If you used a 34063 IC as a SMPS IC it has one resistor that sets the current limit, and it will happily drive a power LED as a constant current SMPS buck driver.

Does not have a high voltage version. Can't easily be used for 1.5A or 2A.

 

I have connected the LEDs. Actually maximum current is 1.5 Amps when I turn the feedback resistor fully to ground. Maybe due to the inductor value?

I added 12 turns to a toroid. Previously it had 100 turns/680uH.

Input voltage: 32V
Output voltage ~24V

But I adjusted it to 1.3A for the time being.

 

I've seen in some datasheets 60ºC as the maximum recommended temperature, but the actual temperature of the die is gonna be hard to know without knowing the thermal resistance of the device.
...

I just point the infrered thermometer at the device. Semiconductor plastic is quite transparent (transmissive?) to IR heat energy so the IR thermometer measures the IC silicon temperature.

It's interesting with some TO220 FETs etc to measure the heatsink tab at 55'C but the silicon FET itself is shining brightly at 70'C, 80'C or more...

 

I just point the infrered thermometer at the device. Semiconductor plastic is quite transparent (transmissive?) to IR heat energy so the IR thermometer measures the IC silicon temperature.

It's interesting with some TO220 FETs etc to measure the heatsink tab at 55'C but the silicon FET itself is shining brightly at 70'C, 80'C or more...

Correct, the cooler grid for a IRF MOSFET will reach 105C, and this is about the point where it will latch from heat.

So as a rule of thumb, cooler grid temp. must always be less than boiling point of water.

If any possible, it should not allowed to get hotter than the temp. which is still possible to touch permanently. A little more is OK so it's just uncanny to touch it, but not much more.

I have done a lot of experimentation using a very small NTC sensor + digital thermometer. EMF was so bad I had to inline coils, otherwise the thermometer would hang up and would need a hard reset.

 

I just point the infrered thermometer at the device. Semiconductor plastic is quite transparent (transmissive?) to IR heat energy so the IR thermometer measures the IC silicon temperature.

It's interesting with some TO220 FETs etc to measure the heatsink tab at 55'C but the silicon FET itself is shining brightly at 70'C, 80'C or more...

Oh nice =)