Parallel zeners?

[azatplayer]

Possible? What's the relationship? I know you add the volts for series, do they halve in parallel? Power rating the same?

[Cliff Schecht]

Zener's don't parallel well. Since they usually have a 5-10% tolerance, one diode is bound to turn on sooner than the other one and, at least momentarily, conduct all of the current that is supposed to be spread through the multiple parallel devices. If you are trying to get by with using multiple low power Zener's, you will quickly find that this doesn't gel well in practice (meaning one will probably pop quickly and the other one soon after). This effect only gets worse as you parallel more.

[azatplayer]

Thanks Cliff.

[DonMoose]

To further Cliff's answer - diodes don't parallel well regardless of type. If you're simply stuck with having to do it, you have to give each diode its own series resistor (10 ohms is enough).

It's better to hold out for a diode of the ampacity you require - if you need some more sources, there are (in the US)

http://www.digikey.com
http://www.newark.com
http://www.mouser.com

[tubeswell]

On the other hand the PIV adds up if the diodes are in series (as does their power handling capacity, and forward voltage drop)

[niftynev]

You could try a single higher wattage zener instead.

You can get them in 5 watters; they're the same size as a 1N5408.

[martin manning]

On the other hand the PIV adds up if the diodes are in series (as does their power handling capacity, and forward voltage drop)

No, they would all carry the same current so a series string has no more amperage capacity than a single diode.

[tubeswell]

On the other hand the PIV adds up if the diodes are in series (as does their power handling capacity, and forward voltage drop)

No, they would all carry the same current so a series string has no more amperage capacity than a single diode.

I was thinking about zener diodes when I posted this because that was the thread topic. If you put 2 x 5W zeners in series you effectively have the sum of the voltage drop of the zeners at 10W of power handling overall, because each zener handles its own voltage drop at 5W - same sort of thing as putting two 5W resistors in series. I have done this and it holds up.

[martin manning]

OK, got it, and of course (Oops) I was thinking regular diodes rated for current.