Hello, I want is there anyone that has used a BJT instead of ultra low leakage diode(
- posted
14 years ago
Hello, I want is there anyone that has used a BJT instead of ultra low leakage diode(
Ebrahim wrote: Sorry I forgot to say that I mean Collector-Base Diode of BJT.
Regards
Do not think BJTs in general are that good; try an LED...
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
"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 !!!
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
What exactly are you trying to protect? IC, fet, ??
Hello, I'm Trying to protect input of Ultra low bias current FET OpAmps.
Regards, Ebrahim
In a way i have "measured" leakage current in LEDs; low microamps for remaining visibility which i think is astounding, and
Then a neon will not do as it takes around 60V to "break down" after ionizes; 90V beforehand.
Wow, uA and nA :-o ! then they can't be used as an ultra low leakage. Even humble 1N4148 has lower leakage ;) .
not cheap but
Nanoamps? Wow. Is that spec'd anywhere? If so then they'd be really useful as limiters.
-- Regards, Joerg http://www.analogconsultants.com/
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
*** 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 (
Cheers, 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
-- Dr Philip C D Hobbs Principal
"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 !!!
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
-- Dr Philip C D Hobbs Principal
*** 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
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