TEC issue

[Pitts]

Hi guys..

Can I please pick your brains..

I have TEC issue.. I haven't worked much with TECs so my question may seem elementary.

What is happening is, every time I connect my laser up one of the four MOSFET's driving the TEC goes bang.

As the LD module has some very expensive toys inside (like eight red diodes) I have done all my testing with that disconnected.

By a process of elimination and finally a check of the LD module itself (with LD's shorted to avoid static) I find the TEC "negative" (relative term here due H bridge drive) black wire is shorted to the LD module outer chasis.
The inner LD chasis is nicely insulated from the outer housing as are the diodes from it and there is no connection between that and ground.
Very nicely engineered unit.

Now it is driven with an H bridge and of course the MOSfet pairs drive each side.
I would have thought that neither side should be at chassis ground because as soon as you mount it or connect ILDA pin25 you are going to cause smoke ( I have proven this, I own more dead 9530 fets than you can shake a stick at)

Should I expect to see one side of a TEC hard to ground ??
I looked up some sites and they indicate that there is ceramic on both sides ?? I presume therefore it is insulated from ground electrically.

Now before anyone asks, the manufacturer has been very good at trying to help its just that they are out of time phase with down here and busy so each email is taking a few days to get a reply to.
To my suprise they even sent me the schematic. (which I would love to share but can't for obvious reasons... so please don't ask)

I have so far resisted the temptation to remove the inner insulated LD mount to look at the TEC as this is new territory for me.

The LD's are fine.

By the way there are no "warning you must insulate module" stickers on the LD module. Nor are there any warnings on the data sheets provided.
They openly talk about "ground" like this is normal "ground" (chasis) so I assume I have located the source of the short just don't know why yet.

Any thoughts on this ??

Many thanks

Ray
NZ

[dave]

Hi Ray,

If the TEC is being driven with a H bridge, both TEC inputs need to be floating in relation to ground.

Sounds like the high side mosfet is not liking a short circuit....

Perhaps the shorted TEC wire is being pinched between the aluminum chassis and something somewhere along its travels?

[Pitts]

Thanks Dave Thats pretty well where I got to as well.

I guess I am nervous about taking that pretty LD assembly apart to see.

I think it is under the clamp plate somewhere as I can trace all of the exposed wires OK and there are no visible shorts or stray wires, everything is nocely heatshrunk and tidy.

May just have to take the plunge. Hopefully they will come back to me tonight our time.

Thanks

Ray