OSRAM OPTOTRONIC Constant current LED power supplies with 3DIM - Manual (Page 38)

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3.3.2.3. Application solution 3 –
overtemperature management: continuous derating and switch-off
The following application shows a cost-effi cient solution obtained by using a low-
cost dual OPAMP (such as LM2904). The idea is to manage the overtemperature
state of the LED module by continuously derating the current in a defi ned temp e-
rature range (from Tset
L
to Tset
H
), ending with the switch-off of the supply output
current when the protection temperature is reached (Tset
H
). The design of the
circuit becomes a bit more complicated but the solution is very cheap and only
requires about 15 components which do not take up a lot of space.
LEDset APPLICATIONS
Figure 35: Thermal derating –
NTC + OPAMP solution: continuous derating and switch-off. Figure 36: Thermal derating –
NTC + OPAMP solution: continuous derating and switch-off characteristic.