Wavelength Electronics PLD K-CH Series, Datasheet And Operating Manual

Page: 14 / 24

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PLDXK-CH SERIES LASER DIODE DRIVER
ADJUST THE OUTPUT CURRENT SETPOINT—
ONBOARD CONTROL
To increase the output current, turn the onboard trimpot
clockwise; turn counter-clockwise to decrease output
current.
While adjusting the output current, measure the voltage on
pin J2:4, IMON. Use the transfer function listed in Table 2 to
determine the output current from the monitor voltage.
ADJUST THE OUTPUT CURRENT SETPOINT—
ANALOG INPUT
To use ANALOG IN (pin J3:5) to adjust the output current,
refer to Pin Descriptions on page 4 for specifications.
The analog input signal sums with the onboard trimpot
value.
The analog input signal can be used whether the driver is
operating in Constant Current or Constant Power mode.
Refer to Table 2 on page 5 for the transfer functions for
CC and CP modes.
Refer to the External Setpoint Circuit on page 16 for an
example analog input circuit. Other circuits, a DAC signal,
or function generator may be used. The analog input pin is
not designed for use with TTL signals.
COMBINING THE ONBOARD SETPOINT AND
ANALOG INPUT
The ANALOG IN voltage signal on J3:5 sums with the
onboard trimpot setpoint. This configuration allows the
driver to be configured so that the laser current or power
modulates around a DC setpoint.
If the sum of the two signals causes the PLDxK-CH to
attempt to drive the output current past the limit, the output
will switch off and indicate a current limit error.
To avoid driving the current to the limit, first set the onboard
trimpot to produce the Constant Current level. Then connect
the modulation source to the ANALOG IN pin and slowly
increase the modulation amplitude. Monitor the output
current using the IMON pin, or by measuring the voltage
across the test load. Do not monitor the voltage across a
laser diode—measurement transients may damage the
laser diode.
CURRENT LIMIT CIRCUIT TRIGGER AND RESET
If the PLDxK-CH detects current limit, the output will
switch off and the I DISABLED LED on the top of the unit
will illuminate red and the
LD Status
voltage will drop to
ground. Set the Enable switch to OFF, correct the cause of
the error, and then re-enable the output.
MONITOR THE PHOTODIODE CURRENT
If the photodiode is connected to the PLDxK-CH, the
current can be monitored by connecting a multimeter to the
PMON pin, J2:3, and reading the voltage. Refer to Table 2
on page 5 for the transfer function to convert the PMON
voltage to PD current.
When using Type C lasers, the PD Range switch must be
set to LO.