Power Supply Connection; Laser Current Limitation; Laser Current Monitoring; Cp Feedback Loop Compensation - THORLABS MLDEVAL User Manual

MLDEVAL

2.1 Power Supply Connection

The MLDEVAL comprises an integrated active circuit that automatically switches between the
two available power sources. In the case that both the USB and the external power supply is
connected to the MLDEVAL, it will automatically use the external power supply. The protection
circuit features also a reverse voltage protection and a reverse current blocking.

2.2 Laser Current Limitation

In some specific applications it might be useful to to limit the laser injection current, for ex-
ample, for very low power laser diodes, particularly when they will be operated in CC mode.
This limitation is achieved by inserting a resistor R1 next to the jumper JP1 into the output cur-
rent path. Its resistance is calculated to
with U - compliance voltage of the used MLD203xxxE module. The compliance voltage
C
ranges from 3 V to 4 V, depending on the operation point. The minimum operating current
should be measured for each application separately.
U - forward voltage of the laser diode at its maximum allowed injection current I
LD
Solder an SMD resistor of the calculated value, with 1206 or 0805 footprint to the position R1.
Remove the connected in parallel jumper JP1 to enable the current limitation.

2.3 Laser Current Monitoring

The laser diode current can be monitored at the J6 Mon. Current Connector (13) by measuring
the voltage at this connector. The conversion coefficient is 1 V/A, so the current is calculated by

2.4 CP Feedback Loop Compensation

Note
Only for MLD203P1E and MLD203P2E !
The control loop of the MLD203P1 and MLD203P2 are optimized for standard TO Can laser di-
odes. When using different lasers with different photodiodes it might become necessary to
compensate the parasitic capacitance of the used photodiode. The parasitic resistance and
parallel capacitance of the used photodiode results in a time constant. To compensate the con-
trol loop we recommend to match the time constants of the photodiode with the time constant
of the used module.
This can be done by adding a SMD capacitor ( Footprint 0603 or 0805) to position C4 located
on the MLDEVAL PCB between J7 and J9.
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LD,MAX
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