LED MeanWell power supply?

[evilc66]

Current mirrors are transistor based that controls the current acurately between two parallel strings. The method that Meanwell uses is simple, but doesn't save you from total disaster. Plus it adds a ton of wiring. A current mirror is placed at the end of the strings.

 

The ELN-60-48 can be turned down to just under 1000mA.

[npain316]

Dag Nabbit Evil, now you've got me worried!

So I've swapped one of these( ELN-60-27,non-dimmable) for a for the buckpucks. Two // strings of 8 LEDs (a mix of blues and whites to a color temp of my taste). I realize no dimming - but its not important.

 

I'll have to recheck my numbers tonight, but I'm at ~28V and ~800mA per strand. So far, this puppy is working great! but what about, as someone alluded to above, when an LED goes out down the road? What do I need to "protect" myself?

 

Thanks,

Nick

[evilc66]

I have been doing more reading into it, and current mirrors can be made really easily with two transistors.

 

 

Article here.

 

Interesting article. The last section really describes how the current mirror protects things.

[npain316]

I have been doing more reading into it, and current mirrors can be made really easily with two transistors.

 

 

Article here.

 

Interesting article. The last section really describes how the current mirror protects things.

1st: an led magazine!!! Sweet!

2nd: sweet article, I can't believe the variation that can form across two strings. A must read for all!!! Thanks fors sharing.

3rd: This does seem very simple. Can I get these tranistors and resistors at RS, any suggestions for protecting these from the "elements" of SW?

 

Thanks, Nick

[evilc66]

You should be able to get similar transistors at RS, but you won't find the right resistor values. Might as well get it all online.

[npain316]

You should be able to get similar transistors at RS, but you won't find the right resistor values. Might as well get it all online.

When it says the two transistors need to be thermally connected, could this be as simple as them mounted to the same piece of aluminum (scrap piece) with some AS5? or do they need need something with more mass, like a heatsink?

 

I guess what I'm asking is will these things generate a lot of heat?

 

Thanks, Nick

[evilc66]

They could generate heat, but it's more to make sure they drift at the same rate because of temperature changes.

[The Propagator]

evil you make my head hurt brother !!!

 

How the hell do you retain all of that ?

[evilc66]

Thats a good question

[Ocean Flyer]

Thank evilc66.

I will try out and see which one work.

 

Cheers

 

Hi Sherman,

 

any finding ?

 

Await for result !

[amnesiak]

Hey all,

saw this thread from another one (evil referenced this one).

1. Did anyone actually get their hands on a dimmable version of the power supply? There's a much cheaper solution that would probably work, and

2. You should be able to use that PWM circuit evil posted on your existing non-dimmable power supplies. Just connect the source of the transistor (the part with the arrow) to ground and make sure your LEDs are above that. You have to make sure the FET (transistor) you're using can handle the current and it's a 'logic level' FET. From a cursory glance the schematic evil posted looked good but if anyone wants to try it i'll look at it closer. Worst thing that happens is that you let the magic smoke out.

3. When you're building current mirrors, for the two matched transistors, use ones that are packaged together. Here is a quad-packaged set of BJTs (another type of transistor, different from a FET) that you can use for current mirrors. In addition to being thermally coupled, you can be sure that you'll have the same process characteristics -> good mirroring. However, you'd probably have to look a while to find a set of BJTs that would support 1A for the LEDs folks are using on this forum.

 

edit: that quad pack of BJTs would work fine for a 350mA current mirror as above

edit2: I now see there's a dc-dimmable version and a pwm dimmable version, #1 should work for the dc-dimmable versions

[amnesiak]

I have been running the non-dimming versions with out issue for a couple months, so I was working with the Arduino and decided to order two dimming versions. They arrived today, and I was hooking it up to the Arduino using the PWM function, I know it only drives at 5 volts, but just to play with dimming. It worked to 50% dimming (100% duty at 5v.) I was measuring the current, and the lights would fire up at .25 amps (.125 amps per string) and ramp up to .66 amps. Evil do you have a circuit on allowing the Arduino to drive to 10v still using PWM from the Arduino, or any other thoughts on getting this to work fully? Thanks.

 

zingtaw,

I'm new to this thread (and to the site too). I have something simple you can try:

If you're using the 48V version, connect a 36K resistor to the +48V output. Connect a 10k resistor to the 36k resistor and then to ground. Get a cheap BJT (transistor, 2n222 works), connect the collector to the 10k/36k node, the emitter to ground, and your arduino output to the base. The DIM+ is connected to the 10k/36k/collector node and dim- to ground. You also have to make sure your arduino is connected to your PS ground.

 

The 36k/10k resistor combo is a 'resistor divider' and creates a ~+10V reference that only draws 1mA of current. The transistor switches that node between the 10v reference and ground.

 

This and other resistor divider solutions (like a 36k resistor in series with a 10k pot) that don't use a separate 10v power supply are based on a couple of facts I'm guessing on that are missing from the power supply datasheet:

1. When the current is set to 0 by dim+/-, it's not really 0 (leakage from the power supply)

2. Dim+ is a hi-z input (1Mohm+) and doesn't require much current to work.

 

#2 I'm pretty sure about but #1 needs some experiments.

[evilc66]

I would be careful suggesting pwm'ing the output on a buck driver. If it is not designed correctly (the driver) the pwm could cause damage with a virtual switch to ground. Many times when a buck driver uses a pwm external switch, it's before the inductor, not after.

[amnesiak]

I would be careful suggesting pwm'ing the output on a buck driver. If it is not designed correctly (the driver) the pwm could cause damage with a virtual switch to ground. Many times when a buck driver uses a pwm external switch, it's before the inductor, not after.

 

I think you're right on that... I'll ask someone that knows a bit more about power supplies than I do (I'm a digital design/electromagnetics guy). Are you sure the meanwells are buck converters? They might just be choppers.

 

Also, if you have one of the DC-controllable supplies can you test the resistor divider circuit out when you have time? 36k-10kpot-1k (to keep the min voltage to 1v, give the pot more range). I'm curious to see if there's enough leakage to make it work correctly.

[evilc66]

I'm pretty sure they are bucks. I do have one, and I have been meaning to get around to play with it, but time hasn't been on my side

[Sherman]

Today I try to power the LED rung(6 in series) using the Meanwell ELN-60-24-P after getting a PWM for motor speed control

[Sherman]

Light up the rung .

 

Was able to dim the LED rung but the dimming range was very small.

Less than 5 degree of the potientiometer range.

[evilc66]

Details on the PWM unit?

[Sherman]

This is the Circuit of the PWM

[evilc66]

Bigger please?

 

Also, what voltage are you supplying this?

[Sherman]

I use 9 VDC first then after that I use 12 vdc

[evilc66]

I would suggest building the circuit I posted earlier, just due to the fact that you know what the output frequency is based on the resistor values. It's possible that the circuit you used may be out of the usable frequency range.

[Sherman]

It say the usable frequency is 3.6kHz

[evilc66]

Well, thats a potential problem. Max input frequency on the driver is 3khz.

[Sherman]

So that is the culprit. What can I do to change the frequency?

Or maybe it easier to build one myself