I need a low current zener

[Klaus Kragelund]

Hi

In a low current power supply I need a zener that in the combination
with a pull-up resistor provides a reference voltage. But, I cannot
drive large currents (more than 100uA) through a standard zener
(BZX84C5V6) to get a stable zener voltage

So I looked at the BZX99 from philips which looked good at a first
glance. But the differential resistance is about 1000ohms at low
currents (100uA), so this won't work since the bias current for the
zener can range from 100uA to 1mA

Has anyone come accross a better zener?

Thanks

Klaus

 

[Robert Latest]

On 2 Nov 2006 05:45:39 -0800,

Has anyone come accross a better zener?

A few weeks ago there was a long and detailed thread about this
topic:

http://groups.google.com/group/sci.electronics.design/browse_frm/
thread/a6e3feb619b54131/1950d900e6c65dc4?tvc=1&q=group%3A
sci.electronics.design+insubject%3Azener&hl=en#1950d900e6c65dc4

robert

 

[Klaus Kragelund]

Robert Latest skrev:

On 2 Nov 2006 05:45:39 -0800,


A few weeks ago there was a long and detailed thread about this
topic:

http://groups.google.com/group/sci.electronics.design/browse_frm/
thread/a6e3feb619b54131/1950d900e6c65dc4?tvc=1&q=group%3A
sci.electronics.design+insubject%3Azener&hl=en#1950d900e6c65dc4

robert

Thanks - that answered my question

Regards

Klaus

 

[Fred Bartoli]

Klaus Kragelund a écrit :

Hi

In a low current power supply I need a zener that in the combination
with a pull-up resistor provides a reference voltage. But, I cannot
drive large currents (more than 100uA) through a standard zener
(BZX84C5V6) to get a stable zener voltage

So I looked at the BZX99 from philips which looked good at a first
glance. But the differential resistance is about 1000ohms at low
currents (100uA), so this won't work since the bias current for the
zener can range from 100uA to 1mA

Has anyone come accross a better zener?

Does your shunt ref has to supply varying current or not?
Or do you mean that the supply you ref is derived from changes a lot?

Is you're drawing zero or constant current from your ref, then a single
BJT and resistor will do the trick:


VCC
+
|
.-.
| |
| |
'-'
|
+------.
| |
| .-.
| | |
| | | 6K8
| '-'

| |

|----+-------> ref
/| |
| |
| z
=== A 5V6
GND |
|
===
GND


You can also use some bandgap ref. which will bring you more accuracy.
TLV431 start at 80uA and LM385 adj start at 10uA.

 

[John Larkin]

Hi

In a low current power supply I need a zener that in the combination
with a pull-up resistor provides a reference voltage. But, I cannot
drive large currents (more than 100uA) through a standard zener
(BZX84C5V6) to get a stable zener voltage

So I looked at the BZX99 from philips which looked good at a first
glance. But the differential resistance is about 1000ohms at low
currents (100uA), so this won't work since the bias current for the
zener can range from 100uA to 1mA

Has anyone come accross a better zener?

Thanks

Klaus

LM4040/4041 series.

John

 

[Joerg]

Hello Klaus,

In a low current power supply I need a zener that in the combination
with a pull-up resistor provides a reference voltage. But, I cannot
drive large currents (more than 100uA) through a standard zener
(BZX84C5V6) to get a stable zener voltage

So I looked at the BZX99 from philips which looked good at a first
glance. But the differential resistance is about 1000ohms at low
currents (100uA), so this won't work since the bias current for the
zener can range from 100uA to 1mA

Has anyone come accross a better zener?

Short answer: No. I have tried quite hard a while ago and it turns out
that the typical "low current zener" is really a normal zener with a
gussied up data sheet. As you have already seen that means they are
operated in their knee and are thus mushy. Plus sooner or later you'll
find yourself in a line-stop situation because a batch ran out of
tolerance. One of my clients did :-(

If you can stomach a few cents more per unit consider what Fred had
suggested: The TLV431 which is also multi-sourced. I have redesigned
several products from zener to TLV and there was never again a problem
with those.

 

[[email protected]]

Hi

In a low current power supply I need a zener that in the combination
with a pull-up resistor provides a reference voltage. But, I cannot
drive large currents (more than 100uA) through a standard zener
(BZX84C5V6) to get a stable zener voltage

So I looked at the BZX99 from philips which looked good at a first
glance. But the differential resistance is about 1000ohms at low
currents (100uA), so this won't work since the bias current for the
zener can range from 100uA to 1mA

Has anyone come accross a better zener?

Analog Devices came up with some low-current FET based references a few
years ago

http://www.analog.com/UploadedFiles/Data_Sheets/ADR291_292.pdf

They seems to have stocks of the ADR291GRZ at a couple of bucks each.