And just out of personal curiosity ,I've tried to "decypher" the internal connection of Vero 29 (ver. 1.2 ) Array 's dies .
The known values :
Vero 29 :
Number of dies : 156
Nominal If : 2100 mA (Tc=25°C )
Maximum If : 4200 mA (Tc=25°C )
Nominal typical Vf : 38.0 (Tc=25°C )
Maximum typical Vf : 40.4 (Tc=25°C )
Bridgelux dies ( BXCD4040 -BXCD4545 -BXFE4545 ) :
Nominal If : 350 mA (Tc=25°C )
Maximum If : 700 mA (Tc=25°C )
Nominal typical Vf : 3.4 (Tc=25°C )
Since the max If of Vero 29 is 4200mA and the max If of dies is 700mA ,then :
4200 / 700 =
6
So,most probably inside the Vero 29 ,under the LES there are :
156 / 6 = 26
6x strings of leds ,connected in parallel ,each string having 26 LED dies ,right ?
No !
And that is because 26 x 3.4 = 88,4 V
The typical Vf of Vero 29 at 2100 mA is 38 V .
So let us try 38 / 13 ...(26/2 ) = 2.92 V ..
Then ,Vero 29 has most probably 12x strings ,parallel connected ,each string having 13 dies .
(12 *13 =156 )
But then ... 2100 / 12 = 175 mA (half of 350 mA )
At 175 mA ,almost every Bridgelux die has a Vf about 2.92 V !
-Check the Vf vs If logarithmic scaled graphs of the dies spec-sheet-
That means -most probably- that indeed under the LES of a Vero 29,
there are 12x strings parallel connected, of 13 dies per string .
At the max If of Vero 29 ( 4200 mA ) ,each die has an If of 4200/12 =350 mA
Which means that a Vero 29 can be driven up to
8400 mA,
in order for the dies to reach their If max of 700 mA .
Still ,this is not the case ,due to efficiency drop and the cooling issues .
So ,when a Vero 29 is driven at
2100 mA ,every each one of it's 156 dies ,
has an If of 175 mA.
(The radiometric efficiency of each die is well above 50% ,@ 175 mA )
Thus the increased overall efficiency of the COB array,since the dies are driven at half of their nominal If .
(
When a Vero 29 is driven at 350 mA ,then each die has an If of 350/12= 29,166 mA .
An If similar of the classic small epoxy signal leds ( If=20 mA ).
But with more than 2000 times less thermal resistance than of a typical 5mm epoxy encapsulated signal LED.
( Less than 0.13 °C/W as opposed to 300°C/W )
Let alone the actual output -compared - at ~30 mA ...
Try to duplicate that ,using 1 Watt LEDs driven at ~30 mA ...
The space & volume neened is going to be many times more ...
Let alone the MCPCB/ IMF and it's restrictions ... )
Chip-On -Board LEDs ..
What a wonderful invention ,indeed !
Cheers.