Setting The Feedback Resistor - THORLABS EK2000 User Manual

OEM Laser Diode Driver Evaluation Kit
4.5.1.

Setting the Feedback Resistor

The LD2000R 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 A.
For most lasers, the photodiode current is greater than 120 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:
where R
and I
MON
2. Pick the nearest standard value resistor (0.25 W, 5% or better).
3. Connect R
3
1 10
100
10
1
0.1
0.1
The LD2000R uses CMOS circuitry to minimize power drain. Use anti-static
precautions while handling the LD2000R to prevent permanently damaging
Page 15
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is the external gain setting resistor to be added in ohms
F EXT
is the monitor current for a particular laser in Amps.
across pins 8 and 12 of the LD2000R.
F EXT
RFext vs. PD Monitor Current
SHOCK WARNING
20,000
=
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( 8,000��
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1
PD Monitor Current (mA)
the device.
Chapter 4: LD2000R Overview
− 1 )
Rev F, May 21, 2018
10