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# Circuit causing low wattage with GB LD?

#### misoup

##### New member
Well, it's my first post after lurking here for a while, so why not start with a question?

Would there be a formula to calculate the wattage of the output of a LD by knowing the voltage and current?
Simple P=IV doesn't seem to work (or am I just doing the math wrong?).

I have a modified (ok, practically changed until it doesn't resemble) Daedal's circuit. Basically, I have a LM317, 10 ohm resistor and 2 silicon diodes in series connected to a cap and LD in parallel. I measure the voltage to be around 2.1, and the current at 200 mA. I can't burn a match, or else I haven't held it there long enough. When I short out one of the diodes with a wire, I get 2.3 V at 250 mA. Yeah, I put it at a really dangerous current, but the voltage seems really low. I can burn a match with the laser after a few seconds, but I'd rather have a long living LD since it's going to be my only one for a while.

So, is the low voltage affected my output? If so, how could I fix that? The circuit is still bare, so I can desolder and resolder some different components if needed.

Sorry, if this is a really stupid question, but I really don't know electronics well. I actually learned more about electronics messing around with the circuit than in my whole life. Anyway, thanks especially to Senkat who supplied this diode

#### chimo

##### New member
Something doesn't add up. If you have a 10 ohm resistor as the sense resistor, then your maximum current should be 125mA. Can you draw a pic of how you have it assembled.

On the wattage question, you have to differentiate between electrical input and light output. There is a conversion loss in the LD. The only real way to know is to do actual measurements.

misoup said:
Well, it's my first post after lurking here for a while, so why not start with a question?

Would there be a formula to calculate the wattage of the output of a LD by knowing the voltage and current?
Simple P=IV doesn't seem to work (or am I just doing the math wrong?).

I have a modified (ok, practically changed until it doesn't resemble) Daedal's circuit. Basically, I have a LM317, 10 ohm resistor and 2 silicon diodes in series connected to a cap and LD in parallel. I measure the voltage to be around 2.1, and the current at 200 mA. I can't burn a match, or else I haven't held it there long enough. When I short out one of the diodes with a wire, I get 2.3 V at 250 mA.  Yeah, I put it at a really dangerous current, but the voltage seems really low. I can burn a match with the laser after a few seconds, but I'd rather have a long living LD since it's going to be my only one for a while.

So, is the low voltage affected my output? If so, how could I fix that? The circuit is still bare, so I can desolder and resolder some different components if needed.

Sorry, if this is a really stupid question, but I really don't know electronics well. I actually learned more about electronics messing around with the circuit than in my whole life. Anyway, thanks   especially to Senkat who supplied this diode