2 – 16
Getting Started
will exit “live” mode.
The output current limit can be changed at any time. If the limit is
changed to be smaller than the present value of the laser current, the
setting will be “dragged” along with the limit value downwards.
Changing the voltage limit is allowed at any time. If the voltage limit
is changed to be smaller than the present value of the laser operating
voltage, the laser driver will immediately trip o
ff
.
2.3.4
Operating the laser in CP mode
To operate in CP (constant power) mode, a photodiode must be con-
figured for the LDC500 to measure the laser optical power. This
configuration includes the photodiode reverse bias voltage, respon-
sivity value, and display units.
•
Beginning with the LD driver o
ff
, select CP mode by pressing
[Current
/
Power]. The mode indicator switches between
CC
and
CP
.
•
Press [Config], and navigate with [ ] and [ ] to the menu item
“LD Cfg: PD units.” To control the laser in (optical) milliwatt
units, set “use mW:” to “Y”; to control the laser in raw mi-
croamperes of photodiode current, set “use mW:” to “N.” For
this example, select “N.”
•
Press [ ] to select “PD Bias:”, and set the photodiode reverse
bias between 0.0 V and 5.0 V.
•
If you know the photodiode responsivity (in
μ
A
/
mW), you can
enter the value directly by pressing [ ] twice to navigate to the
“LD Cfg: PD resp” item.
•
If you do not know the responsivity, leave the responsivity
value unchagned and be sure to set the “PD units” item to
“use mW: N.” See section 2.3.7 for how to use the LDC500 to
calibrate a photodiode responsivity.
•
Press [Set] to select the LD Settings menu tree, and navigate
with [ ] and [ ] to the “LD Ilim:” item. This sets the
laser
diode
limit current, and should be adjusted to ensure the safe
operating current of the laser diode is never exceeded.
•
Press [ ] repeatedly to select “LD Vlim:”, and set this to the safe
maximum operating voltage for your laser diode.
•
Press [ ] to select “PD Ilim:”. This item is the
photodiode
limit
current, and corresponds to the maximum setpoint value that
can be entered in CP mode. Note that the LD driver can be
LDC500 Series Laser Diode Controllers
