Imagine an NPN transistor. Ground the emitter and connect the collector to some nice positive voltage. Now pull the base negative, through a current-limiting resistor. What happens?
NPN in unusual quadrant
Started by ●September 5, 2023
Reply by ●September 5, 20232023-09-05
On 2023-09-06, John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:> Imagine an NPN transistor. Ground the emitter and connect the > collector to some nice positive voltage. > > Now pull the base negative, through a current-limiting resistor. What > happens?Nothing until you exceed the emitter base reverse breakdown (or collector base breakdown) voltage, Bitter-base is usually about 5V Behaves kind of like a zener diode and damages the transistor. -- Jasen. 🇺🇦 Слава Україні
Reply by ●September 5, 20232023-09-05
On Wed, 6 Sep 2023 00:58:11 -0000 (UTC), Jasen Betts <usenet@revmaps.no-ip.org> wrote:>On 2023-09-06, John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote: >> Imagine an NPN transistor. Ground the emitter and connect the >> collector to some nice positive voltage. >> >> Now pull the base negative, through a current-limiting resistor. What >> happens? > >Nothing until you exceed the emitter base reverse breakdown (or >collector base breakdown) voltage,Not literally nothing, but not much interesting. It gets more interesting when the base zeners.> >Bitter-base is usually about 5V > >Behaves kind of like a zener diode and damages the transistor.The base current is limited. But what happens?
Reply by ●September 5, 20232023-09-05
John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:> On Wed, 6 Sep 2023 00:58:11 -0000 (UTC), Jasen Betts > <usenet@revmaps.no-ip.org> wrote: > >> On 2023-09-06, John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote: >>> Imagine an NPN transistor. Ground the emitter and connect the >>> collector to some nice positive voltage. >>> >>> Now pull the base negative, through a current-limiting resistor. What >>> happens? >> >> Nothing until you exceed the emitter base reverse breakdown (or >> collector base breakdown) voltage, > > Not literally nothing, but not much interesting. It gets more > interesting when the base zeners. > >> >> Bitter-base is usually about 5V >> >> Behaves kind of like a zener diode and damages the transistor. > > The base current is limited. But what happens? > >Haven’t tried it, at least not on purpose, but I’d guess that when the avalanche starts, most of the electrons will get sucked up by the collector. Since it’s the electrons and not the holes that do the avalanching in silicon, that might partially suppress the avalanche. If that were true, putting a positive voltage on the collector would make the base voltage slightly more negative. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
Reply by ●September 5, 20232023-09-05
On Wed, 6 Sep 2023 02:31:04 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote: >> On Wed, 6 Sep 2023 00:58:11 -0000 (UTC), Jasen Betts >> <usenet@revmaps.no-ip.org> wrote: >> >>> On 2023-09-06, John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote: >>>> Imagine an NPN transistor. Ground the emitter and connect the >>>> collector to some nice positive voltage. >>>> >>>> Now pull the base negative, through a current-limiting resistor. What >>>> happens? >>> >>> Nothing until you exceed the emitter base reverse breakdown (or >>> collector base breakdown) voltage, >> >> Not literally nothing, but not much interesting. It gets more >> interesting when the base zeners. >> >>> >>> Bitter-base is usually about 5V >>> >>> Behaves kind of like a zener diode and damages the transistor. >> >> The base current is limited. But what happens? >> >> > >Haven�t tried it, at least not on purpose, but I�d guess that when the >avalanche starts, most of the electrons will get sucked up by the >collector. > >Since it�s the electrons and not the holes that do the avalanching in >silicon, that might partially suppress the avalanche. If that were true, >putting a positive voltage on the collector would make the base voltage >slightly more negative. > >Cheers > >Phil HobbsI'd expect that zenering fills the b-e junction with lots of carriers, and some find their way into the collector. I don't know how many. Probably a lot less than foward base current. I suppose I should try it.
Reply by ●September 6, 20232023-09-06
On Tuesday, September 5, 2023 at 5:05:16 PM UTC-7, John Larkin wrote:> Imagine an NPN transistor. Ground the emitter and connect the > collector to some nice positive voltage. > > Now pull the base negative, through a current-limiting resistor. What > happens?The collector becomes a better OFF switch; the collector breakdown Vceo applies when the base is open, but higher Vcbo applies when base is held negative.
Reply by ●September 6, 20232023-09-06
On Tue, 5 Sep 2023 21:28:06 -0700 (PDT), whit3rd <whit3rd@gmail.com> wrote:>On Tuesday, September 5, 2023 at 5:05:16?PM UTC-7, John Larkin wrote: >> Imagine an NPN transistor. Ground the emitter and connect the >> collector to some nice positive voltage. >> >> Now pull the base negative, through a current-limiting resistor. What >> happens? > >The collector becomes a better OFF switch; the collector breakdown >Vceo applies when the base is open, but higher Vcbo applies >when base is held negative.But what happens?
Reply by ●September 6, 20232023-09-06
On Tue, 05 Sep 2023 19:38:37 -0700, John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote: <snip>> >I suppose I should try it.? ? ? RL
Reply by ●September 6, 20232023-09-06
On 06/09/2023 01:04, John Larkin wrote:> Imagine an NPN transistor. Ground the emitter and connect the > collector to some nice positive voltage. > > Now pull the base negative, through a current-limiting resistor. What > happens? >If the collector is already positive and pullup resistor is not extremely high then I think not much detectable will happen even once the Veb junction breaks down. But if the collector is open circuit or very lightly loaded then the collector should show that photo-electric effect "the pease conundrum" we discussed back in 2015. Whereby the E-B avalanching junction emits light that the C-B junction does a photo-diode act on? piglet
Reply by ●September 6, 20232023-09-06
On Wed, 6 Sep 2023 19:19:20 +0100, piglet <erichpwagner@hotmail.com> wrote:>On 06/09/2023 01:04, John Larkin wrote: >> Imagine an NPN transistor. Ground the emitter and connect the >> collector to some nice positive voltage. >> >> Now pull the base negative, through a current-limiting resistor. What >> happens? >> > >If the collector is already positiveThat was a stated condition>and pullup resistor is not >extremely high then I think not much detectable will happen even once >the Veb junction breaks down."Detectable" can include amps or picoamps of currents. Curious that nobody seems to address this case.
