Flexdrive failure?

[Morgan]

Hi All,

I've been asked to repair, (well install a new LCC!), but I'm concerned about the health of the driver. It's the well known Flexdrive, (version 5, I'm pretty sure). A nice compact little boost driver. The problem is that, as anyone who's used these will tell you, they do not like being run without a load. This is what happened to this poor beastie but how to tell if it's damaged?

The first thing I did was attach my test load and take a mV reading. All seemed ok at 380mV indicating 380mA output. So I went ahead and hooked up an LCC, (GGW-H20L red), that had previously seen some mild action and it was immediately turned into an LED. I did ignore the high pitched whining coming from the Flexdrive as the output seemed normal but after another fresh diode went the same way I'm concerned the original broken contact between diode and driver has done for it. This is a battery build I'm afraid, (some may know what that means! Yukk! Normal lines of communication seem to be out at the moment else I would have asked elsewhere, sorry!), but the battery is fully charged, (well almost - 4.1V), and happily runs other similar setups.

Can anyone help to pin down what's going on here? Although I've worked with these drivers before, and I must say quite like them, I haven't yet experienced a failure so don't know what I'm looking at here. I'm loathed to just replace the driver until I can be certain of its demise. Any help is much appreciated.

M


P.S. Must log out now until tomorrow but I will be back then with thanks for input...

[drlava]

Hi, the FlexDrive is the micro portable laser driver for battery operated units, most often used over at LaserPointerForums. As such, you'll get the best response over there.

A few things to note:

Running the V4/5 without a load can damage it, as it will run the driver out-of spec. Typically damage can be seen only after a period of time of running without a load, not a brief instant. However due to slight manufacturing variability, it's possible that damage can occur faster with some units. One thing to keep in mind is to always connect the laser diode and power input leads with a good solder joint that fills the through-holes on the PCB. If you don't do this and your diode temporarily becomes disconnected and then reconnected, the output capacitors will charge then discharge through the diode with likely harmful effect.

There should not be a high pitched noise coming from the driver during normal operation. The switching frequency is well above the audible range. Looking over at LPF, this particular thread stands out regards to high pitched noise:
the thread

with this helpful comment:

I have had this problem before with 3 different drivers.
One squealed because of a bad battery supply.
One squealed because of a cold solder joint at the + input.
One squealed because the momentary switch did not make good contact.

I have never received a defective driver from Dr.Lava. In all 3 cases of malfunction, it was user error or bad components in the setup... and every time it was fixed with a little troubleshooting.

So, check into those but if they are not the cause, suspect the driver has been damaged.

[Morgan]

Hi Dr-Lava,

Thanks for the reply. (I did PM you over at LPF but there's been some downtime over there and needed some info to pass on. I had seen the drivers mentioned over here so thought I'd ask... )

I'll check out the post you linked to and see if that resolves the problem.

I did get the driver on a scope today but I'll take this one back to, "... the place that shall remain nameless'"

Just to clarify... any potential failure here has been due to post installation error, (not mine), and is not a fault of manufacture or design.

Thanks again,

M