OPERATIONS
Functions and Features
7/01 LDC-3700 Series 33
CHAPTER 2
indicator is illuminated. Repeatedly pressing the (LASER MODE) SELECT switch cycles through
the current (I), light power (P), or high bandwidth current (I
HBW
) control modes.
Set the laser controller’s current source range by selecting the 200 mA range indicated by the
accompanying LED. You will need to press the select push button twice to change the range. It
must be pressed twice quickly (within less than 1 second) to switch between modes, and the LASER
output must be off (LASER MODE ON indicator unlit) in order to change ranges.
The limit clamp function for DC output current applies to the modulated current as well protecting
your laser in any mode. To accomplish setting the current source limit, use the SELECT push
button in the PARAMETER/LASER section of the front panel to select LIM I. You will notice there
are two LIM I selections, one in blue text and the other in black text. These limit selections
correspond to the current source range as indicated in the RANGE section. When the blue LIM I is
indicated by the accompanying LED, the LASER display will be indicating the limit set point in mA
for the controller’s low range. Press the (PARAMETER) SET push button and rotate the adjust
knob, clockwise to increase the limit set point value, or counterclockwise to decrease the limit set
point value. Set the limit to 175 mA. Once the SET push button is released, the new parameter
value is stored in non−volatile memory.
When the laser current limit is reached, the CURRENT LIMIT error indicator flashes. The current
limit setting is independent of the voltage drop of the device connected to the laser output, and
therefore, no dummy load is required for precise adjustment of the current limit. Furthermore, since
the current limit circuitry is fully independent of the main current control, the current limit can be
adjusted safely, even while the LASER output is active.
Now you are ready to modulate the laser injection current. To enable the controller output, in the
LASER MODE section of the front panel, press the push button labeled OUTPUT. The
accompanying LED labeled ON will illuminate indicating that the laser current source’s output is
enabled. The instrument will drive the current source to the value set by the corresponding LASER
MODE set point . When the LASER output is off, an internal short is placed across the laser output.
ON
OUTPUT
I
HBW
I
SELECT
LASER M ODE
PRESS TW ICE
200 mA
500 mA
RANGE
LIM I
TE
SAVE
CONST
LIM T
HI
TEC
CAL PD
RECA LL
SET
SELECT
PARA M ETER
LASER
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