13
Configuration Switch Bank:
This ten position switch bank configures the mode of operation (constant current or constant
power), the bandwidth of the output current, the range of photodiode sensitivity, and the
modulation transfer function.
Switches 1, & 2:
(Constant Current or Constant Power Mode of Operation
One of these
switches must be on for proper operation. The following chart shows the positions for both
modes of operation:
Mode
Switch 1
Switch 2
Constant Current
ON
OFF
Constant Power
OFF
ON
If both switches are accidentally left OFF, the output current will be shunted around the laser
diode by the output control shunt MOSFETs.
Switches 3, 4, & 5:
(330
µµ
F, 10
µµ
F, 1
µµ
F filter capacitors)
These switches select the type of
capacitive filtering across the laser diode load. All or none of these switches can be ON at one
time depending on the noise filtering and bandwidth requirements of the laser diode
application. A minimum of 0.1
µ
F capacitance is always present across the laser diode. The
output current bandwidth will depend on the total output capacitance and impedance of the
laser diode load.
Switch 6:
(Modulation Bandwidth)
When this switch in ON, a single pole filter with a 3dB
break frequency of 32Hz is inserted into the path of the setpoint control signal for the output
control loop. This limits the bandwidth of the modulation signal to a frequency of less than
32Hz. This is extremely useful for very low noise applications such as spectroscopy and
interferometry.
Switches 7 & 8
:
(2000
µµ
A or 200
µµ
A Photodiode Current Sensitivity)
This switch can configure
the photodiode transimpedance amplifier’s sensitivity. The following table shows the available
settings.
Sensitivity Range
Switch 7
Switch 8
50 - 2000
µ
A
ON
OFF
15 - 200
µ
A
OFF
ON
1 - 20
µ
A
OFF
OFF
To increase the range to 20mA, set the switch for the 2000
µ
A range and place a 10
Ω
resistor
across pins 5 and 6 of the Output Connector.
Switch 9:
(Modulation Sensitivity)
The modulation sensitivity can be controlled by this switch
position. The following table details the transfer functions for each model:
Switch 10:
(Modulation Input Enable)
This switch is used to enable or disable the modulation
input. When this switch is OFF, the modulation input is disabled and the output cannot be
controlled from the BNC or the Analog Interface Connector. When this switch is ON, the
modulation input is enabled and the output can be controlled by these external analog inputs.
If both switches are accidentally left ON, it is possible that
the laser diode forward current could reach the Limit Current
Setting.
NOTE!