Need help diagnosing a driver issue

Hey all,
I just need your help for a while on finding the cause of a problem I had.
When I was working on this red ~250mW labby I ended up blowing up a previous laser diode. The post shows the replaced diode.

I had harvested the diode from a DVD burner and was driving it fine with an LM317 DDL Driver at 250mA. These DVD diodes are usually driven at higher current, however I wanted mine to last and not get too hot. (measured 240mA on a multimeter)

Everything was fine. I was running the DDL driver from a 6V power supply. I then wanted to put it onto my 12V wall-wart transformer (outputs DC) for a more "permanent" setup. I connected it up, and nothing happened. The laser was off.
I switched it back to the original power supply, and the laser had gone LED. It was very dim and was still drawing 240mA.

I measured the voltage of my "12V" transformer and it measured at 17.5V. This is probably the source of the issue.

I ended up "solving" the problem by using a new diode, and using a second LM317 limiting the voltage down to 6V for the DDL driver, plus it smoothens out the voltage. I want to know what the actual problem was.

I thought constant-current devices did not have an exact voltage requirement. Do you think the 17.5V would fry the diode, even though it was at 240mA, and also is the 1.25V reference voltage theoretically subtracted from the input voltage in current regulation mode (eg. 5V in = 3.75V out with limited current), and what is the 'safe voltage range' with a DDL driver?

Thanks for your time and I hope you send a reply I should have connected the test load when connecting the "12V" transformer

Did you use a rectifier? If not, It blew up because the transformer outputs AC not DC. You should make a rectifier to convert AC to DC. You might also want to supply a voltage of only around 5 volts to minimize ohmic losses on the driver.

Obviously, The diode can't handle 17.5v.

Zeebit said:

Did you use a rectifier? If not, It blew up because the transformer outputs AC not DC. You should make a rectifier to convert AC to DC. You might also want to supply a voltage of only around 5 volts to minimize ohmic losses on the driver.

Click to expand...

Oops, forgot to mention that it's a standard wall wart power adapter,
it has a bridge rectifier built in.
And would a LM7805 voltage regulator work fine next time (outputs 5V)

My guess is you zapped it with ESD, or forgot to discharge the capacitors before connecting it to the diode. Also keep in mind the LM317 will get substantially hotter at 17V than 6V, so you might need heatsinking on it.

Things said:

My guess is you zapped it with ESD, or forgot to discharge the capacitors before connecting it to the diode. Also keep in mind the LM317 will get substantially hotter at 17V than 6V, so you might need heatsinking on it.

Click to expand...

I had discharged the caps (even shorted out the caps inside the wall-wart transformer) so I don't think that's an issue (well I didn't ground myself ). About the heatsinking, I fixed that in the final version, the link to it is in the original post, in blue.