OSRAM OPTOTRONIC Constant current LED power supplies with 3DIM - Manual (Page 14)

14
Vset Rset Iset
LEDset APPLICATIONS
Note 1: The E96 series covers a wide range of values. The
table contains only some sample values of this series. Please
check the standard E96 series to fi nd the value best suited
for meeting your current setting requirements.
Note 2: The values given above are calculated without con-
sidering the possible power and/or output voltage and/or
minimum output current limitations which depend specifi cally
on the output characteristics of the chosen ECG. Please
refer to the respective product datasheet.
Note 3: The resistor tolerance has an effect on the accuracy
of the current setting. Available standard tolerances are 5 %,
2 %, 1 %, 0.5 %, 0.25 % and 0.1 %. LEDset ECGs are de-
signed to provide up to 5 % of the overall control accuracy
(Rset – Iout) if Rset is a resistor with a tolerance of up to 1 %.
If higher than 1 %, the tolerance of Rset must be considered in
the Iout tolerance calculation.
Example:
This example is meant to help in choosing the most suitable commercial resistor for a given system.
The calculation applies to an OT 35/220-240/700 LTCS in LEDset confi guration to set an output current of 580 mA.
Starting from the basic relationship:
Therefore:
Looking at available values of commercial resistors (i.e. E96 series), 30.9 kΩ is the best choice.
The recalculated real current setting would be:
Note 4: Since the Iset current value is very low, the power
rating of the resistor is not an issue to be considered when
selecting the resistor (considering a maximum value of
50 kΩ PRset = 3.8 mW).
Note 5: If the value of the commercial resistor differs too
much from the calculated resistance, connecting resistors in
series/parallel might help to obtain the precise required value.
Note 6: It is not recommended to set the Vset by dividing
the +12Vset voltage by a resistor divider. This setting is in
fact more complicated. Moreover, the stated accuracy toler-
ance of ±5 % for the overall control system may not be lon-
ger achieved because it is directly affected by the +12Vset
voltage tolerance which is ±10 %.
where Iout = 580 mA and Inom
max
= 700 mA
where Iset = 274 µA
and therefore Iout = 580.7 mA
Vset 1 + 9 8.33 V
Iout
Inom
Rset 30.87 kΩ
Vset
Iset
8.47 V