I have 2 nos 7W LED Modules, each of which are fed from a separate XL6001 based LED Driver. The DC power input to the drivers is from a 12V, 7.5AH SLA Battery. The LED driver takes 12V DC from the battery and boosts it to 22V DC for the LED module. The current consumption at the lamp side is 636mA (for both lamps), while on the battery side is upwards of 1.2A (for both lamps). All this works fine.
Now, in a separate mode of operation, I would like these lamps to light up from AC power. The design of the operating unit (the overall box) is such that power must go through the LED drivers to reach the lamps. So, for the AC power mode, I have been trying to use an LM317 voltage regulator outputting 12V DC which is then fed to the above LED drivers. I am observing that after a few minutes the output of the LM317 drops to 4.5V DC and current falls down to 300mA (for both lamps) on the input of LED driver. This results in "abysmal" brightness from the lamps. I have also tried using an LM350 (3A rated) and found the same sudden voltage drop.
What am I missing? Is it heatsinking...though I am using a regular heatsink which is used with TO-220 packages. Ambient is around 28 C.
Should I configure LM317 as a constant current source and then feed its output to the LED driver ?
Should I configure the output voltage from LM317 to be 22V and then feed it to the LED driver ?
The input to voltage regulator is from the bridge rectified output of a 230V:24V single phase, 50VA transformer.
Thanks and best regards,