AN-LDTC04 WAVELENGTH | Alldatasheet
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January, 2014 Page 1 © 2014 • Sales & Technical Support: (406) 587-4910 • Sales@teamWavelength.com • www.teamWavelength.com Using a test load veri fi es that the rest of the equipment is set up correctly and in working order prior to attaching the laser diode. It also allows you to become familiar with trimpot rotation and sensitivity, to correctly set up wiring and monitoring, and to troubleshoot any problems that may arise. The test load processes that follow verify the current output in Constant Current mode and the limits are set up and can be monitored. When setting limits, you are able to see when the limits are reached and can adjust the set up of the controller accordingly. In Constant Power mode, the test load allows you to set up and monitor the simulated photodiode current. The following equipment is necessary when setting up a test load:
- Laser diode driver or driver with evaluation board
- Multimeter, set to read voltage
- Oscilloscope (optional, needed only if testing analog modulation input)
- Signal generator (optional, needed only if testing analog modulation input)
- Test load, for examples see Figure 1 for Constant Current and Figure 2 and Figure 3 for Constant Power
- 5 V Power supply
- Connection cables or wires TABLE OF CONTENTS Why Use a Test Load for Laser Diode Set Up? page 1 About Test Loads in Constant Current page 2 Set Up a Test Load in Constant Current Mode page 2 About Test Loads in Constant Power page 3 Set Up a Test Load in Constant Power Mode page 3 About Temperature Controllers and Test Loads page 4 Set Up a Temperature Controller & Test Load page 4 INTRODUCTION What is a test load and why do I need to use one? How and when should I use one, and how do I know it’s working? These are questions our technical support staff are asked regularly, along with how to set up a test load and which load is best for each Wavelength product series. This Application Note will cover that information, as well as what equipment you need, when to use Constant Current or Constant Power modes, and how to prepare your equipment for the actual load. For the purposes of this paper, we will address using test loads with only temperature controllers and laser diode drivers. A test load is a tool for testing a device or system and measuring a response without using the application load and, ideally, the test load should closely mimic the eventual load. Using a test load is a good way to get familiar with a controller, test how it works, and make sure it operates as expected before the fi nal set up. For example, laser diodes can be expensive and are usually not readily available, so destroying one during set up can be both costly and time consuming. To avoid this hazard, the system can be set up with a test load and tried before attaching the laser diode. A test load can also help show, through monitoring, what happens when limits are exceeded. Additionally, if you are having a problem while using a system, a test load can help troubleshoot any problems. NOTE: While this Application Note will address questions particular to using a test load, it is not meant to replace the product datasheets, which contain all of the equipment, instructions, calculations, and troubleshooting information needed to successfully use the products. WHY USE A TEST LOAD FOR LASER DIODE SET UP?
allows you to set the Current Limit and Current Setpoint. direction before proceeding. Figure 1. Example Test Loads for a Laser Diode in
- Attach a test load between the Laser Diode Anode (LDA)
- Set the driver in Constant Current mode.
- Connect the multimeter, in voltage mode, between the
MON) and common Ground (GND) pins.
- Turn the Current Limit trimpot fully off, usually 12 full
rotations counterclockwise (CCW).
- Turn the Current Setpoint trimpot fully on, usually 12 full
- Attach a 5 V power supply. A higher voltage power
supply can overheat the controller when using test loads.
- Use the transfer function calculation in the datasheet to
MON reading at the desired current limit.
- Increase the Current Limit by turning the trimpot, usually
reached and then stop. The Current Limit is now set.
- Use the transfer function to calculate the IMON voltage at
the desired operating current.
- Decrease the Current Setpoint by turning the trimpot,
MON voltage value is reached.
- OPTIONAL: Wire a signal generator to the analog
- OPTIONAL: Replace the multimeter across the I
- Once the test load limits have been set and you are
whether the sensor feedback is working properly.
- Thermoelectric controller
- 2 Multimeters, one set for voltage and one for current
- 5 V Power supply
- Connection cables or wires
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Figure 4. Thermistor Test Load Figure 5. Simulated Thermoelectric Test Load
- Attach a 10 k Ω resistor in place of the thermistor (see
Figure 4) with a default sensor bias current of 100 μA.
- Connect an ammeter in series with the test load resistor
terminal of the meter must attach to the test load resistor. Make sure the ammeter capacity exceeds 1 A.
- Attach the voltmeter across ACT T and GND.
- Attach a 5 V power supply to the unit. A higher voltage
- Turn limit trimpots to OFF (usually 12 turns CCW).
- Turn the SET T voltage to 1.35 V for cooling and turn
the Current Limit trimpot until the ammeter reads 1 A.
- Turn the SET T voltage to 0.8 V for heating and turn
the Current Limit trimpot until the ammeter reads 1 A.
- When the testing is complete, return the Current Limit
trimpot to the OFF position (usually 12 turns CCW). when setting up the application load. available to help with any questions you may have.
GO POUND GROUND ... REV A
REVISION HISTORY
test load, testing a device, troubleshooting a temperature control system, troubleshooting a laser diode control system, verify equipment set up, © 2014 • Sales & Technical Support: (406) 587-4910 • email: Sales@teamWavelength.com • web: www.teamWavelength.com Page 5