Question about led drivers
- Thread starter badbreath
- Start date
It depends if the driver can lower its voltage enough to be below max V LED can handle and produce the correct current @ that V. Basically your question cannot be answered without knowing more characteristics of LED and driver. You need to know voltage and current for both. Watts is a product of those two values. So it can be 1V @10A = 10 W or 10V @ 1A = 10W.
badbreath
New member
OK thanks. Can you tell me, Do constant current drivers increase voltage output as more LEDs are added to the circuit?
oreo57
Well-known member
As to my understanding .. yes.. and constant current drivers are never (or rarely) listed as "watts" for this reason..
W=V x A so to take a meanwell driver at 1000mA and a voltage range of
w/ constant current output of 1A..
Meaning it "outputs" 2-52 Watts (or dissipate 52W of heat) ...
in a sense it is self limited.
http://www.meanwell.com/search/LDD-H/LDD-H-spec.pdf
"constant voltage" drivers are different...
badbreath
New member
So then applying this to my op you could say that if my led took 1 amp everything would be fine if it was a 10 watt led or say 5 10 W LEDs connected in series. Correct?
So when shopping one should match led current requirements with driver current outputs and not exceed the max wattage of the driver... Possibly leaving 10% spare wattage to be safe... Ehh?
oreo57
Well-known member
W/ constant current drivers you need to not exceed their voltage needs on the LED side or on the PS side. In series add voltages..10W LED's usually need 9-11v each so 5 in series would need 50 V and they all would run @1 a.with a 1A costant current driver capable of handling 50V.
The power supply would have to output 53V and be capable of handling 50W plus 10%..
As to Watts you need to not exceed your power supply AND it has to have high enough V(out)..
Are you looking at combined ps/drivers or separates?
Example:
Surprise surprise.. 36x3 = 108W.. close enough to their 100W "rating"..
So in the above IF you were using 1W leds w/ a V(f) of 3.6 you could string 10 in series BUT you would have 3000mA going through them...
Add a parallel branch of equal number and you "split" the amps in 2. Each string now sees 1500mA..
double that and you now have 10x 4 array w/ each "branch" getting 750mA.. finally reasonable considring the usual " amp Rating" of the LEDs..
Problem comes when 1 " fails" open.. that means all 3000mA is going into 3 branches.. (1000mA each) . If one more fails open, most likely you will burn out all of them..(1500mA into 2 strings)
See not really much about Watts..
W/ separates.. matching voltages really comes first.. If your constant current driver is rated at 2-36V you don't hook it to a 50V ps. If your LEDs need 50V you don't hook it to a driver that only outputs 36V max..
Then you can decide what current you want to run your LED's at..and to make sure your PS can supply it..
sometimes ps and driver are one.. sometimes not..
Last edited:
badbreath
New member
Thanks for the info. I think I'd be looking at combined power supply/driver.
Are high power LEDs (30-100 watt) usually powered by individually by the drivers or are they commonly connected in series to a single driver? Seems like it is the 3 W LEDs that are wired in series to a single driver.
oreo57
Well-known member
Depends.. Usually , to save cost and add simplicity and increase coverage.. as many as the PS can handle..
multichips (high W) are just small LEDS in series/parallel rows inside.
Like 10W LEDS internally are 3 columns of 3 in series..
Length of rows determines V(f). Number of rows determines mA draw..
I suppose quality/similarity could affect them in series more so than having each on it's own driver..
Considering you'd need like a 72V DC out for 2 100W chips it is a prohibitive to have 2 or more..
2 in parallel and you get a 6A out driver .. If one fails it will toast the other as all 6a is shunted into the remaining one..not to even mention problems w/ "matching"
I think you'd have to be a masochist to run high W chips in parallel. you can protect them from that w/ fuses ect.. and you can match currents so they aren't different looking but all that is a lot of extra circuitry.
Last edited:
badbreath
New member
Depends.. Usually , to save cost and add simplicity and increase coverage.. as many as the PS can handle..
multichips (high W) are just small LEDS in series/parallel rows inside.
Like 10W LEDS internally are 3 columns of 3 in series..
Length of rows determines V(f). Number of rows determines mA draw..
I suppose quality/similarity could affect them in series more so than having each on it's own driver..
Considering you'd need like a 72V DC out for 2 100W chips it is a prohibitive to have 2 or more..
2 in parallel and you get a 6A out driver .. If one fails it will toast the other as all 6a is shunted into the remaining one..not to even mention problems w/ "matching"
I think you'd have to be a masochist to run high W chips in parallel. you can protect them from that w/ fuses ect.. and you can match currents so they aren't different looking but all that is a lot of extra circuitry.
Awesome! Thanks for the information.
Also you have to take into account if you want to make a controllable fixture. Making simple on/off fixture similar to MH out of multichips is fairly easy. Making controllable colors with programming, etc. is a little bit harder, since you need drivers for each channel/color and computer to control each. Hence the cost of Radion, etc.
