THORLABS LD3000R Manual de usuario

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

+V (5 to 12 VDC, 50 mA)

Ground

-V (-8 to -12 VDC, 2.5 A)

See Page 8 for Notes on Compliance Voltage

External Current Control (0 to 5 VDC)

No Contact (Polarization Key)

Laser Diode Anode (Internally Connected to Pin 2

Ground)

Laser Diode Cathode

Monitor Photodiode Anode (from Laser)

See Caution Below

Photo Diode Monitor Output (-1 V/mA)

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

No Connection (Leave This Pin Floating)

-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

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