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 -- 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
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.jpgIt 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
Reply by ●January 29, 20232023-01-29
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
Reply by ●January 29, 20232023-01-29
Am 29.01.23 um 11:34 schrieb piglet:> 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 >Someone at NIST built a complete ring mixer around that structure. < https://tf.nist.gov/general/pdf/2556.pdf > Gerhard
Reply by ●January 29, 20232023-01-29
Gerhard Hoffmann <dk4xp@arcor.de> wrote:> Someone at NIST built a complete ring mixer around that structure. > > < https://tf.nist.gov/general/pdf/2556.pdf > > > Gerhard >+1. Thanks -- MRM
Reply by ●January 29, 20232023-01-29
On Sun, 29 Jan 2023 10:34:43 +0000, piglet <erichpwagner@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. > >pigletThe be-junction is in parallel with two BAV99 (? illegible) diode junctions, so there is no leakage advantage. That's a really weird circuit.
Reply by ●January 29, 20232023-01-29
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
Reply by ●January 29, 20232023-01-29
On 29/01/2023 15:31, John Larkin wrote:> On Sun, 29 Jan 2023 10:34:43 +0000, piglet <erichpwagner@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 never said it was appropriately used in that circuit! Probably designed by a physics student who thought it looked clever? piglet
Reply by ●January 29, 20232023-01-29
On Sunday, 29 January 2023 at 16:00:56 UTC, erichp...@hotmail.com wrote:> On 29/01/2023 15:31, 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 never said it was appropriately used in that circuit! Probably > designed by a physics student who thought it looked clever? > > pigletIt 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
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.https://pubmed.ncbi.nlm.nih.gov/16594298/
