Zeners in series

Yes, as long as you don't exceed the curent either diode is rated for. If you do, that diode will overheat and short.

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While at it 2 diacs in series , assuming 2x 8V ones , would give 8V ? What if high ohm balancing R across each, too high to turn on the associated device?

Basically, yes. I do it all the time. Doesn't usually work out *quite* right, but close enough as not to normally matter.

Arfa

with

of

And to adjust for the odd 1/4 or 1/2 a volt more, add a normal diode or 2 in the chain

Quite

Arfa

On 10/28/2010 10:10 PM Steve Kraus spake thus:

Done all the time (2 or more diodes in series). You can even take intermediate voltages from taps in a series string of zeners.

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Just one more thing to add. In general the forward drop is a "don't care", however, in some applications, it might enter into the equation, so you have to double that.

On 10/29/2010 11:21 AM Art Todesco spake thus:

It's still the usual 0.7 V per junction, right?

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The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.

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and you can tweak the overall tempco by selection of the elements to combine.

who where wrote in news: snipped-for-privacy@4ax.com:

Don't forward-biased silicon diodes have a tempco reverse that of a zener diode? If I want a temperature-compensated 40VDC, I could combine a 39 volt zener and a diode or two and get very close to

40 volts with minimum drift.

--Damon

There's a natural "turnover point" at something about 5.6 volts for reverse-biased diode junctions. For breakovers below that voltage, the Zener effect predominates, and the devices exhibit a negative tempco. Above it, the avalanche effect becomes predominant, with a positive tempco. Right around 5.6 volts, the tempco can be very near to zero. You can make composite devices with very low tempco for voltages well above

5.6 devices by putting one (or more) of each type in series.

So if you wanted, say, a 40volt stable reference, you'd probably get best performance by putting (say) a 36 volt device and a 4 volt device in series -- or maybe 37 volts and 3 volts; check the tempco curves. And be sure to thermally connect the two devices together.

Isaac

isw wrote in news:isw-F4887F.00161102112010@[216.168.3.50]:

Aha! I'd wondered why that trick wasn't used more often in an integrated package. Thanks for the explanation.

--Damon

While we're talking about stable references, the way to get a low-voltage one (2 volts, say), is to thermally tie together 20 volt and

22 volt devices and take the difference between them as the reference. The two devices (Which should be from the same manufacturer, etc.) will drift together, leaving a constant difference.

Or, you could just use an LM-10...

Isaac

I did this in a VCR switch mode power supply which had failed. I was repairing on the cheap using parts I had laying around. Couldn't find a zener of the right voltage so I put 2 in series to get as close as possible. Worked fine.