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I am curious if someone could explain what will happen if you were to "cap" or limit the voltage with rising current through a laser diode. Let me explain why I ask this a little more and then maybe my question will make better sense. When testing a diode I have seen several members here use a power source that regulates both voltage and current. On some of the testing it appears all that is being adjusted is the current (I.e. Upwards) and at higher currents the voltage starts to rise. It doesn't appear that the voltage is being increased by the tester yet the readout shows an increasing voltage. On these tests are they adjusting the voltage upwards or is this readout measuring the voltage change somehow caused by the diode at higher currents? Or another way of saying this is, does the voltage drop across a laser diode increase at higher currents? If so then this is the root of my question. It's based upon an assumption that may be incorrect the assumption I am making from watching these tests is that voltage drop across the diode increases as current increases. If this is the case and voltage drop across a diode does increase at higher currents then what would happen to the process if the voltage were capped somewhere below the typical drop for that current? Another example (remember my assumption could be totally wrong): let's say your testing a 445 diode and at 1a the drop across the diode is 4.5v, and then at 1.2a it rises to 4.6v, then at 1.4a it would rise to 4.8v (I'm using these numbers for demonstration, not saying this is what would be happening on a 445 diode). If this were the case and I regulated the voltage to 4.7v but turned the current up to 1.4a (that may have reflected a 4.8v drop) what would happen?
Again, my assumptions could be totally incorrect but from what I have seen it seems with certain diodes the voltage drop across the diode increases with higher currents. If I am wrong in this assumption then someone please explain why we see the need for higher voltages applied at higher currents.
The whole reason I ask this is to learn if there would be an advantage to regulating the current and voltage across a laser diode. Usually I build my own linear drivers from reverse wired LM3xx series voltage regulators. I could just as easily add voltage regulation before or after the current regulator if there was a derived benefit.
I understand the basics of why we generally use current regulation with LD's, due to their finicky nature to draw more current at higher temps and go into thermal runaway and they are current hungry, that at set voltages they can pass more or less current depending on varying factors. What I am less clear on is how they deal with voltage. Until now I've always thought of them as any other diode that has a characteristic voltage drop across it. Lately I am starting to see that voltage drop across a LD is more dynamic and may change with certain other variables. If this is truly the case then it would seem that regulating both current and voltage might improve stability and reduce potential adverse effects.
Really interested to see what someone has to say about this. Thanks agin for your assistance in advance.
Again, my assumptions could be totally incorrect but from what I have seen it seems with certain diodes the voltage drop across the diode increases with higher currents. If I am wrong in this assumption then someone please explain why we see the need for higher voltages applied at higher currents.
The whole reason I ask this is to learn if there would be an advantage to regulating the current and voltage across a laser diode. Usually I build my own linear drivers from reverse wired LM3xx series voltage regulators. I could just as easily add voltage regulation before or after the current regulator if there was a derived benefit.
I understand the basics of why we generally use current regulation with LD's, due to their finicky nature to draw more current at higher temps and go into thermal runaway and they are current hungry, that at set voltages they can pass more or less current depending on varying factors. What I am less clear on is how they deal with voltage. Until now I've always thought of them as any other diode that has a characteristic voltage drop across it. Lately I am starting to see that voltage drop across a LD is more dynamic and may change with certain other variables. If this is truly the case then it would seem that regulating both current and voltage might improve stability and reduce potential adverse effects.
Really interested to see what someone has to say about this. Thanks agin for your assistance in advance.