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Laser Driver FAQ

Frequently Asked Questions-

1.  What does it mean by a “constant current” driver?
2.  Why do I need a constant current driver?  Can’t I just use a lab power supply to hook up my laser diode without a driver?
3. What is “compliance voltage”?
4.  How do I determine which laser driver is the one I need?
5.  Why don’t I just get the laser driver kit with the largest compliance voltage so it will work with every laser diode I have?
6.  I am putting the driver in a small compartment in my system, do I need to provide cooling?
7.  Why are there two kinds of connectors for both the output and the input control signal?
8.  I want to buy 8 drivers for my system.  Can I buy them without the power adapters and hock them  up to my own power supply to run all 8?
9.  I want to use my own power supply to connect the driver.  How do I choose which supply to use?
10.  Can I use a adjustable “lab supply” to provide power to the driver?
11.  I want to connect the driver board to a National Instruments DAQ board.  Can I do this?
12.  I have a system that I want to integrate a driver into that has 24 volt relay switches for turning on the laser.  Will it work with 24 volts?
13.  I need to be able to computer control the driver and turn it on and off in 1 ms intervals.  Can this work?
14.  My system that I want to integrate into only has an output that has reverse logic.  Instead of reprogramming the software to change this, can the driver accept inverted logic?
15.  I sometimes will want to run the driver in CW mode and sometimes in pulsed mode.  Can I do this?
16.  Is there any way to monitor the current output from the board?
17.  I don’t want to purchase on the website, can I call and purchase over the phone?
18.  Do you have a discount for multiple orders?
19.  I need to provide a quotation to my lab supervisor to get purchase approval.  Can you provide one for me?

 

1.  What does it mean by a “constant current” driver?

Constant current drivers provide exactly what it says, a constant current.  The driver will provide exactly the amount of current set at whatever voltage is needed by the laser diode to reach that current.  It will adjust the voltage to keep the same amount of current to the laser diode at all times.

2.  Why do I need a constant current driver?  Can’t I just use a lab power supply to hook up my laser diode without a driver?

You certainly can hook up a lab power supply to a laser diode and provide a voltage and current to the diode, but you will be operating it as a voltage controlled source.  With providing a constant voltage instead of a constant current you have the possibility of having a “run away” situation in which the current will increase and the voltage will stay constant.  If you keep the voltage constant across the diode, then as it heats up the current will increase.  As the current increases, the laser diode will heat up more, which in turn creates more current.  This process, if left on its own will eventually destroy the laser diode.

3.  What is “compliance voltage”?

Compliance voltage is the voltage required across the laser diode to achieve the desired current output.  Across the laser diode, as the voltage increases, the amount of current produced increases.  For a particular current level, there is an associated voltage level that is needed.  This is called the “compliance voltage”.  As the compliance voltage is also associated with a current level, it should always be rated together.  An example is “2.5 Amps @ 3.5 Volts”.  For a laser driver, this means that it can provide up to 2.5 Amps at a voltage of 3.5 volts.

4.  How do I determine which laser driver is the one I need?

First you need to know the voltage and current characteristics of the laser diode you are going to be driving.  For example, an 808nm IR diode will have output current versus voltage for the following graph:

Laser Diode Voltage vs Current Graph

 

So, if you would like to drive the laser to 1.5 amps, then you will need to have a compliance voltage of at least 2.5 volts.

5.  Why don’t I just get the laser driver kit with the largest compliance voltage so it will work with every laser diode I have?

Well, you can do this but you may need to provide extra cooling when using diodes that have low compliance voltage requirements.  As in the previous question, you can see that the output current will remain the same no matter which power adapter you choose.  HOWEVER, and this is a big however, the remaining voltage that is not needed by the laser diode will be dissipated as heat.  So, if you choose to have the 12V adapter and only need to have 2.5V compliance, then the remaining voltage will be dissipated across the regulators as heat and could possibly cause a thermal shutdown.

6.   I am putting the driver in a small compartment in my system, do I need to provide cooling?

Probably not.  Much effort has been put forth to design the laser drivers to be “room temperature” safe for operation even at the maximum levels.  This design assumes that there will be some airflow to the board.  However, if there is not adequate airflow, then there might be a need for extra cooling.  It also depends on if the compliance voltage of your laser is within a couple of volts from the compliance voltage rated by the driver.  If you are not dissipating much extra heat then there might not be a problem.  However, there is the option for a 5V fan that you can purchase in the accessories section that can be connected to the board if needed.

7.  Why are there two kinds of connectors for both the output and the input control signal?

The screw terminals are provided for easy access for prototyping and research applications where you might be changing out the connections many times.  For integrating into systems, the Molex minifit Jr. connectors provide a secure connection that will not come free, even with mechanical movement.

8.  I want to buy 8 drivers for my system.  Can I buy them without the power adapters and hook them  up to my own power supply to run all 8?

Yes.  Purchase the drivers with the OEM package and they will not come with power adapters.  Instead, they will come with a bullet connector with output leads that can be attached to your power supply.  You can choose either the straight or the right angle connector.

9.  I want to use my own power supply to connect the driver.  How do I choose which supply to use?

Make sure that the supply will match the compliance voltage of your laser diode to within a couple of volts and also be able to provide enough current to support the driver.

10.  Can I use a adjustable “lab supply” to provide power to the driver?

Yes, with the OEM version you can connect it to the output of a bench top supply.  Just make sure it can provide enough current for the driver.  You can then adjust the voltage on the supply to reach the maximum current needed to minimize the excess voltage and heat.

11.  I want to connect the driver board to a National Instruments DAQ board.  Can I do this?

Yes.  The input control signal needs just 2.8 volts to turn it on, so it will work with standard DAQ boards provided by NI and most other vendors.

12.  I have a system that I want to integrate a driver into that has 24 volt relay switches for turning on the laser.  Will it work with 24 volts?

Yes.  The maximum input voltage into the isolated input it 36 volts.

13.  I need to be able to computer control the driver and turn it on and off in 1 ms intervals.  Can this work?

Yes.  The maximum rate the driver can be switched without losing signal integrity is 5KHz, or 200 microsecond switching speed.

14.  My system that I want to integrate into only has an output that has reverse logic.  Instead of reprogramming the software to change this, can the driver accept inverted logic?

Done!  We have added a jumper to change the input control signal so that it can invert the incoming signal.  When it is low the driver will turn on, and when it is high it will turn off.

15.  I sometimes will want to run the driver in CW mode and sometimes in pulsed mode.  Can I do this?

Yes.  If you are doing research or a project, you can use the switch on the front to change it to CW mode or Input Control Mode.  If you want to integrate it into a system, keep it always in Input Control Mode and when you want it in CW just give it a logic high signal for as long as you want it on.  When you want to pulse it, then give it a pulsed signal.

16.  Is there any way to monitor the current output from the board?

Yes.  The TP1 and TP2 on the board are for current monitoring.  They are the voltage across the resistors that can be used to determine the current output of the driver.  TP1 is the voltage at the regulator divided by 3.61 and TP2 is the voltage at the output divided by 3.61.  You can take this and divide it by the resistance to get the current at the diode.  It is divided by 3.61 so that it can be input into a standard 3.3V microcontroller.  The instruction manual will have the values of the resistance for the current levels to complete the calculation.

17.  I don’t want to purchase on the website, can I call and purchase over the phone?

Yes.  We except all major credit cards for phone orders.  Your order will be processed and the transaction receipt can be emailed quickly.

18.  Do you have a discount for multiple orders? 

If you call or write our sales team then we can make provisions for giving a discount for multiple orders over 5.

19.  I need to provide a quotation to my lab supervisor to get purchase approval.  Can you provide one for me?

Yes.  We are happy to prepare a quote.  Just give us the details in an email to sales@jtechphotonics.com or give us a call on the phone and we can discuss your needs.

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