LD2000(R)
0187-D01 Rev F, 3/22/2011
Page 9
www.thorlabs.com
Setting the Feedback Resistor
The LD2000 is configured at the factory for a maximum feedback gain. This gain setting
is appropriate for lasers that have low monitor currents in the range of 20 to 120
μ
A.
For most lasers, the photodiode current is greater than 120
μ
A and the feedback gain will
have to be reduced to drive the laser at full drive current. This can be done by following
the procedure below.
1.
Determine the appropriate feedback gain using the following calculation:
20,000
8,000
1
where R
F EXT
is the external gain setting resistor to be added in ohms and I
MON
is the monitor current for a particular laser in Amps.
2.
Pick the nearest standard value resistor (0.25 W, 5% or better).
3.
Connect R
F EXT
across pins 8 and 12 of the LD2000.
WARNING
The LD2000 uses CMOS circuitry to minimize power drain. Use
anti-static precautions while handling the LD2000 to prevent
permanently damaging the device.
0.1
1
10
0.1
1
10
100
1 10
3
RFext vs. PD Monitor Current
PD Monitor Current (mA)
R
Fext (kohm
s)
!
!