Newport 5600 Series - Io Lim; Vcomp

Chapter 3 Laser Diode Driver Operation 27
In the
Io
mode, the active set point is the actual drive current. A set point of
10A will cause the driver to drive 10A through the laser diode, assuming the
Io Lim
is set at or above 10A.
In
Im
mode, the set point is the desired amount of photodiode current, in
µ
A. Unlike the
Io
mode,
Im
mode will drive whatever current is necessary
though the laser diode, up to the limit, to achieve the set point photodiode
current.
Po
mode is simply an extension on the
Im
mode, allowing the user to
operate the system in milliwatts of power. The photodiode power set point,
in mW, is converted to photodiode current using the
PD Resp
value from the
setup menu.
3.5.3.2 Io Lim
As one of the safety features of the laser driver, the
Io Lim
sets a maximum
allowable current drive for the laser diode. The system will also limit current
set points to this value when operating in the
Io
mode. Two conditions can
be generated when the driver reaches this limit. The lesser of the two is the
soft current limit. The soft limit, indicated by
I
on the status line of the Laser
Main Screen, indicates that the laser driver is limiting the current drive to the
laser diode, but otherwise operating as normal. The second condition is a
hard limit, which indicates that the current drive attempted to exceed the
current limit faster than the circuitry could limit it. This condition causes the
laser driver’s output to be shutdown. Both of these conditions are monitored
in circuitry on the driver itself, and in the case of the hard limit, shutdown is
within microseconds of the condition being detected. See section 3.1.2 for
additional information on laser diode protection.
3.5.3.3 Vcomp
The voltage compliance setting controls the shutdown of the laser driver
output when the forward voltage of the laser exceeds the compliance setting.
Like the current limit described above, the voltage compliance is monitored
in circuitry on the driver itself, allowing for shutdown within microseconds
of the condition. See section 3.1.2 for additional information on laser diode
protection. The Vcomp setting may have to be increased when in pulse mode
or using square-wave modulation, due to driving cable inductance.
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com