Where to buy transien voltage suppressor TVS?

[MikePL]

So all I know is that TVS is used to protect the LED from current spikes. Every TVS has a maximum voltage which it allows to pass, everything above it is blocked.

TVS diodes are usually used in automotive applications (lots of spikes). The TVS is connected between both legs of the LED and that's it.

My question is where can I buy TVS diodes over the internet. Both 'normal' and SMD. I can't find any. Well I've found one shop but they want $0.4 for a piece, which I find oddly expensive, given the situation that I will need quite a few. Other shops have terrible shipping costs, like $10 for stuff that easily fits in an envelope. I would like to know if there's a nice shop like DealExtreme (free shipping) where I can buy.

My second question is how to connect the TVS to a power LED (3W). My logic tells me to do it before the driver. Or maybe there are already some safety features built in the LED drivers?

 

[James Jackson]

Both Digikey (http://www.digikey.com/) and Mouser (http://www.mouser.com/) have these.

They also have price breaks for quantities, and both SMT and through hole versions of the TVS devices.

Placement of the TVS should be where the power comes into the driver. Be sure to use heavy traces - as well as a fuse on the plus line. The reason? If memory serves correctly - one mode of failure of the TVS devices (yes, they eventually fail) is a dead short. If the traces that you have on your printed circuit board are not large enough to handle the current until the fuse blows, they will act as a fuse - melting the copper traces and going open-circuit (permanently). (It's messy - I know.)

Good Luck - and great idea.

Regards,

James Jackson
Oztronics

 

[AzN1337c0d3r]

What are you planning to do with your LED that needs TVS circuitry?

Couldn't a simple capacitor across the legs of your LED suffice?

 

[MikePL]

I am planning automotive use. Interior lamps mainly and also taillights. Cars have spikes up to 40V due to a lot of components that switch on and off, like relays. There's also a lot of 'noise' from the ignition coils and other stuff maybe. If a capacitor is enough to smoothen the current before the LED driver, then I would obviously like to go that route.

But the question is if a capacitor is enough?
Or maybe the driver already can handle spikes by itself?

If the answers to the above questions are 'no', then I would like some help with the TVS. The problem is that I can't find the right component. I need a TVS with a maximum voltage of 15V (anything above that is cut) and capable of handling 12W (I won't connect more than 3 LEDs per driver).
When I looked at the websites mentioned above, I couldn't find the right element. Either I got 10,000 results or a few results where I had to order a minimum of 30,000 units or I got no results at all. Hmmmmm.....

 

[Calina]

Maybe you would find more info if you looked in the automotive forum as this has probably been asked before:
http://www.candlepowerforums.com/vb/forumdisplay.php?f=87

 

[AzN1337c0d3r]

Depends on how long these transients are...

Another thing to look into may be a zener diode in parallel with the LED?

 

[MikePL]

Calina,

dayyymn, I didn't even know such a sub-forum existed. Thanks for the link but I will wait here what happens. After all this is a LED specific problem here and not only automotive. Spikes are not only in cars.

AzN1337c0d3r,
What a nice and easy to remember username you have. When I start planning a second child, I will take this name into consideration, LOL
Could you elaborate on the length of the transients a little bit? Why does length matter?

 

[AzN1337c0d3r]

Calina,

dayyymn, I didn't even know such a sub-forum existed. Thanks for the link but I will wait here what happens. After all this is a LED specific problem here and not only automotive. Spikes are not only in cars.

AzN1337c0d3r,
What a nice and easy to remember username you have. When I start planning a second child, I will take this name into consideration, LOL
Could you elaborate on the length of the transients a little bit? Why does length matter?

So you can know what size capacitor to spec to absorb those transients? Obviously if the transients are long and sustained, you would need a huge capacitor, which would make it impractical.

As for a TVS/Zener diode, Digikey might have what you're looking for?

http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=1377034;keywords=zener diode

 

[mzzj]

As for a TVS/Zener diode, Digikey might have what you're looking for?

http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=1377034;keywords=zener diode

Better yet:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=655429;keywords=tvs

Mikepl, we would need to know which driver you are using too be able to tell if its protected or not.

Automotive power supply is _really_ nasty, infrequent spikes of +-120v with enough current to blow up smaller TVS diodes to pieces. Google for "load dump" or check this:
www.onsemi.com/site/pdf/PET_Nov_04_Zener_Diode_Paper.pdf

 

[Calina]

There is something I don't understand. Cars are already running a lot of sensitive electronis like radios, CD players, GPS and more. There must be some protection built in for these.

Is it not possible to connects the LEDs into those already protected circuits?

 

[AzN1337c0d3r]

There is something I don't understand. Cars are already running a lot of sensitive electronis like radios, CD players, GPS and more. There must be some protection built in for these.

Is it not possible to connects the LEDs into those already protected circuits?

These usually have a nice filtered power supply for converting the power down to the level the electronic needs of that particular device. One of the primary goals of a power supply stage is to filter out noise (such as what you would find inside a car). Unfortunately these power supplies are built into the devices themselves and opening them would void your warranty. Even if you didn't care about voiding the warranty, it usually is a hassle to route the power from inside the device (gotta open them up, solder in a couple of wires, drill some holes in the casing to let the wires out, etc etc)

I wonder however, if you could look into taking power from the circuit that powers your car's ECU. I'll bet that's really clean, since it's a microprocessor that has to function with a high degree of reliability. But then again, might not be the best idea, seeing as you're messing with the ECU of your car, which means if you screw anything up, well 1) It's going to be expensive to replace and 2) you really don't want your car to randomly malfunction in the middle of an intersection, etc.