Old 10-21-2008, 02:06 PM #1
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Default Meredith ACC diode driver problems

Hi Guys,

I am new to this site, and learning lots from the various threads in this section particularly.

After ordering some meredith instruments collimators, I decided to try the ACC driver kit (LDD-10) to run a PHR-803T diode. This driver requires a 6-9V power supply.
I put the kit together no problem, and by using a multimeter connected to the 'test points' I was able to get the readings stated in the documentation (11-approx 123 mA) with an LED as a test load. My power supply was an alkaline 9V battery. Adjusting the potentiometer brightened and dimmed the test load LED as expected. After this I hooked up the PHR-803T in the meredith collimator and the unit lased well. Attaching the multimeter showed the same range, but I tuned it down to approx 90mA. After a few more times of turning the laser on and off, I noticed that the potentiometer would only adjust from about 11-60mA. The diode stopped working not long after.

Thinking I may have stuffed up the driver I construced another one (I had ordered 2). I tested this one and got the same mA readings as for the first one. I noticed the same phenomenon regarding the pot range changing. Another PHR-803T and I was ready to try again.

After searching the website (and indeed the web) regarding the PHR-803T and the meredith driver I came across some posts from Marks47 in the thread

laserpointerforums.com/forums/YaBB.pl?num=1189562336;start=all

"Don't feel bad. I just killed my third one. It's just a glorified LED now.
I have found out the HARD WAY and BLOWN A THIRD (#*&$ing DIODE that VOLTAGE MATTERS no matter WHAT anyone on these forums says.
Forget the load/no-load BS, do NOT run the Meredith instruments regulator on a nine volt battery unless you plan on putting a resistor in parallel to suck off some of the voltage!!!!
I'm sorry. I know this will not be a popular thing to do, but since these BR diode discussions are scattered across at least 2-3 threads, I'm repeating the post there, too."


After reading this I decided to try a lower voltage, so I tried 4x AA alkaline cells (which gave 6.3V). The unit lased well, but the pot adjustment would only go to 35mA and the beam looked significantly dimmer. After about 1-2 min the spot dimmed right down, and the shape changed to rectangular. I am assuming that this is optical damage to the diode.
The unit still lases, but is nothing like it used to be.

Now I was told by the folks at Meredith that this unit was suitable for a PHR-803T, and unless I have made a mistake somewhere (which is possible), the meredith driver unit does seem to wreck these diodes, which Marks47 asserted was the case with a 9V battery.

Can anyone shed any light something I may have done wrong?
Does anyone else have any experience with this driver/diode combination?

I have ordered some rockstar drivers for my next attempt, but I still want to know what went wrong here, as I would hate to make the same mistake and ruin more diodes.

Any suggestions would be greatly appreciated.



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Old 10-21-2008, 04:02 PM #2
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Default Re: Meredith ACC diode driver problems

The driver is a basic current regulator driver, the input voltage needs to be 3 volts higher than output voltage under load in order to regulate the output current.

803T Diode needs over 5v @100mA, make sure your 9v battery reads over 8.5v under load.
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