Doc 2136-D01 Rev E 1/24/02
2-5
2-5
If other laser diode mounts are used, connect the laser diode and, if provided, the photodiode with shielded cables to
"LD OUTPUT" (5) according to the pin assignment shown in Fig 2.3.
pin
connection
open circuit monitoring, status display:
1
interlock
5
digital ground for pin 1
laser
diode:
7
laser diode cathode (laser anode is at ground)
8
laser diode anode (laser cathode is at ground)
3
ground for the laser diode
photodiode:
2
photodiode
cathode
4
photodiode
anode
Fig. 2.3
Pin assignment of jack "LD OUTPUT"
Selecting the laser pins to use:
Determine which laser pin (anode or cathode) is attached to your laser package. This will be connected to pin 3. If the
floating laser pin is the cathode attach it to pin 7 and leave pin 8 unconnected. If the floating pin is the laser anode,
attach it to pin 8 and leave pin 7 unconnected.
Safety Interlock
Pin 1 and pin 5 of the LD OUTPUT jack (5) are contacts to allow for an optional externally connected Interlock
switch. Open contacts on this switch will prevent the unit from operating or shut the unit down if it is already
operating. The unit can only be Enabled if the switch contacts are closed.
If no interlock switch is used, this feature can be bypassed by connecting Pin 1 to Pin 5 with a wire as shown in Fig.
2.4.
Connecting the laser diode and photodiode
Connect laser diode and photodiode according to Fig. 2.4 to the LDC 500.
The ground connection of the laser diode (pin 3) may be connected to the anode of the photodiode (pin 4) or to the
cathode of the photodiode (pin 2). This connection should be as close as possible to the laser diode to avoid
measurement errors.
If the polarity selected with the switch "LD POL" (6) and the connection of the laser diode do not agree, no current
will flow through the laser diode.
The laser diode is always driven with respect to ground. Compared to a floating driver stage, this operating mode has
the advantages of higher security for the laser diode and better stability of the laser current.
