On Tuesday, February 28, 2023 at 1:09:51 PM UTC-5, John Larkin wrote:> On Tue, 28 Feb 2023 09:53:19 -0800 (PST), Fred Bloggs > <bloggs.fred...@gmail.com> wrote: > >On Tuesday, February 28, 2023 at 10:05:59?AM UTC-5, neo5...@gmail.com wrote: > >> Where would I go to look for information about using the E-B connection of a 2N3904 as a zener? It has much better leakage than a regular zener but I dont know what kind of power it can handle or how stable it is when used this way. > > > > > >The biggest problem is uncertainty in the zener voltage, as in BIG uncertainty. Real zeners are very accurate in that respect, and they have negligible leakage ( uAmps ) for voltages less than 80% zener voltage. Sounds like you want to use it as a clamp if you're concerned about off state leakage. > That's reversed. Lower voltage breakdown diodes, "real zeners", use a > tunneling effect and have soft knees. Higher voltage parts, > technically avalanche diodes, have sharp knees and low current just > below breakdown. They have opposite tempcos. The fuzzy boundary > between types is roughly 6 volts. > > A 10 or so volt avalanche diode can have nA current just below > breakdown voltage. They do fun stuff at low currents too. > > Nowadays people call both kinds "zeners"Right- the transistor will be an avalanche breakdown. Another drawback of the double junction conduction you mentioned is the requirement of minimum current to keep it going, otherwise you build an oscillator if the external circuit is right. That 3904 has an abs max for veb of 6V, so it could easily take 12V before it breaks down. It's unusable except in applications that don't require much precision.
BJT E-B zener
Started by ●February 28, 2023
Reply by ●February 28, 20232023-02-28
Reply by ●February 28, 20232023-02-28
On Tuesday, February 28, 2023 at 11:00:21 AM UTC-5, Arie de Muijnck wrote:> On 2023-02-28 16:48, Jan Panteltje wrote: > > On a sunny day (Tue, 28 Feb 2023 07:05:54 -0800 (PST)) it happened > > "neo5...@gmail.com" <neo5...@gmail.com> wrote in > > <2728e43f-ea4f-4df3...@googlegroups.com>: > > > >> Where would I go to look for information about using the E-B connection of a 2N3904 as a zener? It has much better leakage than > >> a regular zener but I dont know what kind of power it can handle or how stable it is when used this way. > > > > If you connect the collector to the base as well, > > the thing can take more current > > > > > > + > > | > > --- c > > | > > --b > > e > > | > > - > > > > Now 200 mA Imax collector current counts, zenering about .7 V gives .7 * .2 = .140 mW > > Note that Vbe sat may be as high as .95 V at 90 mA Ic, even higher at > > Also Vbe is very temperature dependent. > > See datasheet. > > If you want a precise voltage better use something else. > > > > A big Si diode used in forward direction will give the same effect, voltage drop and temperature problems. > Let's assume the OP wants to use the BE junction as a zener, not as forward diode... > > ArieNope E-B Zener of around 7V or so.
Reply by ●February 28, 20232023-02-28
Reply by ●February 28, 20232023-02-28
On Tuesday, February 28, 2023 at 12:53:23 PM UTC-5, Fred Bloggs wrote:> On Tuesday, February 28, 2023 at 10:05:59 AM UTC-5, neo5...@gmail.com wrote: > > Where would I go to look for information about using the E-B connection of a 2N3904 as a zener? It has much better leakage than a regular zener but I dont know what kind of power it can handle or how stable it is when used this way. > The biggest problem is uncertainty in the zener voltage, as in BIG uncertainty. Real zeners are very accurate in that respect, and they have negligible leakage ( uAmps ) for voltages less than 80% zener voltage. Sounds like you want to use it as a clamp if you're concerned about off state leakage.Exactly right. Clamping the output of a 33V TVS with as little leakage as possible. The E-B Zener has very low leakage until it goes into breakdown but lowers the overall Vin at that point so I can clamp it more tightly just below 5 for my ADC input. In my case I'm looking for a overall error of less than 10 to 20nA leakage from my protection circuit because this device will be able to see -50mV to 5.000V of valid signals though not all at once. The leakage of a regular zener is simply too high for this to work.
Reply by ●February 28, 20232023-02-28
On 28.02.23 21:33, Lasse Langwadt Christensen wrote:> https://youxxxxxxxjy_UNQ4 >whatever are people thinking when communicating with unexplained web links? I ignore them all.
Reply by ●February 28, 20232023-02-28
On Tue, 28 Feb 2023 12:37:51 -0800 (PST), "neo5...@gmail.com" <neo5bass@gmail.com> wrote:>On Tuesday, February 28, 2023 at 12:53:23?PM UTC-5, Fred Bloggs wrote: >> On Tuesday, February 28, 2023 at 10:05:59?AM UTC-5, neo5...@gmail.com wrote: >> > Where would I go to look for information about using the E-B connection of a 2N3904 as a zener? It has much better leakage than a regular zener but I dont know what kind of power it can handle or how stable it is when used this way. >> The biggest problem is uncertainty in the zener voltage, as in BIG uncertainty. Real zeners are very accurate in that respect, and they have negligible leakage ( uAmps ) for voltages less than 80% zener voltage. Sounds like you want to use it as a clamp if you're concerned about off state leakage. > >Exactly right. Clamping the output of a 33V TVS with as little leakage as possible. The E-B Zener has very low leakage until it goes into breakdown but lowers the overall Vin at that point so I can clamp it more tightly just below 5 for my ADC input. In my case I'm looking for a overall error of less than 10 to 20nA leakage from my protection circuit because this device will be able to see -50mV to 5.000V of valid signals though not all at once. The leakage of a regular zener is simply too high for this to work.You might use two official diodes to clamp to some power supply and ground. Transistor c-b junctions make excellent low-leakage diodes, pA or for some parts fA reverse leakage. Official diodes, like 1N914 types, tend to be leaky and photosensitive. The PAD series of "low leakage" diodes are terrible. The sadly departed BFT25 made a great diode. I measured about 10 fA leakage, but that was about my measurement resolution. I sometimes use depletion fets as the "resistor" in a clamp circuit. See AoE3 fig 5.80. Are TVS diodes leaky? I never tested for that.
Reply by ●February 28, 20232023-02-28
On 2023-02-28 16:57, John Larkin wrote:> On Tue, 28 Feb 2023 12:37:51 -0800 (PST), "neo5...@gmail.com" > <neo5bass@gmail.com> wrote: > >> On Tuesday, February 28, 2023 at 12:53:23?PM UTC-5, Fred Bloggs wrote: >>> On Tuesday, February 28, 2023 at 10:05:59?AM UTC-5, neo5...@gmail.com wrote: >>>> Where would I go to look for information about using the E-B connection of a 2N3904 as a zener? It has much better leakage than a regular zener but I dont know what kind of power it can handle or how stable it is when used this way. >>> The biggest problem is uncertainty in the zener voltage, as in BIG uncertainty. Real zeners are very accurate in that respect, and they have negligible leakage ( uAmps ) for voltages less than 80% zener voltage. Sounds like you want to use it as a clamp if you're concerned about off state leakage. >> >> Exactly right. Clamping the output of a 33V TVS with as little leakage as possible. The E-B Zener has very low leakage until it goes into breakdown but lowers the overall Vin at that point so I can clamp it more tightly just below 5 for my ADC input. In my case I'm looking for a overall error of less than 10 to 20nA leakage from my protection circuit because this device will be able to see -50mV to 5.000V of valid signals though not all at once. The leakage of a regular zener is simply too high for this to work. > > You might use two official diodes to clamp to some power supply and > ground. Transistor c-b junctions make excellent low-leakage diodes, pA > or for some parts fA reverse leakage. Official diodes, like 1N914 > types, tend to be leaky and photosensitive. > > The PAD series of "low leakage" diodes are terrible. > > The sadly departed BFT25 made a great diode. I measured about 10 fA > leakage, but that was about my measurement resolution. > > I sometimes use depletion fets as the "resistor" in a clamp circuit. > See AoE3 fig 5.80. > > Are TVS diodes leaky? I never tested for that. >There are USB protectors that work pretty well for that, e.g. PRTR5V0U2. You can get it in SOT-143 (a four-pin SOT23), which is convenient. It has a zener plus two pairs of Schottkys. 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 ●February 28, 20232023-02-28
On Tue, 28 Feb 2023 17:07:02 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 2023-02-28 16:57, John Larkin wrote: >> On Tue, 28 Feb 2023 12:37:51 -0800 (PST), "neo5...@gmail.com" >> <neo5bass@gmail.com> wrote: >> >>> On Tuesday, February 28, 2023 at 12:53:23?PM UTC-5, Fred Bloggs wrote: >>>> On Tuesday, February 28, 2023 at 10:05:59?AM UTC-5, neo5...@gmail.com wrote: >>>>> Where would I go to look for information about using the E-B connection of a 2N3904 as a zener? It has much better leakage than a regular zener but I dont know what kind of power it can handle or how stable it is when used this way. >>>> The biggest problem is uncertainty in the zener voltage, as in BIG uncertainty. Real zeners are very accurate in that respect, and they have negligible leakage ( uAmps ) for voltages less than 80% zener voltage. Sounds like you want to use it as a clamp if you're concerned about off state leakage. >>> >>> Exactly right. Clamping the output of a 33V TVS with as little leakage as possible. The E-B Zener has very low leakage until it goes into breakdown but lowers the overall Vin at that point so I can clamp it more tightly just below 5 for my ADC input. In my case I'm looking for a overall error of less than 10 to 20nA leakage from my protection circuit because this device will be able to see -50mV to 5.000V of valid signals though not all at once. The leakage of a regular zener is simply too high for this to work. >> >> You might use two official diodes to clamp to some power supply and >> ground. Transistor c-b junctions make excellent low-leakage diodes, pA >> or for some parts fA reverse leakage. Official diodes, like 1N914 >> types, tend to be leaky and photosensitive. >> >> The PAD series of "low leakage" diodes are terrible. >> >> The sadly departed BFT25 made a great diode. I measured about 10 fA >> leakage, but that was about my measurement resolution. >> >> I sometimes use depletion fets as the "resistor" in a clamp circuit. >> See AoE3 fig 5.80. >> >> Are TVS diodes leaky? I never tested for that. >> > >There are USB protectors that work pretty well for that, e.g. PRTR5V0U2. > You can get it in SOT-143 (a four-pin SOT23), which is convenient. > >It has a zener plus two pairs of Schottkys. > >Cheers > >Phil HobbsInteresting part. The diodes are < 1 nA leakage typ.
Reply by ●February 28, 20232023-02-28
On Wednesday, March 1, 2023 at 6:08:18 AM UTC+11, Fred Bloggs wrote:> On Tuesday, February 28, 2023 at 1:09:51 PM UTC-5, John Larkin wrote: > > On Tue, 28 Feb 2023 09:53:19 -0800 (PST), Fred Bloggs > > <bloggs.fred...@gmail.com> wrote: > > >On Tuesday, February 28, 2023 at 10:05:59?AM UTC-5, neo5...@gmail.com wrote: > > >> Where would I go to look for information about using the E-B connection of a 2N3904 as a zener? It has much better leakage than a regular zener but I dont know what kind of power it can handle or how stable it is when used this way. > > > > > > > > >The biggest problem is uncertainty in the zener voltage, as in BIG uncertainty. Real zeners are very accurate in that respect, and they have negligible leakage ( uAmps ) for voltages less than 80% zener voltage. Sounds like you want to use it as a clamp if you're concerned about off state leakage. > > That's reversed. Lower voltage breakdown diodes, "real zeners", use a > > tunneling effect and have soft knees. Higher voltage parts, > > technically avalanche diodes, have sharp knees and low current just > > below breakdown. They have opposite tempcos. The fuzzy boundary > > between types is roughly 6 volts. > > > > A 10 or so volt avalanche diode can have nA current just below > > breakdown voltage. They do fun stuff at low currents too. > > > > Nowadays people call both kinds "zeners"> Right- the transistor will be an avalanche breakdown.Actually, it will be siting in the overlap region between the Zener mechanism and the avalanche region.> Another drawback of the double junction conduction you mentioned is the requirement of minimum current to keep it going, otherwise you build an oscillator if the external circuit is right. That 3904 has an abs max for veb of 6V, so it could easily take 12V before it breaks down. It's unusable except in applications that don't require much precision.Rubbish. Back in the 1960's the British Journal of Scientific Instruments - now Measurement Science and Technology - published a paper on using a gold-doped switching transistor as a cheap alternative to the 1N821 - 1N829 series. You had to tune the forward current in the 1ma to 5mA range to get a precisely zero temperature coefficient, but it gave you a very stable reference voltage close to 6.2V. The 1N821 series have a nominally zero temperature coefficient at 7.5mA, but the selection process that picks are the premium 1N829 part just picks the parts where the zero happens at close to 7.5mA. The stable breakdown voltage range is 5.9V to 6.5V - +/-5% - even for the 1N829, and you have to calibrate that out. -- Bill Sloman, Sydney
Reply by ●March 1, 20232023-03-01
On a sunny day (Tue, 28 Feb 2023 08:45:28 -0800) it happened John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote in <gpbsvhl4gjtjc4ra4mcsobat1ii2m7leub@4ax.com>:>On Tue, 28 Feb 2023 16:33:40 GMT, Jan Panteltje <alien@comet.invalid> >wrote: > >>On a sunny day (Tue, 28 Feb 2023 08:00:50 -0800) it happened John Larkin >><jlarkin@highlandSNIPMEtechnology.com> wrote in >><j89svh5rd7a465i52hob4t601cod04h4p9@4ax.com>: >> >>>On Tue, 28 Feb 2023 15:48:10 GMT, Jan Panteltje <alien@comet.invalid> >>>wrote: >>> >>>>On a sunny day (Tue, 28 Feb 2023 07:05:54 -0800 (PST)) it happened >>>>"neo5...@gmail.com" <neo5bass@gmail.com> wrote in >>>><2728e43f-ea4f-4df3-b8e1-68b4a76e907dn@googlegroups.com>: >>>> >>>>>Where would I go to look for information about using the E-B connection of a 2N3904 as a zener? It has much better leakage >>>>>than >>>>>a regular zener but I dont know what kind of power it can handle or how stable it is when used this way. >>>> >>>>If you connect the collector to the base as well, >>>>the thing can take more current >>>> >>>> >>>> - >>>> >>>>Now 200 mA Imax collector current counts, zenering about .7 V gives .7 * .2 = .140 mW >>>>Note that Vbe sat may be as high as .95 V at 90 mA Ic, even higher at >>>>Also Vbe is very temperature dependent. >>>>See datasheet. >>>>If you want a precise voltage better use something else. >>>> >>>>A big Si diode used in forward direction will give the same effect, voltage drop and temperature problems. >>> >>>But that's not a zener. >> >> >>Ah, seems he wants it reverse biased, my error. >>Using the thing that way may cause it to die after a while :-) > >It would be an interesting experiment to measure the b-e zener voltage >long-term, at a couple of currents. Beta degrades in a transistor if >the base is zenered, so something is going on.I remember reading something about 'ectromigration', so chemical changes on the chip due to applied voltages. In the example I gave with the be junction in forward direction you can make it limit at any voltage you want by just adding 2 resistors: + | |----c | R1 | |---b si NPN | R2 | |--- e | - Vbe multiplier But indeed there are very good zeners around at the 5.something voltage range. Else use a TL431, should still be available.. Much more stable.
