minimum zener current for break down.

dependent on voltage? For example, MMSZ5V1T1G (datasheet below) break down voltage Izt1 is given at test condition as 5ma.

sensing circuitry to less than 100uA. So after break down voltage of 5.6V, only few tens of uA will flow through the zener. Is this sufficient for the zener to break down and maintain the Vs - Vz for the voltage sensing circuitry?

--
No. 

Vz is specified with a certain current through the Zener. 

Take a look at quadrant 3 of the Cartesian plot on page 2 of the data 
sheet.

only dependent on voltage? For example, MMSZ5V1T1G (datasheet below) break down voltage Izt1 is given at test condition as 5ma.

tage sensing circuitry to less than 100uA. So after break down voltage of 5 .6V, only few tens of uA will flow through the zener. Is this sufficient fo r the zener to break down and maintain the Vs - Vz for the voltage sensing circuitry?

30K 5.6 volt regulator diodes do not have a sharp breakdown knee. They are Zener diodes. Higher voltage diodes are avalanche diodes and have a sharp knee. if you need a sharp knee, you may have to go to something like TL431.

Dan

it only dependent on voltage? For example, MMSZ5V1T1G (datasheet below) bre ak down voltage Izt1 is given at test condition as 5ma.

oltage sensing circuitry to less than 100uA. So after break down voltage of 5.6V, only few tens of uA will flow through the zener. Is this sufficient for the zener to break down and maintain the Vs - Vz for the voltage sensin g circuitry?

-->> Sensing Circuit

330K

May be important, zeners turn on SLOWLY!

To demonstrate, try to use two zeners in the feedback of an amplifier to make a 'square wave' generator. You'll see the zener's true characteristics.

only dependent on voltage? For example, MMSZ5V1T1G (datasheet below) break down voltage Izt1 is given at test condition as 5ma.

voltage sensing circuitry to less than 100uA. So after break down voltage of

5.6V, only few tens of uA will flow through the zener. Is this sufficient for the zener to break down and maintain the Vs - Vz for the voltage sensing circuitry?

They tend to have a lot of capacitance, and reverse recovery time. The zener mechanism itself is pretty fast.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators

t only dependent on voltage? For example, MMSZ5V1T1G (datasheet below) brea k down voltage Izt1 is given at test condition as 5ma.

ltage sensing circuitry to less than 100uA. So after break down voltage of

5.6V, only few tens of uA will flow through the zener. Is this sufficient f or the zener to break down and maintain the Vs - Vz for the voltage sensing circuitry?

Thanks. That graph doesn't have any values for zener break down current. Ho w do I find this from the datasheet?

Claimed to be sub-ns.

I'd always heard it was fast too, though I've never measured it.

Good point about how the reverse recovery messes that up if it's been forward biased. Pease's trick of putting the Zener inside a bridge rectifier sounds like pretty good medicine for that.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 USA 
+1 845 480 2058 

hobbs at electrooptical dot net 
http://electrooptical.net

dependent on voltage? For example, MMSZ5V1T1G (datasheet below) break down voltage Izt1 is given at test condition as 5ma.

sensing circuitry to less than 100uA. So after break down voltage of 5.6V, only few tens of uA will flow through the zener. Is this sufficient for the zener to break down and maintain the Vs - Vz for the voltage sensing circuitry?

Zeners "work" from zero to the max rated current (and above that, but do not do that). The problem is, that all voltages will have a noisy and negative resistance region. You better characterize the particular voltage and manufacturer that you think you want to use; you may find that there are NONE that do not have these undesirable characteristics in such low current regions. That is why the specs AVOID low currents and use "operating" or similar terms, and have NO I/V curves of value.

only dependent on voltage? For example, MMSZ5V1T1G (datasheet below) break down voltage Izt1 is given at test condition as 5ma.

sensing circuitry to less than 100uA. So after break down voltage of 5.6V, only few tens of uA will flow through the zener. Is this sufficient for the zener to break down and maintain the Vs - Vz for the voltage sensing circuitry?

Most of the Japanese parts are well specified, and the Iz currents are reasonable (like 0.5mA and not 20mA or whatever).

Eg.

5.6V nominal at 5mA, 'typical' curve down to 1uA, up to 100mA

5.6V nominal at 500uA, 'typical' curve down to 1uA, up to 10mA

Seems many designers these days would rather use a $3 chip than a $0.03 zener.

Just guessing about what you are actually trying to do, but the Rohm part looks like it might 'typically' be suitable. Maybe you could use a higher voltage zener if your input switches between 5V and 30V- the

5.6V unit is guaranteed to have < 0.5uA at 2.5V. A 9.1V zener from that series is guaranteed to have a reverse current of < 0.5uA at 6V and will drop no more than 9.2V at 5mA, so at 5V in you'd have less than 24mV to your sensing circuit, and at 30V you'd have more than about 21V.

No one can tell anything from your question, you don't even specify what im pedance or voltage is at the sensing circuit, you don't mention how much lo ading the 5-30V source can handle, you don't tell anything about whether yo u're trying to detect just the presence of input in 5-30V range or actually measure its value or how the sensor determines it. The circuit you have dr awn is HIGHLY unusual for a voltage clamp with the 47K to GND.

only dependent on voltage? For example, MMSZ5V1T1G (datasheet below) break down voltage Izt1 is given at test condition as 5ma.

voltage sensing circuitry to less than 100uA. So after break down voltage of

5.6V, only few tens of uA will flow through the zener. Is this sufficient for the zener to break down and maintain the Vs - Vz for the voltage sensing circuitry?

--
Yes, it does.

dependent on voltage? For example, MMSZ5V1T1G (datasheet below) break down voltage Izt1 is given at test condition as 5ma.

sensing circuitry to less than 100uA. So after break down voltage of 5.6V, only few tens of uA will flow through the zener. Is this sufficient for the zener to break down and maintain the Vs - Vz for the voltage sensing circuitry?

That's a rather strange way to detect anything over 5 volts? I mean, that is what it looks like you're doing?

If that is your aim, I would use an NPN transistor with an emitter bias of 4.5 volts for example and have the collector bias the next stage. THe base input would be the input from the 5-30 volts via a R ofcourse.. Put a 35 volt TVS diode on the front end for protection..

--
  Jamie

Characterizing components is always a good thing. Depending on the numbers is another story. If it is not in the datasheet, the number can always change. So you play the "what if" game. What if XXX doubled? What if XXX were cut in half? That is, you determine the sensitivity of your design to this undocumented parameter.

This presumes some product you will be selling in the hundreds of thousands to millions per year over the next decade. If you just need a few units, then characterization data should be fine.

impedance or voltage is at the sensing circuit, you don't mention how much loading the 5-30V source can handle, you don't tell anything about whether you're trying to detect just the presence of input in 5-30V range or actual ly measure its value or how the sensor determines it. The circuit you have drawn is HIGHLY unusual for a voltage clamp with the 47K to GND.

All I am trying to do is to find the voltage is above 6V approx or not by s ensing the remaining voltage after the zener drop.

only dependent on voltage? For example, MMSZ5V1T1G (datasheet below) break down voltage Izt1 is given at test condition as 5ma.

voltage sensing circuitry to less than 100uA. So after break down voltage of

5.6V, only few tens of uA will flow through the zener. Is this sufficient for the zener to break down and maintain the Vs - Vz for the voltage sensing circuitry?

A 5.6V zener essentially does not count WRT to negative resistance and noise at low currents; I should have been more eXplicit - should have said "avalanche". Note that 9V zener does "count"; runs in avalanche mode and current spec is much higher than what the OP mentioned.

From the table below the graph:

Vz1@IZt1, Vz2@IZt2.

--
"For a successful technology, reality must take precedence  
over public relations, for nature cannot be fooled." 
                                       (Richard Feynman)

It's Google, expect the unexpected.

--
"For a successful technology, reality must take precedence  
over public relations, for nature cannot be fooled." 
                                       (Richard Feynman)

what impedance or voltage is at the sensing circuit, you don't mention how much loading the 5-30V source can handle, you don't tell anything about whether you're trying to detect just the presence of input in 5-30V range or actually measure its value or how the sensor determines it. The circuit you have drawn is HIGHLY unusual for a voltage clamp with the

47K to GND.

by sensing the remaining voltage after the zener drop.

In that case a micropower variant of a TLV431, a few resistors and a mocropower comparator would be a far better choice. You should be able to get your power under 10 uA easy, and near or even less that 1 uA if you try hard.

?-)