Switching Buck Regulator against Constant Current Driver.

[Harsh Chandola]

Hello All,
I am designing a tube light that can switch between warm white, cool white and both warm and cool white depending on the way push button is pressed, single short press toggles between warm and cool white and long press turns both ON. For this circuit I am using Atmega328P as the micro controller to perform the task. The circuit I have designed will be fed with existing tube-light LED driver. Now the specification for LED Tube light would be in the range of 48-72 volts and upto 250mA for each cold white and warm white strip. My first hurdle is how to feed 5volts to Atmega328P chip. While I designed the circuit I didn't take into account the driver I'd cascade with my circuit would be a constant current driver. So assuming constant voltage driver I chose MAX5035 BUPA+ Switching Buck Regulator that can regulate voltages up to 76 volts to 5Volt and rest of the circuitry is easy.
Now suddenly I thought, I might have to use constant current driver and now I am confused about how will my Regulator be regulating voltage if it's constant current that comes out of the driver. Is there a simple work around that can be implemented.
 
I'd be obliged if somebody explains me constant current drivers and constant current source's concept in detail and in almost layman's terms if possible, with schematic and all.

Please find attached the schematic for my design.
D1 and D2 are Zener diodes.
Kind Regards,
Harsh Chandola

[danadak]

The Atmega wants to be driven with a constant V. That takes care of
device to device and I/O load variation, eg. if load changes device V
stays the same, in spec.

A constant I driver, for load changes, supplies a fixed current. LEDs
like to be driven as constant I so that led to led in a given strip put
out roughly same brightness, and are invariant to led to led manu-
facturing parameter differences.

Note your tube may incorporate internally a constant current driver.
Hence its input, a V, feeds constant current driver input. Some really
cheap strips just use a R to effect a crude constant current. But LED
device threshold, led to led, vary all over the map.


Regards, Dana.

[Harsh Chandola]

The Atmega wants to be driven with a constant V. That takes care of
device to device and I/O load variation, eg. if load changes device V
stays the same, in spec.

A constant I driver, for load changes, supplies a fixed current. LEDs
like to be driven as constant I so that led to led in a given strip put
out roughly same brightness, and are invariant to led to led manu-
facturing parameter differences.

Note your tube may incorporate internally a constant current driver.
Hence its input, a V, feeds constant current driver input. Some really
cheap strips just use a R to effect a crude constant current. But LED
device threshold, led to led, vary all over the map.


Regards, Dana.

I understand that, my other question is can I use switching buck regulator like MAX5035 to convert current to voltage and then snap it down to 5Volts so that I'll be able to power Atmega? Is that possible? or is there a work around to get that done?