ldd's are identical to what you have minus v control.. again this is unnecessary..

IF you are really concerned there are threads here discussing Meanwells w/ both V and A control (I have some of those as well).. most say "why" to V control

A 4 channel Typhon for PWM control is like $50

Why they are a better option is 1)Seem more robust than what you have 2) cheap ($7/each or so 3) PWM dimmable 4)pretty standard build module here ..

If the led was a voltage controlled device it would be brigher with 24v @ 20ma then with 9v @ 20ma.

as long as the forward voltage is satisfied, it is a current controlled device. You change the current to control the brightness.

you should also remember that when a LED is connected to higher voltage above 1.7v, even 30v with a very low current source( such that the current delivered by the source is very less than the maximum current limit of LED )nothing will harm the LED.

http://forum.allaboutcircuits.com/showthread.php?t=39855

 

[Kairus]

You would control current via PWM.. there is no need to control voltage w/ LED's... ever really..unless you were running constant voltage LEDs (not recommended)

Meanwells step up the V automatically till max mA draw.. The Ldd's are identical to what you have minus v control.. again this is unnecessary..

IF you are really concerned there are threads here discussing Meanwells w/ both V and A control (I have some of those as well).. most say "why" to V control

A 4 channel Typhon for PWM control is like $50

Why they are a better option is 1)Seem more robust than what you have 2) cheap ($7/each or so 3) PWM dimmable 4)pretty standard build module here ..



http://forum.allaboutcircuits.com/showthread.php?t=39855

I'm not looking to control voltage if I don't have to. I guess I don't have a great understanding of how voltage works in this situation and being able to set the voltage and the current seems like an easy solution.

So LEDs will take whatever voltage is given to them right? Too much voltage they die, too little they won't start.

So say we're taking about these LDD-H drivers, what determines their output voltage since they're capable of outputting 2V-52V? Would it be determined based on the input voltage?

 

[oreo57]

too little they won't start.

Yes

So LEDs will take whatever voltage is given to them right? Too much voltage they die,

IF the current is enough. Yes if you force the potential high enough to basically blow the circuit. This is why you have drivers..

You can overCURRENT an LED. Voltage on the LED is fixed by Vf - the voltage drop across the device when conducting in the forward direction (which is its normal operating regime), which is fixed over a wide range of currents.

http://www.candlepowerforums.com/vb/showthread.php?177581-overvolting-led-s

So say we're taking about these LDD-H drivers, what determines their output voltage since they're capable of outputting 2V-52V? Would it be determined based on the input voltage?

Magic.. er just kidding.. They don't care ..
Hook a 36V power supply to 1000mA Ldds .. run any combination of voltages up to ps max (minus 4v approx)..
3V w/ 1 LED 10 @3V= 30V Leds doesn't matter one bit..

As long as they can take 1000mA... voltage is self regulating so to speak...

LED's are written like this 1000mA @ 3V . String 10 together and the potential will be at 30V @ 1000mA.. Driver is happy to supply 1000ma and will output 30V.. You string 5 together it will output 15v @1000mA ect..
It is that simple..

Your overthinking this..
your real restriction is wattage...

Anyways:
http://www.meanwell.com/search/LDD-H/LDD-H-spec.pdf

 

[oreo57]

Found a better way to state it:

Current is approximately an exponential function of voltage according to the Shockley diode equation, so a small voltage change may result in a large change in current. If the voltage is below the threshold or on-voltage no current will flow and the result is an unlit LED. If the voltage is too high the current will go above the maximum rating, heating and potentially destroying the LED.

It is therefore important that the power source gives the right current. LEDs should only be connected to constant-current sources. Series resistors are a simple way to passively stabilize the LED current. An active constant current regulator is commonly used for high power LEDs, stabilizing light output over a wide range of input voltages which could increase the useful life of batteries. Low drop-out (LDO) constant current regulators also allow the total LED voltage to be a higher fraction of the power supply voltage. Switched-mode power supplies are used in some LED flashlights.

http://en.wikipedia.org/wiki/LED_circuit

 

[mcgyvr]

You don't control the voltage and control the current with that device pictured above..
You put it into constant voltage (and can adjust voltage) or into constant current mode (and can adjust current)..

LDD is very similar but its set to constant current mode only and has a fixed output current (that can be adjusted electronically via a 5V pwm signal). The pictured device required you to manually turn the potentiometer to adjust output current and can easily be over-turned to destroy the LEDs.. and its Chinese junk..haven't you already learned with the blown drivers that you already got.

Both the LDD and that pictured device also require a constant voltage AC to DC power supply with a voltage output at least 2V greater than the max Vf (forward voltage) of your LED..

A meanwell LPF and similar like I said in post #2 is like getting an LDD and the ac/dc power supply in one nice plastic box.