BJTs as ultra low leakage protection diodes

Hello, I want is there anyone that has used a BJT instead of ultra low leakage diode(

Reply to
Ebrahim
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Ebrahim wrote: Sorry I forgot to say that I mean Collector-Base Diode of BJT.

Regards

Reply to
Ebrahim

Do not think BJTs in general are that good; try an LED...

Reply to
Robert Baer

Reply to
Phil Allison

Hello Robert :) Thanks for replying to my post. The main problem with LEDs is their low breakdown voltage. I have not measured leakage current of an LED but it makes sense because GaAs Reverse saturation current is about 10 times less than Si. Have you used LED as an ultra low leakage diode ? have you measured leakage currents of LEDs?

Regards, Ebrahim

Reply to
Ebrahim

"Ebrahim"

** You are a totally stupid pile of autistic shit, a waste of space a waster of good people's valuable time.

Fuck off and DROP DEAD !!!

Reply to
Phil Allison

Hello Robert :) Thanks for replying to my post. I have not measured leakage current of an LED but it makes sense because GaAs Reverse saturation current is about 10 times less than Si. Have you used LED as an ultra low leakage diode ? have you measured leakage currents of LEDs?

Regards, Ebrahim

Reply to
Ebrahim

What exactly are you trying to protect? IC, fet, ??

Reply to
miso

Hello, I'm Trying to protect input of Ultra low bias current FET OpAmps.

Regards, Ebrahim

Reply to
Ebrahim

In a way i have "measured" leakage current in LEDs; low microamps for remaining visibility which i think is astounding, and

Reply to
Robert Baer

Then a neon will not do as it takes around 60V to "break down" after ionizes; 90V beforehand.

Reply to
Robert Baer

Wow, uA and nA :-o ! then they can't be used as an ultra low leakage. Even humble 1N4148 has lower leakage ;) .

Reply to
Ebrahim

not cheap but

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Reply to
mook johnson

Nanoamps? Wow. Is that spec'd anywhere? If so then they'd be really useful as limiters.

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Regards, Joerg

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Reply to
Joerg

Then limit the current before you try to clamp it. You're not going to have a lot of luck finding a half-amp, 100V diode that leaks picoamps.

Why 100 volts? The opamp can't stand that.

Use a resistor or, if you can't stand the Johnson noise, a pair of depletion fets or some such. SSRs are interesting as low-resistance current limiters.

A high-value resistor bypassed with a small cap is interesting here too. If the fet has internal ESD diodes, that may be all you need.

John

Reply to
John Larkin

*** John: 100V is needed for another use(protecting a high voltage discrete amplifier), not protecting FET opamp. I was hoping that I could find one low leakage diode for both uses. though for the first application(HV Discrete amp) I can live with some leakage but for protecting the FET opamp I really need ultra low leakage and about 500mA load current.

*** The FET Opamp that I try to protect is opa627 (
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resistor is out of question because of Johnson noise as you mentioned(because voltage could rise up to 100V in some rare occasions and it needs a really big resistor) and for the same reason depletion FETs can't be used. SSR(Solid State Relays ?) How?
*** No, Ultra low bias current opamps usually do not have internal protection diodes.

Cheers, Ebrahim

Reply to
Ebrahim

It's far lower than that. I've measured ordinary red display LEDs whose leakage was below 100 fA from -5V to +0.5V bias.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

"Ebrahim"

"Ebrahim"

** You are a totally stupid pile of autistic shit, a waste of space a waster of good people's valuable time.

Fuck off and DROP DEAD !!!

Reply to
Phil Allison

What op amp have you ever seen that didn't, and how do you know? Such a device might be quite interesting in applications, but I don't know of one.

Even femtoamp leakage devices (e.g. the venerable LMC660) have protection diodes. You can use them for resetting integrators, by briefly inverting the power rails (with suitable current limits). Win Hill posted a circuit for that in this very group a few years back.

There are folks here who post stuff that's way beyond their competence...you've been here long enough to know who some of them are. Joining that group isn't necessarily the best way to achieve respect. Just saying.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs
Principal
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Reply to
Phil Hobbs

*** Hello Phil

Look at data sheet of OPA627, It has shown equivalent schematic. I do not see any protection diodes in inputs.

I really do not understand what you are talking about. I'm not here to join some internal groups, I'm not here to woo members. I'm not aware of factions of this newsgroup and honestly I do not care about them if they exist. I'm here to discuss technical issues. I never claim something that I'm not. I ask questions and if I know something about a topic I post my opinion. If someone provided documents and proved that I'm wrong about something, then I learn from him and thank him, provided that he present his reasons politely and respectfully. I do not remember I've claimed anything here. so your post really surprised me.

regards, Ebrahim

Reply to
Ebrahim

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