Hobby Laser Pointer | How To Test Laser Driver Current with a Test Load
Always check your laser driver current with a test/dummy load before soldering your diode in to the circuit.


Posted by 94Z28 in Laser How-To

How To Test Laser Driver Current with Test Load

Here is my quick, short and sweet write up about testing your laser or LED driver with a test/dummy load circuit before installing the business end to the driver. I will start off by telling you that this is one of the most important steps to take during your builds; If the driver dealer/manufacturer set your driver to a specific current before shipping it could have magically changed during shipping, or even have a different current because your input voltage may be different than what he set the current at. Bottom line of this paragraph test your laser driver current with a test load before installing the Laser Diode!

You have a few options for test/dummy loads and they range from a fancy “adjustable drop/selectable” test load down to a home-made DIY test load with a few rectifier diodes and a 1 ohm resistor from radio shack.


Survival Laser “Selectable” Test Load


“MADE IN USA. The 3 amp selectable test load may be used to test a diode driver for proper current output and waveform before being attached to an LED or laser diode.┬áThe test load simulates the voltage drop (Vf) of a diode at a given current (A). Voltage drops of 1.4 to 8.5 volts may be achieved using a jumper setting of 2 to 10 diodes. This range is sufficient to cover all normally used optical diodes. Note: This product is fully assembled, not a kit.

The selectable test load is shown in the photos in a suggested setup with a digital oscilloscope (optional).”


You can find a “datasheet” and some instructions for choosing how many diodes at this link, it’s pretty self explained and this one is my favorite choice.

DIY Test Load (I’m on a Budget Edition)

So if you are like many of us hobbyists then you are on a short budget (and could use a lottery win) and you want to do this quick and cheap to get your awesome laser to fire up! First thing you want to do is take a drive to your local radio shack and find these items

  • Pack of 5 or more 1N5404 diodes (If these are out of stock, get 1N4001 TO 1N4004 as sometimes my local shop is out)
  • 1 Ohm 10w resistor (Usually come in packs of 2 and I always get the concrete-sink ones because these get hot)
  • OPTIONAL/AS NEEDED: PCB Board (Small), Header Pins (Positive and Negative Quick-Connects), anything else you may want to dress up.

As you may imagine, you don’t need anything outside of the diodes and the resistor if you don’t wish and this will make it very cost effective (5$ maybe…) Take all your parts home, and solder up the needed diodes for the build you are working on. If you are unsure how many you may need then simply go over to LaserPointerForums and perform a search for those out of the ordinary builds! Make sure you solder your diodes in the proper direction, and the resistor can go at the front or rear of the circuit. You wire up your leads (with power following the diode direct, and ground on opposite end) and check the voltage over the 1 ohm resistor for a 1mv-1ma conversion! Remember anything over 1.0A will begin to get scorching hot fairly quickly so do your tests, and shut the power off!

Here are some images for your reference, if you have any questions about this feel free to comment or contact me I will be glad to help!



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