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.
BJT E-B zener
Started by ●February 28, 2023
Reply by ●February 28, 20232023-02-28
neo5bass 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.<https://wiki.analog.com/university/courses/electronics/electronics-lab-3> Danke, -- Don, KB7RPU, https://www.qsl.net/kb7rpu There was a young lady named Bright Whose speed was far faster than light; She set out one day In a relative way And returned on the previous night.
Reply by ●February 28, 20232023-02-28
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 + | --- 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.
Reply by ●February 28, 20232023-02-28
On Tue, 28 Feb 2023 07:05:54 -0800 (PST), "neo5...@gmail.com" <neo5bass@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.A 2n3904 b-e should be a stable zener, good for the transistor's normal dissipation. Long-term zenering will wreck the transistor-mode beta but is otherwise pretty stable. The b-e junction is small compared to a regular zener, so has less capacitance. Keep the current low. Some npn transistors can be used backwards (c-e, collector negative) as "reference diodes." The forward biased c-b junction is in series with the zenering b-e junction and the temperature coefficients cancel, around 6.8 volts as I recall. 1N821 does this dual-junction tempco trick. These sorts of things typically have some current where the tempco is zero. But cheap bandgap references have made the transistor tricks mostly history.
Reply by ●February 28, 20232023-02-28
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 > > > + > | > --- 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.But that's not a zener.
Reply by ●February 28, 20232023-02-28
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" <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 > > > + > | > --- 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... Arie
Reply by ●February 28, 20232023-02-28
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 >> >> >> + >> | >> --- 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. > >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 :-)
Reply by ●February 28, 20232023-02-28
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 >>> >>> >>> + >>> | >>> --- 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. >> >>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.
Reply by ●February 28, 20232023-02-28
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.
Reply by ●February 28, 20232023-02-28
On Tue, 28 Feb 2023 09:53:19 -0800 (PST), Fred Bloggs <bloggs.fredbloggs.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"
