Not OT: BC850 as a diode clamp?

It might just be that Vbe is more tightly specified than forward voltage of a regular diode.

https://assets.nexperia.com/documents/data-sheet/BC849_BC850.pdf

It is shown as min 580mV, typ 660mV and max 700mV at 2mA and 25C, which is pretty tight, and unusually detailed. there's no minimum voltage at 10mA.

--
Bill Sloman, Sydney

Fred Bloggs

2023-01-29 17:41:41 UTC

It might just be that Vbe is more tightly specified than forward voltage of a regular diode.
https://assets.nexperia.com/documents/data-sheet/BC849_BC850.pdf
It is shown as min 580mV, typ 660mV and max 700mV at 2mA and 25C, which is pretty tight, and unusually detailed. there's no minimum voltage at 10mA.

https://www.researchgate.net/figure/Practical-ECG-amplifier-circuit_fig2_258847810

https://pubmed.ncbi.nlm.nih.gov/16594298/

The details are behind registration walls- so I'm not going to bother going any further- it's a "pest" post.

It's a high impedance difference input amp running off 1.8V, probably floating, so they're really concerned about rejecting pickup on the electrode leads, in addition to the precision. I notice TI calls out the OPA333 for it's extraordinary CMRR out to 250MHz, so there's a concern regarding RF reception as well. Looks like it's a self-correcting offset RRIO amplifier.

As for the exact choice of BC850, you tell us.

Post by Anthony William Sloman
--
Bill Sloman, Sydney

John Larkin

2023-01-29 18:24:26 UTC

On Sun, 29 Jan 2023 09:41:41 -0800 (PST), Fred Bloggs

It might just be that Vbe is more tightly specified than forward voltage of a regular diode.
https://assets.nexperia.com/documents/data-sheet/BC849_BC850.pdf
It is shown as min 580mV, typ 660mV and max 700mV at 2mA and 25C, which is pretty tight, and unusually detailed. there's no minimum voltage at 10mA.

https://www.researchgate.net/figure/Practical-ECG-amplifier-circuit_fig2_258847810
https://pubmed.ncbi.nlm.nih.gov/16594298/
The details are behind registration walls- so I'm not going to bother going any further- it's a "pest" post.
It's a high impedance difference input amp running off 1.8V, probably floating, so they're really concerned about rejecting pickup on the electrode leads, in addition to the precision. I notice TI calls out the OPA333 for it's extraordinary CMRR out to 250MHz, so there's a concern regarding RF reception as well. Looks like it's a self-correcting offset RRIO amplifier.
As for the exact choice of BC850, you tell us.

The opamps run single-ended so don't need much cmrr. CM will be
dominated by resistor and capacitor tolerances.

Horrible mess. Why not buy one good diffamp?

Ricky

2023-01-29 18:27:38 UTC

Post by John Larkin
On Sun, 29 Jan 2023 09:41:41 -0800 (PST), Fred Bloggs

It might just be that Vbe is more tightly specified than forward voltage of a regular diode.
https://assets.nexperia.com/documents/data-sheet/BC849_BC850.pdf
It is shown as min 580mV, typ 660mV and max 700mV at 2mA and 25C, which is pretty tight, and unusually detailed. there's no minimum voltage at 10mA.

https://www.researchgate.net/figure/Practical-ECG-amplifier-circuit_fig2_258847810
https://pubmed.ncbi.nlm.nih.gov/16594298/
The details are behind registration walls- so I'm not going to bother going any further- it's a "pest" post.
It's a high impedance difference input amp running off 1.8V, probably floating, so they're really concerned about rejecting pickup on the electrode leads, in addition to the precision. I notice TI calls out the OPA333 for it's extraordinary CMRR out to 250MHz, so there's a concern regarding RF reception as well. Looks like it's a self-correcting offset RRIO amplifier.
As for the exact choice of BC850, you tell us.

The opamps run single-ended so don't need much cmrr. CM will be
dominated by resistor and capacitor tolerances.
Horrible mess. Why not buy one good diffamp?

If you read a few of his articles, you might learn something. The guy is not just another pretty face.

--
Rick C.

--+ Get 1,000 miles of free Supercharging
--+ Tesla referral code - https://ts.la/richard11209

Fred Bloggs

2023-01-29 18:31:07 UTC

Post by John Larkin
On Sun, 29 Jan 2023 09:41:41 -0800 (PST), Fred Bloggs

It might just be that Vbe is more tightly specified than forward voltage of a regular diode.
https://assets.nexperia.com/documents/data-sheet/BC849_BC850.pdf
It is shown as min 580mV, typ 660mV and max 700mV at 2mA and 25C, which is pretty tight, and unusually detailed. there's no minimum voltage at 10mA.

https://www.researchgate.net/figure/Practical-ECG-amplifier-circuit_fig2_258847810
https://pubmed.ncbi.nlm.nih.gov/16594298/
The details are behind registration walls- so I'm not going to bother going any further- it's a "pest" post.
It's a high impedance difference input amp running off 1.8V, probably floating, so they're really concerned about rejecting pickup on the electrode leads, in addition to the precision. I notice TI calls out the OPA333 for it's extraordinary CMRR out to 250MHz, so there's a concern regarding RF reception as well. Looks like it's a self-correcting offset RRIO amplifier.
As for the exact choice of BC850, you tell us.

The opamps run single-ended so don't need much cmrr. CM will be
dominated by resistor and capacitor tolerances.
Horrible mess. Why not buy one good diffamp?

They're talking about uV level stuff appearing right up on the OA inputs. If you're dealing with mV signal levels, uV is only 60dB down.

Fred Bloggs

2023-01-29 18:33:12 UTC

Post by John Larkin
On Sun, 29 Jan 2023 09:41:41 -0800 (PST), Fred Bloggs

It might just be that Vbe is more tightly specified than forward voltage of a regular diode.
https://assets.nexperia.com/documents/data-sheet/BC849_BC850.pdf
It is shown as min 580mV, typ 660mV and max 700mV at 2mA and 25C, which is pretty tight, and unusually detailed. there's no minimum voltage at 10mA.

https://www.researchgate.net/figure/Practical-ECG-amplifier-circuit_fig2_258847810
https://pubmed.ncbi.nlm.nih.gov/16594298/
The details are behind registration walls- so I'm not going to bother going any further- it's a "pest" post.
It's a high impedance difference input amp running off 1.8V, probably floating, so they're really concerned about rejecting pickup on the electrode leads, in addition to the precision. I notice TI calls out the OPA333 for it's extraordinary CMRR out to 250MHz, so there's a concern regarding RF reception as well. Looks like it's a self-correcting offset RRIO amplifier.
As for the exact choice of BC850, you tell us.

The opamps run single-ended so don't need much cmrr. CM will be
dominated by resistor and capacitor tolerances.

The non-inverting configuration is self-corrupting with CMRR.

Post by John Larkin
Horrible mess. Why not buy one good diffamp?

piglet

2023-01-29 10:34:43 UTC

Post by Ricky
A differential input amp is using BC850 transistors with the base tied to the collector as a clamp to ground. What is better about this than a diode? I guess it can handle a lot more current before the voltage starts to rise?
https://html.scribdassets.com/9r5y0a5pxc35p3zy/images/4-1adb6b3466.jpg

Low leakage and lower dynamic resistance due to transistor action.

piglet

Gerhard Hoffmann

2023-01-29 11:56:13 UTC

Post by Ricky
A differential input amp is using BC850 transistors with the base tied
to the collector as a clamp to ground. What is better about this than
a diode? I guess it can handle a lot more current before the voltage
starts to rise?
https://html.scribdassets.com/9r5y0a5pxc35p3zy/images/4-1adb6b3466.jpg

Low leakage and lower dynamic resistance due to transistor action.
piglet

Someone at NIST built a complete ring mixer around that structure.

< https://tf.nist.gov/general/pdf/2556.pdf >

Gerhard

Mike Monett VE3BTI

2023-01-29 12:34:55 UTC

Post by Gerhard Hoffmann
Someone at NIST built a complete ring mixer around that structure.
< https://tf.nist.gov/general/pdf/2556.pdf >
Gerhard

+1. Thanks

--
MRM

John Larkin

2023-01-29 15:31:01 UTC

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.

That's a really weird circuit.

Lasse Langwadt Christensen

2023-01-29 15:41:19 UTC

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

it sorta works like a zener diode

Ricky

2023-01-29 18:03:30 UTC

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

it sorta works like a zener diode
http://youtu.be/BGcKjy_UNQ4

Not exactly the same circuit. The schematic in question grounds the collector/base connection, so the two transistors work independently. I suppose it does however, give you the same effect, by clamping like a diode at 0.6V below ground, and some zener-like effect above ground. I didn't think of that, but it suits the circuits this guy designs I suppose. I need to remember this one. I don't think I can use it in my current design though. That is clamped to the power rails on the analog inputs, ±12V. I may need to rethink that circuit for other reasons though. The input switches are hard to find.

--
Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

John Larkin

2023-01-29 18:15:08 UTC

On Sun, 29 Jan 2023 07:41:19 -0800 (PST), Lasse Langwadt Christensen

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

it sorta works like a zener diode
http://youtu.be/BGcKjy_UNQ4

But why? The BAV99 already clamps up and down. I assume the supply is
5 volts, split-rail at 2.5, so the BAV clamps at +-3 roughly.

Of course the split supply is soft.

Very weird circuit.

Ricky

2023-01-29 18:25:51 UTC

Post by John Larkin
On Sun, 29 Jan 2023 07:41:19 -0800 (PST), Lasse Langwadt Christensen

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

it sorta works like a zener diode
http://youtu.be/BGcKjy_UNQ4

But why? The BAV99 already clamps up and down. I assume the supply is
5 volts, split-rail at 2.5, so the BAV clamps at +-3 roughly.
Of course the split supply is soft.
Very weird circuit.

Only to someone who doesn't understand it. The BAV diodes clamp to the power rails, which means a heavy surge can overload every part on the board. In this design the BC850 acts as a higher current path to ground for the bulk of the overvoltage. Grounds can typically handle that sort of thing better than power rails.

--
Rick C.

++ Get 1,000 miles of free Supercharging
++ Tesla referral code - https://ts.la/richard11209

Lasse Langwadt Christensen

2023-01-29 18:56:11 UTC

Post by John Larkin
On Sun, 29 Jan 2023 07:41:19 -0800 (PST), Lasse Langwadt Christensen

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

it sorta works like a zener diode
http://youtu.be/BGcKjy_UNQ4

But why? The BAV99 already clamps up and down. I assume the supply is
5 volts, split-rail at 2.5, so the BAV clamps at +-3 roughly.

until you push too much current in to the supply

the BAV99s are not really needed the opamp is rated for +/-10mA into the input

Ricky

2023-01-29 19:04:26 UTC

Post by John Larkin
On Sun, 29 Jan 2023 07:41:19 -0800 (PST), Lasse Langwadt Christensen

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

it sorta works like a zener diode
http://youtu.be/BGcKjy_UNQ4

But why? The BAV99 already clamps up and down. I assume the supply is
5 volts, split-rail at 2.5, so the BAV clamps at +-3 roughly.

until you push too much current in to the supply
the BAV99s are not really needed the opamp is rated for +/-10mA into the input

I typically use Schottky diodes for this, to get the lower Vf.

--
Rick C.

-+- Get 1,000 miles of free Supercharging
-+- Tesla referral code - https://ts.la/richard11209

Lasse Langwadt Christensen

2023-01-29 20:06:32 UTC

Post by Ricky

Post by John Larkin
On Sun, 29 Jan 2023 07:41:19 -0800 (PST), Lasse Langwadt Christensen

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

it sorta works like a zener diode
http://youtu.be/BGcKjy_UNQ4

But why? The BAV99 already clamps up and down. I assume the supply is
5 volts, split-rail at 2.5, so the BAV clamps at +-3 roughly.

until you push too much current in to the supply
the BAV99s are not really needed the opamp is rated for +/-10mA into the input

I typically use Schottky diodes for this, to get the lower Vf.

sure, but they also have higher leakage current

the point was that according to the datasheet as long as the current is limited to +/-10mA
it is ok to use the ESD diodes

Phil Hobbs

2023-01-29 20:27:32 UTC

Post by Ricky

Post by John Larkin
On Sun, 29 Jan 2023 07:41:19 -0800 (PST), Lasse Langwadt Christensen

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

it sorta works like a zener diode
http://youtu.be/BGcKjy_UNQ4

But why? The BAV99 already clamps up and down. I assume the supply is
5 volts, split-rail at 2.5, so the BAV clamps at +-3 roughly.

until you push too much current in to the supply
the BAV99s are not really needed the opamp is rated for +/-10mA into the input

I typically use Schottky diodes for this, to get the lower Vf.

sure, but they also have higher leakage current

And much lower shunt resistance.

Post by Lasse Langwadt Christensen
the point was that according to the datasheet as long as the current is limited to +/-10mA
it is ok to use the ESD diodes

(Responding in a new thread)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

Ricky

2023-01-29 21:03:25 UTC

Post by Ricky

Post by John Larkin
On Sun, 29 Jan 2023 07:41:19 -0800 (PST), Lasse Langwadt Christensen

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

it sorta works like a zener diode
http://youtu.be/BGcKjy_UNQ4

But why? The BAV99 already clamps up and down. I assume the supply is
5 volts, split-rail at 2.5, so the BAV clamps at +-3 roughly.

until you push too much current in to the supply
the BAV99s are not really needed the opamp is rated for +/-10mA into the input

I typically use Schottky diodes for this, to get the lower Vf.

sure, but they also have higher leakage current
the point was that according to the datasheet as long as the current is limited to +/-10mA
it is ok to use the ESD diodes

Why would anyone care about the leakage current? This design is AC coupled. DC is not being measured. Let 'er leak!

--
Rick C.

-++ Get 1,000 miles of free Supercharging
-++ Tesla referral code - https://ts.la/richard11209

Phil Hobbs

2023-01-29 21:34:36 UTC

In one hand-wired proto recently,(*) I was using an LM319N
open-collector dual comparator to drive the !set and !clear inputs of
one section of a 74VHC74A dflop.

The 319 was running off +-15V. By mistake, I wired the pull-up resistor
on one section to +15 rather than +5. The circuit worked perfectly--I
only noticed the blunder when I went to make a slight change to the ramp
current source.

Abs max on both VDD and any input is +7V, which appears to be a fairly
absurd underestimate of what the !clear input can comfortably manage, at
least for a day or two. It didn't seem to be drawing any input current,
either--at most a few dozen microamps.

Cheers

Phil Hobbs

(*) It was that highly linear ramp generator I was talking about in
another thread. Swapping out the mylar cap for a polypropylene reduced
the soakage tail on the ramp, but didn't eliminate it.

bitrex

2023-01-29 22:32:32 UTC

In one hand-wired proto recently,(*) I was using an LM319N
open-collector dual comparator to drive the !set and !clear inputs of
one section of a 74VHC74A dflop.
The 319 was running off +-15V. By mistake, I wired the pull-up resistor
on one section to +15 rather than +5. The circuit worked perfectly--I
only noticed the blunder when I went to make a slight change to the ramp
current source.
Abs max on both VDD and any input is +7V, which appears to be a fairly
absurd underestimate of what the !clear input can comfortably manage, at
least for a day or two. It didn't seem to be drawing any input current,
either--at most a few dozen microamps.
Cheers
Phil Hobbs
(*) It was that highly linear ramp generator I was talking about in
another thread. Swapping out the mylar cap for a polypropylene reduced
the soakage tail on the ramp, but didn't eliminate it.

you ever try them xicon polystyrenes:

<https://www.mouser.com/c/passive-components/capacitors/film-capacitors/?q=xicon%20polystyrene&voltage%20rating%20dc=50%20VDC&sort=pricing%7C1>

They're real nice, glad they haven't <knock on wood> discontinued 'em yet

Clifford Heath

2023-01-29 23:34:52 UTC

In one hand-wired proto recently,(*) I was using an LM319N
open-collector dual comparator to drive the !set and !clear inputs of
one section of a 74VHC74A dflop.
The 319 was running off +-15V. By mistake, I wired the pull-up resistor
on one section to +15 rather than +5. The circuit worked perfectly--I
only noticed the blunder when I went to make a slight change to the ramp
current source.
Abs max on both VDD and any input is +7V, which appears to be a fairly
absurd underestimate of what the !clear input can comfortably manage, at
least for a day or two. It didn't seem to be drawing any input current,
either--at most a few dozen microamps.

Possibly such high-speed parts dispense with ESD diodes to reduce input
capacitance?

Clifford Heath

Lasse Langwadt Christensen

2023-01-29 23:56:36 UTC

Post by Clifford Heath

Post by Phil Hobbs
In one hand-wired proto recently,(*) I was using an LM319N
open-collector dual comparator to drive the !set and !clear inputs of
one section of a 74VHC74A dflop.
The 319 was running off +-15V. By mistake, I wired the pull-up resistor
on one section to +15 rather than +5. The circuit worked perfectly--I
only noticed the blunder when I went to make a slight change to the ramp
current source.
Abs max on both VDD and any input is +7V, which appears to be a fairly
absurd underestimate of what the !clear input can comfortably manage, at
least for a day or two. It didn't seem to be drawing any input current,
either--at most a few dozen microamps.

Possibly such high-speed parts dispense with ESD diodes to reduce input
capacitance?

usually so they can be 5V tolerant and/or handle input while not powered

Clifford Heath

2023-01-30 01:50:25 UTC

Post by Clifford Heath

Possibly such high-speed parts dispense with ESD diodes to reduce input
capacitance?

usually so they can be 5V tolerant and/or handle input while not powered

Right, but it probably helps reduce C too.

Did this response come up in the wrong thread for everyone else too?

Lasse, your news client is weird.

CH.

Mike Monett VE3BTI

2023-01-29 22:10:58 UTC

Post by John Larkin
That's a really weird circuit.

it sorta works like a zener diode
http://youtu.be/BGcKjy_UNQ4

That circuit has a big advantage. The capacitance of a reverse-biased BE
junction is very low, so it should be much faster than a Zener.

However, the power capability is extremely low since the junction area is
so small.

The circuit may be useful for transient events, but a sustained overload
may short the BE junction, rendering the circuit useless.

The operating voltage is limited to around 6 volts, which is the breakdown
voltage of most common NPN transistors. There is no information on the
temperature coefficient of the reverse-biased BE junction, so the circuit
has limited application in precision regulators.

In addition, breaking down the BE junction will probable damage the
junction and degrade the noise figure of the transistor, rendering it
useless for low level amplification.

--
MRM

Phil Hobbs

2023-01-30 00:43:55 UTC

Post by John Larkin
That's a really weird circuit.

it sorta works like a zener diode
http://youtu.be/BGcKjy_UNQ4

That circuit has a big advantage. The capacitance of a reverse-biased BE
junction is very low, so it should be much faster than a Zener.

There are USB ESD protectors that are much, much better.

Cheers

Phil Hobbs

Mike Monett VE3BTI

2023-01-30 00:52:00 UTC

Post by Lasse Langwadt Christensen
it sorta works like a zener diode
http://youtu.be/BGcKjy_UNQ4

That circuit has a big advantage. The capacitance of a reverse-biased BE
junction is very low, so it should be much faster than a Zener.

There are USB ESD protectors that are much, much better.
Cheers
Phil Hobbs

Any links?

--
MRM

Phil Hobbs

2023-01-30 01:08:49 UTC

Post by Lasse Langwadt Christensen
it sorta works like a zener diode
http://youtu.be/BGcKjy_UNQ4

That circuit has a big advantage. The capacitance of a reverse-biased BE
junction is very low, so it should be much faster than a Zener.

There are USB ESD protectors that are much, much better.
Cheers
Phil Hobbs

Any links?

The ones we've used are

IC TVS 4X USB ZENER ESD BEEFY TSSOP8 SN75240PWR TI
$0.57815 @ qty 1000

IC TVS 2X USB ESD DIODES+ZENER 5.5V XSON-6 PRTR5V0U2F,115
Nexperia $0.16539 @ qty 1000

Cheers

Phil Hobbs

Mike Monett VE3BTI

2023-01-30 03:54:34 UTC

Post by Mike Monett VE3BTI
Any links?
The ones we've used are
IC TVS 4X USB ZENER ESD BEEFY TSSOP8 SN75240PWR TI
IC TVS 2X USB ESD DIODES+ZENER 5.5V XSON-6 PRTR5V0U2F,115
Cheers
Phil Hobbs

Thanks. The datasheet is at

https://www.ti.com/lit/ds/symlink/sn75240.pdf

The circuit is on Page 6, Figure 9-1. TVS Structure and Current Voltage
Characteristic

Page 1 states:

"The input capacitance of 35 pF makes it unsuitable for high-speed USB 2.0
applications."

This means they they are only suitable for USB version 1.1 at 12 Mbps, but
not many people are using this anymore.

So what do IC's use for ESD protection? I don't know, but I suspect it is
reverse-biased diodes to VCC and GND, similar to the PRTR5V0U2F, at

https://assets.nexperia.com/documents/data-sheet/PRTR5V0U2F_PRTR5V0U2K.pdf

The waveforms on Page 6, Fig 4. ESD clamping test setup and waveforms, show
very significant reduction in ESD amplitudes, from 800V peak to 20V peak.

In addition, the low capacitance of 1 pF enables their use in higher speed
USB applications. Cheaper and much better performance than the 75240.

However, I wonder if it is really needed, since many ICs are already rated
for ESD protection up to 8 kV.

--
MRM

Phil Hobbs

2023-01-30 09:08:02 UTC

Post by Mike Monett VE3BTI
Any links?
The ones we've used are
IC TVS 4X USB ZENER ESD BEEFY TSSOP8 SN75240PWR TI
IC TVS 2X USB ESD DIODES+ZENER 5.5V XSON-6 PRTR5V0U2F,115
Cheers
Phil Hobbs

Thanks. The datasheet is at
https://www.ti.com/lit/ds/symlink/sn75240.pdf
The circuit is on Page 6, Figure 9-1. TVS Structure and Current — Voltage
Characteristic
"The input capacitance of 35 pF makes it unsuitable for high-speed USB 2.0
applications."

The other one (PRTR5V0U2F) is 1 pF from I/O to ground.

Cheers

Phil Hobbs

Mike Monett VE3BTI

2023-01-30 09:22:17 UTC

Post by Phil Hobbs
The other one (PRTR5V0U2F) is 1 pF from I/O to ground.
Cheers
Phil Hobbs

That's what I wrote. Quote:

So what do IC's use for ESD protection? I don't know, but I suspect it is
reverse-biased diodes to VCC and GND, similar to the PRTR5V0U2F, at

https://assets.nexperia.com/documents/data-sheet/PRTR5V0U2F_PRTR5V0U2K.pdf

The waveforms on Page 6, Fig 4. ESD clamping test setup and waveforms, show
very significant reduction in ESD amplitudes, from 800V peak to 20V peak.

In addition, the low capacitance of 1 pF enables their use in higher speed
USB applications. Cheaper and much better performance than the 75240.

However, I wonder if it is really needed, since many ICs are already rated
for ESD protection up to 8 kV.

--
MRM

John Larkin

2023-01-30 15:34:12 UTC

On Mon, 30 Jan 2023 09:22:17 -0000 (UTC), Mike Monett VE3BTI

Post by Phil Hobbs
The other one (PRTR5V0U2F) is 1 pF from I/O to ground.
Cheers
Phil Hobbs

So what do IC's use for ESD protection? I don't know, but I suspect it is
reverse-biased diodes to VCC and GND, similar to the PRTR5V0U2F, at
https://assets.nexperia.com/documents/data-sheet/PRTR5V0U2F_PRTR5V0U2K.pdf
The waveforms on Page 6, Fig 4. ESD clamping test setup and waveforms, show
very significant reduction in ESD amplitudes, from 800V peak to 20V peak.
In addition, the low capacitance of 1 pF enables their use in higher speed
USB applications. Cheaper and much better performance than the 75240.
However, I wonder if it is really needed, since many ICs are already rated
for ESD protection up to 8 kV.

I've used 8-channel analog multiplexers purely for their ESD diodes.

Clifford Heath

2023-01-30 04:09:15 UTC

Post by Lasse Langwadt Christensen
it sorta works like a zener diode
http://youtu.be/BGcKjy_UNQ4

That circuit has a big advantage. The capacitance of a
reverse-biased BE
junction is very low, so it should be much faster than a Zener.

There are USB ESD protectors that are much, much better.
Cheers
Phil Hobbs

Any links?

The ones we've used are
IC TVS 2X USB ESD DIODES+ZENER 5.5V XSON-6 PRTR5V0U2F,115

In-between those two, I have used SRV05-4L.

It looks like it's my news service/client that's wonky; apologies Lasse.

CH

piglet

2023-01-29 16:00:49 UTC

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

I never said it was appropriately used in that circuit! Probably
designed by a physics student who thought it looked clever?

piglet

John Walliker

2023-01-29 16:15:38 UTC

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

I never said it was appropriately used in that circuit! Probably
designed by a physics student who thought it looked clever?
piglet

It was probably intended to protect the person or animal to which the electrodes
are connected from being injured by excessive dc in the event of a failure of
one of the other components. I'm assuming it was intended as an ECG
or EMG amplifier.

John

Fred Bloggs

2023-01-29 17:42:39 UTC

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

I never said it was appropriately used in that circuit! Probably
designed by a physics student who thought it looked clever?

Biomedical research by pros.

Post by piglet
piglet

Ricky

2023-01-29 18:06:19 UTC

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

I never said it was appropriately used in that circuit! Probably
designed by a physics student who thought it looked clever?
piglet

The problem with diodes to the power rails, is that it injects current into those rails. This circuit dumps the bulk of the energy into ground and the diode clamps deal with the rest. Looks like a good circuit to me. Amplifier inputs are not always about minimizing input capacitance. Only optimize what needs to be optimized. You save a lot of work and the design is more widely useful.

--
Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

Fred Bloggs

2023-01-29 17:41:54 UTC

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

https://pubmed.ncbi.nlm.nih.gov/16594298/

John Larkin

2023-01-29 18:18:14 UTC

On Sun, 29 Jan 2023 09:41:54 -0800 (PST), Fred Bloggs

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

https://pubmed.ncbi.nlm.nih.gov/16594298/

$40 to see the PDF. No thanks.

Ricky

2023-01-29 18:26:28 UTC

Post by John Larkin
On Sun, 29 Jan 2023 09:41:54 -0800 (PST), Fred Bloggs

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

https://pubmed.ncbi.nlm.nih.gov/16594298/

$40 to see the PDF. No thanks.

https://www.academia.edu/5202695/Increased_Power_Line_Interference_Rejection_by_a_Stray_Capacitance_Drive?email_work_card=view-paper

--
Rick C.

--- Get 1,000 miles of free Supercharging
--- Tesla referral code - https://ts.la/richard11209

Ricky

2023-01-29 18:21:43 UTC

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

https://pubmed.ncbi.nlm.nih.gov/16594298/

You have the same guy, but this is the paper the circuit I posted came from. I was able to download the PDF file.

https://www.academia.edu/5202695/Increased_Power_Line_Interference_Rejection_by_a_Stray_Capacitance_Drive?email_work_card=view-paper

You may have to select it before you try to open the link since it is a bit long.

--
Rick C.

+- Get 1,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209

Fred Bloggs

2023-01-29 20:11:26 UTC

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

I'm pretty sure the BAVs are there for ESD protection. Now the hunt is on for the rationale behind BC850 clamp.

Lasse Langwadt Christensen

2023-01-29 20:29:54 UTC

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

I'm pretty sure the BAVs are there for ESD protection. Now the hunt is on for the rationale behind BC850 clamp.

it works like a zener, together with the 5.1k it limits how much current can be pushed into the supply

Fred Bloggs

2023-01-29 20:33:26 UTC

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

I'm pretty sure the BAVs are there for ESD protection. Now the hunt is on for the rationale behind BC850 clamp.

it works like a zener, together with the 5.1k it limits how much current can be pushed into the supply

Possible but not likely. It's there for offset reduction/ elimination.

Fred Bloggs

2023-01-29 20:43:55 UTC

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

I'm pretty sure the BAVs are there for ESD protection. Now the hunt is on for the rationale behind BC850 clamp.

it works like a zener, together with the 5.1k it limits how much current can be pushed into the supply

The output difference signal is AC coupled, so a little bit of offset is okay. They just need to keep the offset well away from rail'ing the OAs.

John Walliker

2023-01-29 23:20:40 UTC

Post by John Larkin
That's a really weird circuit.

I'm pretty sure the BAVs are there for ESD protection. Now the hunt is on for the rationale behind BC850 clamp.

The BC850 clamps in conjunction with the 22k input resistors are almost certainly there
to protect the patient from excessive dc under single fault conditions. Direct current
flowing through electrodes attached to the skin can cause severe burns if it is sustained
for a long time - which could easily happen in some medical situations.
Nobody would put 22k resistors in series with the input of a low-noise amplifier if
they didn't need to. Their purpose is to limit the current that can flow when driven by the clamping
voltage. Without the clamps the fault current through the electrodes would be around
10 times greater if, for example, one of the BAV99s developed a short to Vcc.

John

Lasse Langwadt Christensen

2023-01-29 23:59:01 UTC

Post by John Larkin
That's a really weird circuit.

I'm pretty sure the BAVs are there for ESD protection. Now the hunt is on for the rationale behind BC850 clamp.

the opamps are only rated for a total supply of 5.5V which it about where the transistor would clamp
so that wouldn't do much

Fred Bloggs

2023-01-30 17:58:02 UTC

Post by John Larkin
That's a really weird circuit.

I'm pretty sure the BAVs are there for ESD protection. Now the hunt is on for the rationale behind BC850 clamp.

The circuit runs off 1.8V battery power.

John Walliker

2023-01-30 18:34:04 UTC

Post by John Larkin
That's a really weird circuit.

I'm pretty sure the BAVs are there for ESD protection. Now the hunt is on for the rationale behind BC850 clamp.

The circuit runs off 1.8V battery power.

Where is that stated on the schematic that Ricky originally posted?

John

Fred Bloggs

2023-01-30 18:50:22 UTC

Post by John Larkin
That's a really weird circuit.

I'm pretty sure the BAVs are there for ESD protection. Now the hunt is on for the rationale behind BC850 clamp.

The circuit runs off 1.8V battery power.

Where is that stated on the schematic that Ricky originally posted?
John

Where on that schematic does it say it was anything else? Or even line powered?

John Walliker

2023-01-30 19:44:47 UTC

Post by John Larkin
That's a really weird circuit.

I'm pretty sure the BAVs are there for ESD protection. Now the hunt is on for the rationale behind BC850 clamp.

The circuit runs off 1.8V battery power.

Where is that stated on the schematic that Ricky originally posted?
John

Where on that schematic does it say it was anything else? Or even line powered?

So we are all trying to guess the answer based on insufficient information.
Regardless of that problem, there is a requirement to limit the maximum dc
(and ac, depending on frequency) currents that can flow through electrodes
connected to people or animals both under normal operating conditions and
in single fault conditions.
See IEC 60601 for chapter and verse.

John

Fred Bloggs

2023-01-29 20:31:51 UTC

Low leakage and lower dynamic resistance due to transistor action.
piglet

The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.
That's a really weird circuit.

Okay, you were close. The diode connected BC850 is there to divert the BAV leakage away from the OA input, which would produce a sizeable output offset with all that gain.

Ricky

2023-01-29 17:48:34 UTC