Minimum current for zener diodes

most zeners need more than 50nA. 1 uA is plenty

It's in the datasheet, did you miss it?

Bad zener? "not seem good" in what way? 500uA is enough, C5V6 should get between 5.2 to 6V according to one datasheet I looked at.

It's an interesting question, and the answer is complicated and varies with the breakdown voltage.

Low voltage "zener" diodes break down by the Zener mechanism, while at higher voltages, avalanche breakdown takes over

eakdown.html

Your 5.6V diodes sit right on the border between the two mechanisms and both are likely to be active.

Avalanche breakdown tends to be noisy at low currents - the actual areas in which the avalanches occurs tends to be tiny, so at "low" currents (less than a milliamp) there may be only one electron in transit at any one moment. The process by which this electron creates new charge carriers is statistical, and if that one electron doesn't succeed in generating at least one new charge carrier as as it makes its way across the junction, the current stops for a bit until thermal noise eventually promotes another charge carrier into the conduction band, giving you are rather jagged voltage-versus time curve.

Search on "micro-plasmas" and note that glass-packaged zener diodes tend to behave different when exposed to light (and have been known to emit light when carrying current).

The Zener mechanism seems to be quieter.

There was a nice - tolerably long - thread on the subject - "Zener Diode Oscillation" - here back in 1997. Winfield Hill and the late Tony Williams posted a lot of interesting measurements and some interesting references from the semiconductor physics literature.

-- Bill Sloman, Nijmegen

--
For a Zener to "work properly" the current through it should be as
specified on the data sheet:

http://www.rectron.com/data_sheets/bzx55c-bs.pdf

There's some nice graphs in the General Semi data sheet here.

The low voltage zeners have really mushy corner's, the dynamic impedance is pretty poor if you just barely turn them 'on'.

At 2mA it looks like the C5V6 is still in the corner of the I-V. You can run the higher voltage zeners at lower current... 'course as Bill point out they are noiser. Why do you want to run at the minimum current?

George H.

5 milliamps is on the spec sheet

The TempCo of Zeners depends on the current, too. No wonders, TempCo is minimal at the recommended current. TempCo is typically positive for lower currents and negative for higher currents.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

In my experience you'll need at least several mA (say about 4mA) through a zener to get it operating at its specified voltage.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
--------------------------------------------------------------

We seem to have a "random rattling" issue here.

Did _anyone_ pay attention to Field's post showing that the I VALUE is specified on the data sheet?

And ALL "zener's" have an Ohmic term. To get really steep slope you need to use an active device, such as a TL431. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
         Obama is not the solution, Obama is the problem!

--
Zener current only affects the _slope_ of the tempco in a minor way,
while Zener voltage affects both the sign _and_ the slope in a major
way. 

Below about 5 volts the diode is in "Zener" mode and exhibits a
negative tempco, while above about 5 volts it's operating in
"avalanche" mode and exhibits a positive tempco.

Here are some excerpts from the 1980 Motorola Zener Diode Manual for
your perusal:

news:ck6os61esk28lnkh18e7fra8ro810ekgtj@4ax.com

Hello Sonnich,

The minimum current depends on what is acceptable for you (so for you this answer isn't useful).

If you want to go a step further below mA range, you may try a low voltage avalanche diode like PLVA2600A. This series is specified at current well below 1 mA.

Kind regards,

Wim PA3DJS

Yes, you are right.

LOL, I had a board today where a 220K res had been fitted instead of 220R. Instead of +15V, I got -1.5V.( +/- 18V5 to +/- 15V via zeners)

here.http://www.datasheetcatalog.com/datasheets_pdf/B/Z/X/5/BZX55-C5V6.shtml

You stated "most zeners need more than 50nA. 1 uA is plenty" in a previous message.

--
You can't fix stupid. You can't even put a Band-Aid? on it, because it's
Teflon coated.

I run on battery power, and need to limit my current. I read below, that TL431 is another option - I will give that some toughts, as that might be the solution, more exact and only slightly more expensive.

If it takes 5mA, then the question is - is a 78L05 or LM317LZ better? I need the 5V for powering a panelmeter from a 12V battery. It takes

1mA. The LM317LZ has a minimum load of 3-5mA, which will force me to fry it off. The loss will be the same, but I will get a more stable power.

Sonnich

I run on battery power, and need to limit my current. I read below, that TL431 is another option - I will give that some toughts, as that might be the solution, more exact and only slightly more expensive.

If it takes 5mA, then the question is - is a 78L05 or LM317LZ better? I need the 5V for powering a panelmeter from a 12V battery. It takes

1mA. The LM317LZ has a minimum load of 3-5mA, which will force me to fry it off. The loss will be the same, but I will get a more stable power.

Sonnich

Plenty of 5V LDO regulators that only take 2-3 microamps.... take a look at Microchip.com

n

Checked it out. Seems like the 79L05 (for my need) will work with a load of 1mA, fine for me, and I-bias @ max 6mA. I will check hot much is it really it tomorrow. Otherwise LM317/337 will work with a minimum load of ~2mA, app the same. Considering the resistors needed, it will work as well.

Which brings me to protection - overvoltage protection (the charger has fried 3 ICs as of now)(even that it can be fixed, protection is always a good thing). I was thinking of doing this by a transistor, zener and resistor, which would work. But an 78L12 or 15 can do the same, and it should let the voltage through and still work.

Using a 78L15 and 79L05 would do it, it is cheap, and require fewer components, and the power used is the same (or less)

How much is there to discuss?

Sonnich

I run on battery power, and need to limit my current. I read below, that TL431 is another option - I will give that some toughts, as that might be the solution, more exact and only slightly more expensive.

If it takes 5mA, then the question is - is a 78L05 or LM317LZ better? I need the 5V for powering a panelmeter from a 12V battery. It takes

1mA. The LM317LZ has a minimum load of 3-5mA, which will force me to fry it off. The loss will be the same, but I will get a more stable power.

Sonnich

n

If you want a low current voltage reference, don't use a zener diode.

Miinimal goggling gave me this

and Analog Devices have got parts with supply currents down to 12uA

The ADR293 offers 5V at 15uA

I've not used any of these parts, so I don't know what the downsides are. but there does seem to be a lot of stuff available that would do your job better than a zener diode.

-- Bill Sloman, Nijmegen