42 Chapter 3 Laser Diode Driver Module Operation
3.6.9 Constant Current, High Bandwidth Mode
This mode of laser operation is shown in Figure 21. In this mode, current feedback is
used to control the laser output. The bandwidth is between 50 kHz and 500 kHz,
depending on the model.
3.6.10 Constant Current, Low Bandwidth Mode
This mode of laser operation is shown in Figure 22. In this mode, current feedback is
used to control the laser output.
In this mode, capacitors are switched into the circuit. These capacitors act as a filter
and therefore prevent the laser output from changing too rapidly. This gives added
laser diode protection. This also limits the laser output bandwidth to about 10 kHz.
In the Low Bandwidth - CW mode, the bandwidth is further limited to 30 Hz.
Unregulated DC
Voltage
Regulator
Pass
Transistor
Modulation
Input Port
Current Set Point
Laser Diode
Current
Sense
Output
Shorting
Figure 21 - Constant Current - High Bandwidth Mode
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