IP500 Laser Diode Controller
Chapter 2: Setup and Operation
Page 6
3037-D02
8. The green LD ON indicator will turn ON. If the ALARM indicator turns ON
see “Alarms and Troubleshooting” below. If the I LIMIT indicator turns ON
immediately press the ENABLE switch and refer to “Alarms and
Troubleshooting”.
9. Adjust the P/I ADJ potentiometer clockwise to increase the MPD current.
The IPD Test point provides an analog read back of the actual MPD
current, 1 V = 1 mA.
10. Pressing the ENABLE switch while the laser is operating will turn off the
laser current.
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.
If the photodiode is connected incorrectly or the connection is opened, the I LIMIT
indicator will turn ON and the unit will operate in constant current at the current
limit level.
2.2.3. Analog Modulation
The amplitude of the laser injection current can be varied over time by connecting
a signal generator to the BNC connector J3 on the IP500. It is recommended that
the unit be configured to operate in ACC mode whenever analog modulation is
used.
J3 can also be used as a remote analog input, allowing the user to program the
laser injection current from 0 to 500 mA by applying a 0 to 10 VDC signal. The
transfer function being 50 mA per 1 V.
The P/I ADJ pot must be set fully counter-clockwise prior to using this input.
For 100% depth of modulation set the P/I ADJ pot fully counter-clockwise and
apply a sinewave input to J3. The peak-to-peak amplitude must equal ILIM / 0.05
and a DC offset equal to 0.5 of the amplitude must be applied (the signal should
always be above 0 V).
The depth of modulation can be decreased by increasing the P/I ADJ pot to provide
a DC current offset, and then adjusting the peak-to-peak amplitude to stay within
the ILIM range. The ILIM circuit will limit the average current to the ILIM setting
and the I LIMIT indicator will turn on when the average current exceeds the ILIM
setting.
The ILD Test point will provide the average current level when modulating.
