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.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
Not OT: BC850 as a diode clamp?
Started by ●January 29, 2023
Reply by ●January 29, 20232023-01-29
Reply by ●January 29, 20232023-01-29
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?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
Reply by ●January 29, 20232023-01-29
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?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.
Reply by ●January 29, 20232023-01-29
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.The non-inverting configuration is self-corrupting with CMRR.> > Horrible mess. Why not buy one good diffamp?
Reply by ●January 29, 20232023-01-29
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
Reply by ●January 29, 20232023-01-29
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 inputI 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
Reply by ●January 29, 20232023-01-29
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
Reply by ●January 29, 20232023-01-29
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.
Reply by ●January 29, 20232023-01-29
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 currentAnd 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(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
Reply by ●January 29, 20232023-01-29
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
