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# Help making a test load for a diode laser

#### Macoleco

##### New member
Hi,

I am working on a current and temperature controller for low power diode lasers (<200 mA), and I need to make a test load to simulate them. I found some information and it seems the general idea is to use a resistor of known value (like 1 Ohm), and some diodes. Then you measure the voltage and calculate the current. My question is, how many diodes and what kind of diodes do I use? All the samples I find use different diodes and different quantities.

Thank you.

#### diachi

##### Well-known member
Hi,

I am working on a current and temperature controller for low power diode lasers (<200 mA), and I need to make a test load to simulate them. I found some information and it seems the general idea is to use a resistor of known value (like 1 Ohm), and some diodes. Then you measure the voltage and calculate the current. My question is, how many diodes and what kind of diodes do I use? All the samples I find use different diodes and different quantities.

Thank you.

Regular silicon rectifier diodes work fine. Number required depends on what the Vf of your laser diodes is and what current you are using. Check the rectifier diode datasheet to find the voltage drop of the diode at your operating current, then figure out how many diodes you need to have a roughly equal voltage drop to your laser diode.

#### paul1598419

##### Well-known member
If you are using a 1 ohm resistor the voltage drop across it will also factor into the number of rectifiers you will use to approximate the Vf of your laser diode.

#### Macoleco

##### New member
Regular silicon rectifier diodes work fine. Number required depends on what the Vf of your laser diodes is and what current you are using. Check the rectifier diode datasheet to find the voltage drop of the diode at your operating current, then figure out how many diodes you need to have a roughly equal voltage drop to your laser diode.
Thanks for the answer

So if my current driver has a compliance voltage of 3V at 200 mA, then it means that it only works for diode lasers of 3 V or less? Or is the compliance voltage not related to the voltage drop of the diode laser?

Edit: ignore the question. Already found out

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#### paul1598419

##### Well-known member
Just as an average you could assume that most silicon rectifiers drop ~0.7 volts. That is for each rectifier in the series. Add those to the voltage drop across your sense resistor and if it is close to the Vf of your laser diode then you have enough rectifiers in the string.