PL450B single mode build problems

I am trying to get a PL450B single mode build happening. I am using a Microboost. did the usual things: set my dummy load to 8 diodes (~6V drop), connected the driver to the load and battery (18650). measured the current on the load (1ohm) and set it to 350mA. of course solder blobbed the driver to the right current range. shorted out the driver LD output. connected to the LD and I get 10mW or so out of it.

So, I got a new diode and a new driver suspecting either or both. did the same thing, same result.

As a test I connected my meter in series with the LD in mA mode and got the same 350mA when the LD was operating. measure the V on the LD and it was 6.5V.

What the heck. I must be missing something for a completely new driver and LD to do the same thing the first set did. also ensured the battery was full at 4.1V. its a panasonic 3400mA 18650 almost new.

any pointers?

I am pretty sure you have to measure the voltage across the test load and not the current, where 1 mv = 1 ma.
Maybe that's the problem setting the current?

yes. when i measure the "current" on the test load I am using volts on the meter across the 1 ohm resistor and setting it 0.350V which corresponds to 350mA.

Hey I just took a look at the datasheet for that diode and it says the max operating current is 165ma. Some of the osram diodes decrease power when given too much current, so I'd try turning the current down to see if that fixes it.

Please can you hook your micro-boost up to a bench supply and set it for 3.5 volts out and see if it works then.

Thanks for your suggestions, guys. The reason this is confusing me is that I have a single mode laser I got from Lazerer that is outputting about 280mW and I actually built my own labby using a PL450B and a labby driver that is also doing 280mW. I am pretty sure I set it at 350mA.

I decided I wanted to build a pointer in an SH032 host. So I set the driver to 350mA and expected the same result. The LD lases but its dim. I suppose 350mA is pushing it too hard.

I don't have a bench supply so its hard to diagnose. However last night I bought one and its on route to me. Your point is well taken Flaminpyro. I have tried to do without the bench supply all this time but really if you are doing builds its a necessary tool. Same with your diode presses - I tried to do without but really, they are necessary. I could have paid for a full set of presses and removal tools with the couple of LD's I've damaged trying to do without (in otherwords I suggest anyone doing builds to buy the necessary presses - consider it insurance and if the build works out, then you have a nice new tool to use in the future).

So I am going to put these builds on hold until I get the bench supply so I can better diagnose whats going on.

Correct me if I am wrong, but the first thing I would do is put the LD on the bench supply and slowly turn up the current to find out the specific LD's max operating current. Then power the driver from the bench supply and set the driver current appropriately. The bench supply will also be useful to test other LD's and drivers i have sitting around that I am unsure of.

Time to put on big boy pants.

On a bench you want to find the typical voltage of the diode and set the voltage just under that and the current to zero. Then power off short the leads, connect the diode and power on. Slowly turn up the current. If you need more voltage overhead you can repeat the process with a little high voltage but usually if just doing a life test on a power supply staying under the nominal voltage of the diode will reduce the capability of a surge in the supply from harming the diode.

Also when you say you put a DMM in series with the output of the diode be careful I have seen this method LED many diodes. Suggest solid, securely soldered connection only between the diode and driver as a microsecond of intermittent contact will chage the cap and spike the diode. Also when you say you connected the diode was it a soldered secured connection or maybe clips or some other non soldered connection?

While there is not much benefit from going form 300mA to 350mA it takes 2 times or more that in current to LED or pop these didoes. They are some tough little bastards. I usually set them 200mA-300mA for the best part of the efficiency curve.:beer:

Thanks DTR. Once I get the bench supply I will better be able to diagnose the problem(s).

I didnt run the diode off clips except when measuring the in-circuit current. Then I used clips (good ones) but I get your point. The problems existed before that and were consistent after that too. so hopefully that didn't damage anything. we'll see once i get the supply and further diagnose. I didn't realize 350mA was pushing it too hard. If I blew the LD I'll get another and try again.

does that diode pull 6 volts?

nkgamer1990 said:

does that diode pull 6 volts?

Click to expand...

Apparently. Look at the reading on the PSU

http://laserpointerforums.com/f65/osram-pl450-450nm-80mw-power-chart-71645.html#post1031770