I have "inherited" a LED Array that is used as a grow light in a hot house
environment. The problem is that the power supply that comes with the array
has gone missing and the LED array has no markings so I am unsure what
brand it is. I have pulled apart the LED array and it consists of 15
parallel "strings" of LEDs. Each string consists of 15 LEDS (of which 11
are red and 4 are blue) and each string is terminated by a 47 ohm resistor.
Any suggestions as to what the power supply might be?
I am thinking that the current through each LED should be about 15mA so for
a single string of LEDs:
1.   the voltage drop across each red LED is about 1.8V so for 11 red LEDS
the voltage drop would be 11 x 1.8 =3D 19.8V
2.  the voltage drop across each blue LED is about 3.5V so for 4 blue LEDs
the voltage drop would be 4 x 3.5 =3D  14V
3.  the voltage drop across the 47 ohm resistor =3D 47 x 15mA =3D 0.7V
so the power supply voltage should be 19.8 + 14 + 0.7 =3D 34.5V and with 15
strings of LEDs the current should be 15 x 15mA =3D 240mA.
Does this sound about right or am I missing something??
--=20
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