tams elektronik
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LC modules
Serial connection of LEDs
With a serial connection all LEDs have to be connected (in series) via
one series resistor to the output. The current consumption of the LEDs
depends on the value of the series resistor. The higher the value, the
lower is the current. But, the LEDs are dimmer, the higher you choose
the series resistor´s value.
The number of LEDs you can connect in series depends on the transformer
´s nominal voltage and the colour of the LEDs. When connecting too many
LEDs, the voltage is not sufficient and the LEDs do not light.
Examples for serial connection of LEDs:
Nominal voltage
transformer (~)*
1
Operating
voltage *
1
appr.
Forward voltage
of the LED*
2
Max. number of
LEDs*
3
per output
12 V
17 V
2 V
7
4 V
3
16 V
22 V
2 V
10
4 V
4
18 V
25 V
2 V
11
4 V
5
*
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
V
[Ohm] = ( U
B
[V] – U
F
[V] x n
LED
) / (I
F
[mA] x 0,001)
U
B
= operating voltage| U
F
= forward voltage of the LED
n
LED
= number of LEDs | I
F
= current with max. luminance
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