GO POUND GROUND ...

ABOUT TEST LOADS IN CONSTANT

CURRENT MODE

Using Constant Current when setting up the test load

allows you to set the Current Limit and Current Setpoint.

Wavelength trimpots are 12-turn trimpots and are turned

counter clockwise (CCW) for off and clockwise (CW) for on,

the exception being the LDTC 2/2 E & O, where they are

reversed. Consult the product documentation to verify the

direction before proceeding.

NOTE:

The 12-turn trimpots continue to turn after the 12th

turn has been reached. Any additional turns do not vary the

resistance.

13

13

13

Figure 1. Example Test Loads for a Laser Diode in

Constant Current Mode

SET UP THE LASER DIODE TEST LOAD

USING CONSTANT CURRENT MODE

1. Attach a test load between the Laser Diode Anode (LDA)

and Laser Diode Cathode (LDC) of the laser diode driver

(see Figure 1).

2. Set the driver in Constant Current mode.

3. Connect the multimeter, in voltage mode, between the

Current Monitor (I

MON) and common Ground (GND) pins.

4. Turn the Current Limit trimpot fully off, usually 12 full

rotations counterclockwise (CCW).

5. Turn the Current Setpoint trimpot fully on, usually 12 full

rotations clockwise (CW).

6. Attach a 5 V power supply. A higher voltage power

supply can overheat the controller when using test loads.

7. Enable the unit.

8. Use the transfer function calculation in the datasheet to

determine the I

MON reading at the desired current limit.

9. Increase the Current Limit by turning the trimpot, usually

CW, until the desired maximum I

MON limit voltage is

reached and then stop. The Current Limit is now set.

10.Use the transfer function to calculate the I

MON voltage at

the desired operating current.

11. Decrease the Current Setpoint by turning the trimpot,

usually CCW, until the current starts to go down and the

I

MON voltage value is reached.

12.OPTIONAL: Wire a signal generator to the analog

modulation input. The datasheet has the transfer

function equations.

13.OPTIONAL: Replace the multimeter across the I

MON and

GND with an oscilloscope to monitor the output current

variation with time.

14.Once the test load limits have been set and you are

familiar with the system, return the Current Setpoint and

Current Limit trimpots to their respective OFF positions

(usually 12 turns CCW).

NOTE:

If testing a load in Constant Power mode, do

NOT follow this step.

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Application Note AN-LDTC04 Rev. A

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