OSRAM OPTOTRONIC Constant current LED power supplies with 3DIM - Manual (Page 33)

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Figure 26: Two-step solution without switch-off.
3.3.1.7. General notes on IC temperature switches:
choice and usage
• For all the above application solutions, the Rset can be
either a fi xed resistor or a variable resistor usable for local
dimming (as described in 3.2.).
• For all the above application solutions except application
solution 6, the output of the IC (direct output or output via
transistor) can be connected to the Vset line via an Rset
2
resistor. In this way, in case of overtemperature, the output
current can be set to a percentage of Inom
max
instead of
completely switching off the LED module as shown in the
example cases. Application solution 6 allows implementing
both conditions, partial load and switch-off control.
• When choosing IC temperature switches, the following
issues must be considered:
– Leakage current of the output stage of the control
module: In case of an open-drain output solution directly
connected to Vset, the leakage current should be as low
as possible (10 µA already lead to an error of 3 %) in
order not to affect the overall control accuracy.
– Supply voltage: If the IC cannot withstand the +12 V,
a voltage regulator must be used.
– Supply current: In LEDset ECGs of the fi rst generation,
the supply current provided by the +12Vset terminal must
be kept lower than 15 mA.
– Transistor output solution:
- Suitable if the maximum voltage of the output pin of the
IC cannot withstand the maximum Vset that applies to
the respective application.
- Suitable if the leakage current of the output pin of the
IC becomes too high (a leakage current of more than
10 µA affects the overall control accuracy of the ECG by
3 % (to be added to the 5 % of the ECG itself).
LEDset APPLICATIONS