LED DIY : Making of a "DJ SET "-style grow led light .

Ok..Doing some tests ...
Made 3x "loads" ( 3x strings of 10 CW leds in series ....)

Fans work great ...
Massive airflow ..
Rel .low noise ....

I'm having trouble with analog dimming ....

Pot works really great ,with high precision ..
But it does not get any lower than ~550 mA ...

Guod ,any help on that ?
Can't figure out ,what's going wrong....
(180 ohm resistor - 1 K pot )

P2256086.JPGP2256089.JPG.....
 
Yes ,exactly like that ...
I'll change the wires ,because are taken from an old computer...( way thin & flat wiring ... )
Maybe wires too small in Dia ,thus increasing resistance ....
But still ,I do not think that is the reason behind the 550 mA lower limit ....
Can't figure out it ,really ....
Everything is correctly placed ,wired & connected ....
WTF ?

( 180/1180 ) *5 = 0.7627
5 - 0,7627= 4.2372 V ....
Max voltage(with pot ) should have been -as stated - approx .4,2 V ....
~ 112 mA ,had to be , the minimum current limit ....
 
Input voltage you mean ? 48 V ....

As for the rest ,of the voltages ,haven't measure them (yet ) ...
Later on ...
...
I'll post the results ...
I've to go for work ,now ...
 
Input voltage you mean ? 48 V ....
nop, voltages on the pot as given in pic two (Voltage test-points)

next simple test is brigde(red) the contacts you see in this pic, led have to go off
brigde.jpg
 
Yes ,I did that and indeed leds go off ..
bucks work as they should...
please check the smd-resistor with an ohmmeter, looks like this is not 180 ohm but 1800 ohm
 
Nope ...
I still get the same readings ....

P2266091.JPG
Black for GND
Yellow for Vref
Green for Analog Dimming .

P2266095.JPG
Without Pot .
5.43 -5.5 Volt between GND and Vref

P2266096.JPG
Pot :
GND at 1
Vref at 3
(if opposite ,pot operates opposite,as Guod stated .
Just a simple personal preferance issue )....
An.Dim . at 2

P2266098.JPG
Pot fully clockwise : Min current = 550mA (still.... )

P2266099.JPG
Pot at "0" : max current =~ 710 mA .

P2266101.JPG
A. Dim & Ground : 1.14 Volt ,instead of 4.2 ...(with pot )
???

P2266102.JPG
Vref - ground (with Pot ) ..Same ~ 1.14 V ,instead of 4.2 (pot fully turned clockwise ) .....

???

I don't understand ...
WTF is not right ?
 
guod said:
Vref has to be always 5.xx V. should not change if you turn the pot.
Click to expand...
V.ref ( voltage taken with pot on ,between gnd and Vref ...) is not 5.xx
Is ranging from 1.14 (pot at 0 ) to 1.2 (pot at max )

Without pot ,yes, then Vref is ~5.5 Volt .....

Any ideas ,so far ?
 
looks like we have a to high load on Vref. check the resistance between 1 and 3 at the pot. 1000 ohm you should read here.
 
Replaced Vishay 1K pot with one Bourns 3296 high precision-multiturn- trimmer ....
At 10 K .

Went as low as 60mA ...
Really smooth -great! - analog dimming ..
(up to 710mA ... )

P2266106.JPGP2266107.JPGP2266108.JPG


Still don't get it ...
1 k ,is the right one( based on "voltage divider " equations ) , not 10 K ....
 
We need a bigger pot ?

180 & 2200 ?

180/ 2380 =0,0756...*5 = 0,3781
5 -0,781= 4,621
Nope ...~53 mA minimum current ...
"No go " ...
 
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