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LC modules
Examples for serial connection of LEDs:
Nominal voltage
transformer (~)*
12 V
16 V
18 V
*
1
Nominal voltage and operating voltage: The operating voltage with a.c. transformers is
approx. 1,4 times the nominal voltage given on the transformer. With d.c. power packs the
operating voltage corresponds to the given nominal voltage.
*2
The forward voltage of white and blue LEDs is approx. 4 V, differing coloured LEDs approx. 2 V.
*
3
Tolerance and / or voltage fluctuations in practice often cause the calculated operating
voltage not being available. For that reason it is recommended to connect one LED less than
possible in theory.
Calculate the necessary series resistor as follows:
nec. R
[Ohm] = ( U
V
U
= operating voltage| U
B
n
= number of LEDs | I
LED
Example: Connection of 2 blue and 3 red LEDs with using a 18 V a.c.
transformer. Designated current: 20 mA:
nec. R
= (25 V – 4 V x 2 – 2 V x 3) / (20 mA x 0,001) = 550 Ohm
V
We choose the next resistor´s value which is provided as a standard,
which means a resistor of 560 Ohm. If using a resistor with a higher
value the current of the LEDs would be reduced and the LEDs would
light less brightly.
Operating
1
voltage *
1
appr.
17 V
22 V
25 V
[V] – U
B
F
= forward voltage of the LED
F
= current with max. luminance
F
Forward voltage
of the LED*
2 V
4 V
2 V
4 V
2 V
4 V
[V] x n
) / (I
LED
Max. number of
2
LEDs*
3
per output
7
3
10
4
11
5
[mA] x 0,001)
F
English
Page 27
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