THORLABS LD3000R User manual

LD3000R
Constant Current Laser
Diode Driver
User Guide

Constant Current Laser Diode Driver
Table of Contents
Chapter 1 Warning Symbol Definitions ...........................................1
Chapter 2 Description........................................................................2
Chapter 3 Setup and Operation........................................................3
3.1. Laser and Power Supply Connection ..............................5
3.2. Selecting External Current Control Mode .......................6
3.3. Laser Current Monitor ...................................................6
3.4. Photodiode Current Monitor .........................................7
3.5. Important Note About Compliance Voltage and Power
Supply Voltages ............................................................8
Chapter 4 Specifications.................................................................10
Chapter 5 Drawings .........................................................................11
Chapter 6 Regulatory.......................................................................12
Chapter 7 Thorlabs Worldwide Contacts.......................................13

Constant Current Laser Diode Driver Chapter 1: Warning Symbol Definitions
Rev K, March 27, 2017 Page 1
Chapter 1 Warning Symbol Definitions
Below is a list of warning symbols you may encounter in this manual or on your
device.
Symbol
Description
Direct Current
Alternating Current
Both Direct and Alternating Current
Earth Ground Terminal
Protective Conductor Terminal
Frame or Chassis Terminal
Equipotentiality
On (Supply)
Off (Supply)
In Position of a Bi-Stable Push Control
Out Position of a Bi-Stable Push Control
Caution: Risk of Electric Shock
Caution: Hot Surface
Caution: Risk of Danger
Warning: Laser Radiation
Caution: Spinning Blades May Cause Harm

Constant Current Laser Diode Driver Chapter 2: Description
Page 2 16512-D02
Chapter 2 Description
The LD3000R was developed for operating laser diodes in a constant current
mode, up to a maximum of 2.5 A. It allows the laser anode to be grounded while
operating off a negative DC supply, allowing lasers whose anodes are connected
to the laser case to be mounted in a grounded case for added ESD protection. The
laser operating current can be set with either an on-board 12-turn trimpot or an
external analog voltage (0 to 5 VDC).
The LD3000R has a quiescent laser current of 10 to 20 mA (i.e. with the laser
current control turned down to a minimum, the lowest laser current could be as
high as 20 mA). If your laser has an operating current of less than 100 mA, we
recommend using Thorlabs’ LD1255R Laser Driver, which has a lower quiescent
current and will offer better current control at the lower operating currents.

Constant Current Laser Diode Driver Chapter 3: Setup and Operation
Rev K, March 27, 2017 Page 3
Chapter 3 Setup and Operation
The LD3000R was designed to mount to a suitable heat sink. Two counter-sunk
clearance holes located on 3" (76.2 mm) centers are provided for easy mounting.
WARNING
The driver dissipates a large amount of heat when driving lasers under full
load. To avoid permanent damage, do not operate the driver without a heat
sink.
There are two single-row connectors located on top of the unit. The 10-pin
connector is used for the power supply input, the laser interface, and monitor
signals. The table below lists the pin configuration of J1:
Pin #
Function
1
+V (5 to 12 VDC, 50 mA)
2
Ground
3
-V (-8 to -12 VDC, 2.5 A)
See Page 8 for Notes on Compliance Voltage
4
External Current Control (0 to 5 VDC)
5
No Contact (Polarization Key)
6
Laser Diode Anode (Internally Connected to Pin 2
Ground)
7
Laser Diode Cathode
8
Monitor Photodiode Anode (from Laser)
See Caution Below
9
Photo Diode Monitor Output (-1 V/mA)
10
Laser Current Monitor Output (1 V/A)
Referenced to -V
CAUTION
The PD monitor circuit of the LD3000R only supports lasers that have an
isolated PD anode. It will not work with common cathode lasers.
CONNECTING THE PHOTODIODE OF THESE LASERS TO THE LD3000R WILL
DESTROY THE LASER.
The LD3000R will operate the LD portion of all common cathode lasers
without issue as long as the PD anode is not connected to the driver.

Constant Current Laser Diode Driver Chapter 3: Setup and Operation
Page 4 16512-D02
The pin configuration for the 5-pin connector J2 is given in the table below.
Pin #
Function
Jump 2 to 3
Mode 1: COMMON Referenced External Current Control
Jump 4 to 5
Mode 2: Disable External Current Control
1
No Connection (Leave This Pin Floating)
5
-V (May Also Be Used for Monitoring Signals)
CAUTION
Do not operate the LD3000R without a jumper installed on J2. Your laser may
be overdriven and permanently damaged.
WARNING
Direct viewing of laser diode emission may cause eye damage, especially in
conjunction with collimating lenses. Extreme care must be taken to prevent
any beam from being viewed directly or indirectly through external optics or
mirrors.

Constant Current Laser Diode Driver Chapter 3: Setup and Operation
Rev K, March 27, 2017 Page 5
3.1. Laser and Power Supply Connection
The LD3000R requires a clean (preferably non-switching) DC bipolar power supply
for optimum operation. The positive supply is used only for biasing low-power
amplifiers and only needs to supply 10 mA of current. The laser drive current is
derived from the negative power supply output and should be capable of at least
-2.6 A of current.
1. Attach the DC power supply to J1 according to the table on page 3.
2. Attach the laser diode to J1 according to the table on page 3.
3. Select the desired current control mode using J2 (see Section 3.2 below).
4. Turn the current control potentiometer a full 12 turns counterclockwise to
ensure the laser current is at aminimum. (Note that the potentiometer will
continue to turn after reaching the limits. To be safe, always turn the
potentiometer at least 12 complete turns to ensure the current is at its
lowest setting.)
5. Apply power to the LD3000R and slowly turn the current control
potentiometer clockwise until the desired operating current is achieved.
Connect a DVM from Pin 10 of J1 to Pin 3 of J1 (Pin 5 of J2 may also be
used) to monitor the laser current. Note that Pin 3 is connected to the
negative voltage supply. If using a DAQ card, make sure these specs will
not damage it.

Constant Current Laser Diode Driver Chapter 3: Setup and Operation
Page 6 16512-D02
3.2. Selecting External Current Control Mode
The current can also be externally controlled by a voltage source applied to J1 pin
4 (function generator, DAQ output, etc.). The external current control voltage must
be referenced to the common output of the power supply. The total drive current
is determined by the sum of the manual set point and the external current control
voltage.
CAUTION
One of the following operating modes must be selected BEFORE turning the
LD3000R on. Otherwise, the laser will be overdriven and damaged.
Mode 1
COMMON referenced external current control voltage (i.e. 0 to 5 V). An internal
level shifter allows the negatively biased laser to be controlled by a COMMON
referenced control voltage. To enable this mode jumper pin 2 to 3 on J2.
In Mode 1, the laser current is:
  

Mode 2
If the External Current Control is not to be used, disable by jumpering pins 4 and
5 on J2.
3.3. Laser Current Monitor
The laser drive current can be monitored from pin 10 of J1. This output is
referenced to the negative supply (J1 Pin 3 or J2 pin 5) and has the following
transfer function:
   󰇛󰇜
Using a DVM, the laser current can be read without having to compensate for the
negative voltage offset by attaching the (-) lead to J1 Pin 3 and the (+) lead to J1
pin 10.

Constant Current Laser Diode Driver Chapter 3: Setup and Operation
Rev K, March 27, 2017 Page 7
3.4. Photodiode Current Monitor
CAUTION
The LD3000R has a photodiode monitor circuit that only supports lasers
having the laser anode attached to the photodiode cathode. The use of the
monitor input with common cathode lasers will cause damage to the laser.
However, the LD3000R can be used safely with common cathode lasers as
long as the photodiode is not connected to the driver.
An on-board transimpedance amplifier is provided for lasers with internal monitor
photodiodes that are supportedby theLD3000R (see cautionabove). The amplifier
converts the photodiode current to a voltage that can be measured on J1 Pin 9 for
monitoring the relative laser output power. The output of pin 9 has the following
transfer function:
  󰇛󰇜
If the exact monitor current is known for a given laser power, this output can be
converted to laser power as follows:
   

Where is the monitor photodiode conversion factor (mW/mA).
CAUTION
The LD3000R operates diode lasers only in a constant current mode. Caution
must be used to avoid overdriving the laser when operating the laser over
widely varying temperatures. Diode lasers become more efficient as their
operating temperature decreases. It is possible to overdrive the laser when
operating the laser near the maximum drive current if the laser temperature is
lowered. Please consult the laser manufacturer’s data sheets.

Constant Current Laser Diode Driver Chapter 3: Setup and Operation
Page 8 16512-D02
3.5. Important Note About Compliance Voltage and Power
Supply Voltages
The LD3000R is a power module and will dissipate a fair amount of heat under
normal operation. However, it is imperative that the driver be mounted to an
adequate heat sink to avoid damaging the internal components. Also, please read
the following section on compliance voltage to keep the excess heating to a
minimum.
One of the most important specs of a constant current source is its compliance
voltage. This is the maximum voltage a current source can supply to a given load
at a given current. The higher the load impedance is, the higher the compliance
voltage must be to operate as a constant current source. Because of the
LD3000R’s internal impedances, this compliance voltage depends on the
operating current and decreases as the current increases. The compliance voltage
can be easily calculated as follows:
   󰇟󰇛󰇜  󰇠
Where:
 = compliance voltage
 = the negative supply voltage (this is the input power for the LD3000R)
 = the operating current of the laser
 = minimum output transistor voltage (set this to 1.8 V to solve equation)
 = the forward operating voltage of the laser diode. (Typically 2 to 3 V)
A couple of important points:
1. VCOMP must be positive.
2. As Vss increases, the compliance voltage increases.
3. If Vss is too high, the LD3000R will dissipate the excess energy as heat.
Example 1
ILD = 1 A (laser operating current)
VLD = 2 V (laser forward voltage)
Vss = 12 V
  󰇟󰇛󰇜  󰇠 
The compliance voltage should be limited as much as possible since the excess
compliance voltage results in unnecessary heating:
 󰇛󰇜
  󰇛󰇜 
A better way to approach the question is to calculate the minimum negative supply
voltage necessary to operate the laser. This will keep the excess heat build up to