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All   >>  LED Lighting   >>   General Lighting Applications   >>   Questions
 

Are you offering CCR LED drivers with thermo-management functionality? Respectively, could you please suggest thermo-management circuitry for CAT4101?

The first thought uses our Adjustable current feature on the CCR and the other ones would be perfect with our new NSI45019JPT1G (not RTM right now, but engineering samples are available). \n\n1.) Use a PTC Thermistor on the RADJ pin of the CCR.\na. This is the cheapest solution, but the Real issue when using this approach is that you will not get full current turn off. As the CCR gets hot it will reduce the current then as the RADJ gets a larger value it will clamp the current even more, but it still may only get you down to maybe -30% of the low side current range.\n2.) Use a voltage divider with an NTC thermistor that feeds into the Base of a transistor or the gate of a FET.\na. If the Thermistor is placed on the low-side of the divider then the base drive will drop and turn off the transistor/FET.\nb. As you could see the issue would be then as the input voltage to the divider is low then the LED string is not on.\nc. Also as the input voltage to the divider is high the NTC Thermistor will have to have an even greater delta.\n3.) Use two dividers and feed them into a comparator to turn off a transistor and turn off the LED string.\na. This is basically a discrete approach similar to that the internals of the LM3424 is doing.\ni. You can use either a Resistor divider OR a NSI50010YT1G that feeds a zener as stiff reference voltage.\nii. Then a resistor and a NTC Thermistor as thermal sense voltage.\nb. These two inputs can feed into a comparator and as the thermal sense voltage starts to drop then the comparator will put out a high voltage and this can be used to turn off a PNP or any high side switch in series with the CCR and LEDs. Answered by:
ON Semiconductor
2011-06-02 19:12:57.0