Automatic Constant Power Control (Apc) - THORLABS IP500 User Manual

IP500 Laser Diode Controller
If the ALARM indicator turns ON see Section 2.3 "Alarms and Troubleshooting" on
Page 7.
Note: If the ILIM setting is below approximately 10 mA the I LIMIT LED will be ON,
this is normal.
If the current is adjusted to its maximum limit then the I LIMIT indicator will turn
ON. This indicator is active when the injection current is approximately 95% of the
maximum limit.
If the photodiode is connected and the PLIM is set to a value requiring less than
the maximum current set by ILIM, the I LIMIT indicator will NOT turn ON and the
unit will operate in constant power at the power limit level set by PLIM.
While operating in APC Mode, if the power is adjusted to its maximum limit then
the injection current will not increase even though the potentiometer has more
adjustment.
If the PLIM is set to a value that requires a higher level of drive current than ILIM
is set to, the I LIMIT indicator will turn ON and the unit will operate in constant
current at the current limit level.
2.2.2.

Automatic Constant Power Control (APC)

Photodiode feedback current is required in APC mode.
Set JMP1 to either "AG" for Laser Diodes with Grounded Anodes or "CG"
1.
for Laser Diodes with Grounded Cathodes. JMP1 is located on the left
side of the unit. Always disable the laser driver prior to changing modes.
Set JMP2 to "APC" for Constant Current operation. JMP2 is located on
2.
the left side of the unit. Always disable the laser driver prior to changing
modes.
3. Apply power to the unit.
4. Using a digital multimeter measure the ILIM Test point with respect to the
TP GND Test point (all measurements will be with respect to TP GND).
Adjust the ILIM ADJ potentiometer to the maximum laser current limit.
The transfer function is 1 V = 1 A, with a maximum adjustment of
approximately 0.500 V or 500 mA.
When operating in APC the ILIM (current limit) function is still active if the
laser current reaches the limit point.
5. Measure the PLIM Test point and adjust the PLIM ADJ pot for the
maximum MPD current expected. The transfer function is 1 V= 1 mA, with
a maximum adjustment of 2.5 V or 2.5 mA.
6. The P/I ADJ Pot will allow adjustment of the Monitor Photodiode current
from 5 uA to the PLIM set point or 2 mA max. When turning on a laser for
the first time it is suggested that this pot be set fully counter-clockwise.
7. Press and release the ENABLE switch.
Rev I, December 1, 2015
Chapter 2: Setup and Operation
Page 5