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I need a low current zener

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

Reply to
Klaus Kragelund
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On 2 Nov 2006 05:45:39 -0800, Klaus Kragelund wrote in Msg.

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

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robert

Reply to
Robert Latest

Robert Latest skrev:

Thanks - that answered my question :-)

Regards

Klaus

Reply to
Klaus Kragelund

Klaus Kragelund a écrit :

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.

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Thanks,
Fred.
Reply to
Fred Bartoli

LM4040/4041 series.

John

Reply to
John Larkin

Hello Klaus,

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.

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Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

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

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

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Bill Sloman, Nijmegen
Reply to
bill.sloman

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