Not OT: BC850 as a diode clamp?...

On Sunday, January 29, 2023 at 2:18:27 PM UTC-4, John Larkin wrote:
On Sun, 29 Jan 2023 09:41:54 -0800 (PST), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

On Sunday, January 29, 2023 at 10:31:15 AM UTC-5, John Larkin wrote:
On Sun, 29 Jan 2023 10:34:43 +0000, piglet <erichp...@hotmail.com
wrote:
On 29/01/2023 05:41, Ricky wrote:
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
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.
Click to expand...

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
 
On Sunday, January 29, 2023 at 2:24:39 PM UTC-4, John Larkin wrote:
On Sun, 29 Jan 2023 09:41:41 -0800 (PST), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

On Sunday, January 29, 2023 at 1:10:30 AM UTC-5, bill....@ieee.org wrote:
On Sunday, January 29, 2023 at 4:41:49 PM UTC+11, Ricky wrote:
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
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?
Click to expand...

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
 
On Sunday, January 29, 2023 at 1:24:39 PM UTC-5, John Larkin wrote:
On Sun, 29 Jan 2023 09:41:41 -0800 (PST), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

On Sunday, January 29, 2023 at 1:10:30 AM UTC-5, bill....@ieee.org wrote:
On Sunday, January 29, 2023 at 4:41:49 PM UTC+11, Ricky wrote:
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
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?
Click to expand...

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.
 
On Sunday, January 29, 2023 at 1:24:39 PM UTC-5, John Larkin wrote:
On Sun, 29 Jan 2023 09:41:41 -0800 (PST), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

On Sunday, January 29, 2023 at 1:10:30 AM UTC-5, bill....@ieee.org wrote:
On Sunday, January 29, 2023 at 4:41:49 PM UTC+11, Ricky wrote:
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
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.
Click to expand...

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

Horrible mess. Why not buy one good diffamp?
Click to expand...
 
søndag den 29. januar 2023 kl. 19.15.22 UTC+1 skrev John Larkin:
On Sun, 29 Jan 2023 07:41:19 -0800 (PST), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

søndag den 29. januar 2023 kl. 16.31.15 UTC+1 skrev John Larkin:
On Sun, 29 Jan 2023 10:34:43 +0000, piglet <erichp...@hotmail.com
wrote:
On 29/01/2023 05:41, Ricky wrote:
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
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

https://youtu.be/BGcKjy_UNQ4?t=18

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
Click to expand...

the BAV99s are not really needed the opamp is rated for +/-10mA into the input
 
On Sunday, January 29, 2023 at 2:56:15 PM UTC-4, lang...@fonz.dk wrote:
søndag den 29. januar 2023 kl. 19.15.22 UTC+1 skrev John Larkin:
On Sun, 29 Jan 2023 07:41:19 -0800 (PST), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

søndag den 29. januar 2023 kl. 16.31.15 UTC+1 skrev John Larkin:
On Sun, 29 Jan 2023 10:34:43 +0000, piglet <erichp...@hotmail.com
wrote:
On 29/01/2023 05:41, Ricky wrote:
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
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

https://youtu.be/BGcKjy_UNQ4?t=18

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
Click to expand...

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
 
søndag den 29. januar 2023 kl. 20.04.31 UTC+1 skrev Ricky:
On Sunday, January 29, 2023 at 2:56:15 PM UTC-4, lang...@fonz.dk wrote:
søndag den 29. januar 2023 kl. 19.15.22 UTC+1 skrev John Larkin:
On Sun, 29 Jan 2023 07:41:19 -0800 (PST), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

søndag den 29. januar 2023 kl. 16.31.15 UTC+1 skrev John Larkin:
On Sun, 29 Jan 2023 10:34:43 +0000, piglet <erichp...@hotmail.com
wrote:
On 29/01/2023 05:41, Ricky wrote:
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
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

https://youtu.be/BGcKjy_UNQ4?t=18

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.
Click to expand...

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
 
On Sunday, January 29, 2023 at 10:31:15 AM UTC-5, John Larkin wrote:
On Sun, 29 Jan 2023 10:34:43 +0000, piglet <erichp...@hotmail.com
wrote:
On 29/01/2023 05:41, Ricky wrote:
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
The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.

That\'s a really weird circuit.
Click to expand...

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 wrote:
søndag den 29. januar 2023 kl. 20.04.31 UTC+1 skrev Ricky:
On Sunday, January 29, 2023 at 2:56:15 PM UTC-4, lang...@fonz.dk wrote:
søndag den 29. januar 2023 kl. 19.15.22 UTC+1 skrev John Larkin:
On Sun, 29 Jan 2023 07:41:19 -0800 (PST), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

søndag den 29. januar 2023 kl. 16.31.15 UTC+1 skrev John Larkin:
On Sun, 29 Jan 2023 10:34:43 +0000, piglet <erichp...@hotmail.com
wrote:
On 29/01/2023 05:41, Ricky wrote:
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
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

https://youtu.be/BGcKjy_UNQ4?t=18

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
Click to expand...

And much lower shunt resistance.

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
Click to expand...

(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
 
søndag den 29. januar 2023 kl. 21.11.31 UTC+1 skrev Fred Bloggs:
On Sunday, January 29, 2023 at 10:31:15 AM UTC-5, John Larkin wrote:
On Sun, 29 Jan 2023 10:34:43 +0000, piglet <erichp...@hotmail.com
wrote:
On 29/01/2023 05:41, Ricky wrote:
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
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.
Click to expand...

it works like a zener, together with the 5.1k it limits how much current can be pushed into the supply
 
On Sunday, January 29, 2023 at 10:31:15 AM UTC-5, John Larkin wrote:
On Sun, 29 Jan 2023 10:34:43 +0000, piglet <erichp...@hotmail.com
wrote:
On 29/01/2023 05:41, Ricky wrote:
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
The be-junction is in parallel with two BAV99 (? illegible) diode
junctions, so there is no leakage advantage.

That\'s a really weird circuit.
Click to expand...

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.
 
On Sunday, January 29, 2023 at 3:29:58 PM UTC-5, lang...@fonz.dk wrote:
søndag den 29. januar 2023 kl. 21.11.31 UTC+1 skrev Fred Bloggs:
On Sunday, January 29, 2023 at 10:31:15 AM UTC-5, John Larkin wrote:
On Sun, 29 Jan 2023 10:34:43 +0000, piglet <erichp...@hotmail.com
wrote:
On 29/01/2023 05:41, Ricky wrote:
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
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
Click to expand...

Possible but not likely. It\'s there for offset reduction/ elimination.
 
On Sunday, January 29, 2023 at 3:29:58 PM UTC-5, lang...@fonz.dk wrote:
søndag den 29. januar 2023 kl. 21.11.31 UTC+1 skrev Fred Bloggs:
On Sunday, January 29, 2023 at 10:31:15 AM UTC-5, John Larkin wrote:
On Sun, 29 Jan 2023 10:34:43 +0000, piglet <erichp...@hotmail.com
wrote:
On 29/01/2023 05:41, Ricky wrote:
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
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
Click to expand...

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.
 
On Sunday, January 29, 2023 at 4:06:37 PM UTC-4, lang...@fonz.dk wrote:
søndag den 29. januar 2023 kl. 20.04.31 UTC+1 skrev Ricky:
On Sunday, January 29, 2023 at 2:56:15 PM UTC-4, lang...@fonz.dk wrote:
søndag den 29. januar 2023 kl. 19.15.22 UTC+1 skrev John Larkin:
On Sun, 29 Jan 2023 07:41:19 -0800 (PST), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

søndag den 29. januar 2023 kl. 16.31.15 UTC+1 skrev John Larkin:
On Sun, 29 Jan 2023 10:34:43 +0000, piglet <erichp...@hotmail.com
wrote:
On 29/01/2023 05:41, Ricky wrote:
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
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

https://youtu.be/BGcKjy_UNQ4?t=18

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
Click to expand...

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
 
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.

--
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
 
Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:

That\'s a really weird circuit.

it sorta works like a zener diode

https://youtu.be/BGcKjy_UNQ4?t=18
Click to expand...

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
 
On 1/29/2023 4:34 PM, Phil Hobbs wrote:
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.
Click to expand...

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
 
On Sunday, 29 January 2023 at 20:11:31 UTC, Fred Bloggs wrote:

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.
Click to expand...

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
 
On 30/01/23 08:34, Phil Hobbs wrote:
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.
Click to expand...
Possibly such high-speed parts dispense with ESD diodes to reduce input
capacitance?

Clifford Heath
 
mandag den 30. januar 2023 kl. 00.34.59 UTC+1 skrev Clifford Heath:
On 30/01/23 08:34, Phil Hobbs wrote:
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?
Click to expand...

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