On a sunny day (Fri, 3 Mar 2023 11:01:43 +0100) it happened Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote in <ttsgi6$jssm$1@dont-email.me>:>On 02-03-2023 22:33, Anthony William Sloman wrote: >> On Friday, March 3, 2023 at 8:06:17 AM UTC+11, John Larkin wrote: >>> On Thu, 2 Mar 2023 09:07:43 -0800 (PST), whit3rd <whi...@gmail.com> >>> wrote: >>>> On Tuesday, February 28, 2023 at 7:05:59?AM UTC-8, 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 'much better leakage' relates to test protocols, more than reality. The recommendation to >>>> use a 2N3904 as a reference goes back to National Semiconductor's (now TI) process for making those; >>>> the Motorola (now ONsemi) process might be different (and breakdown is only specified as 'over 6.0V'). >>>> >>>> E-B breakdown also applies the opposite to 'normal' field on the surface of the >>>> transistor, where the B and E contacts are made; such surfaces are passivated, but >>>> field reversal can move dirt on the surface to age the component abnormally. >>>> >>>> So, no one knows 'how stable it is' for this usage, unless they've time/temperature >>>> tested a few batches from a known process and the manufacturer doesn't change anything. >>>> That '2N3904' part number was defined many decades ago, there have been lots >>>> of variant parts holding to that loose specification, sold under that part number. >>>> >>>> It'll probably work. That doesn't mean it's good design practice to depend on it. >>> >>> You can get a 0.5% bandgap voltage reference for 4 cents. >> >> But John Larkin doesn't know the part number. H's probably thinking of the LM4040 >> >> >> https://www.ti.com/lit/ds/symlink/lm4040-n.pdf?HQS=dis-mous-null-mousermode-dsf-pf-null-wwe&ts=1677716796343&ref_url=https%253A%252F%252Fwww.mouser.jp%252F >> >> but that is lot more expensive than 4 cents - $1.37 even in thousands. >> > >6 cents: > >https://www.avnet.com/shop/us/products/diodes-inc/az431lantr-e1-3074457345625002718?CMP=EMA_FindChips_inventoryfeed_VSELM317 with adjust to ground is 1.2V bandgap Or any other voltage you like up to 37 V https://nl.aliexpress.com/item/32848278588.html Almost for free I always have some around.
BJT E-B zener
Started by ●February 28, 2023
Reply by ●March 3, 20232023-03-03
Reply by ●March 3, 20232023-03-03
On Friday, March 3, 2023 at 9:52:14 PM UTC+11, Jan Panteltje wrote:> On a sunny day (Fri, 3 Mar 2023 11:01:43 +0100) it happened Klaus Vestergaard > Kragelund <klau...@hotmail.com> wrote in <ttsgi6$jssm$1...@dont-email.me>: > >On 02-03-2023 22:33, Anthony William Sloman wrote: > >> On Friday, March 3, 2023 at 8:06:17â ¯AM UTC+11, John Larkin wrote: > >>> On Thu, 2 Mar 2023 09:07:43 -0800 (PST), whit3rd <whi...@gmail.com> > >>> wrote: > >>>> On Tuesday, February 28, 2023 at 7:05:59?AM UTC-8, 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 'much better leakage' relates to test protocols, more than reality. The recommendation to > >>>> use a 2N3904 as a reference goes back to National Semiconductor's (now TI) process for making those; > >>>> the Motorola (now ONsemi) process might be different (and breakdown is only specified as 'over 6.0V'). > >>>> > >>>> E-B breakdown also applies the opposite to 'normal' field on the surface of the > >>>> transistor, where the B and E contacts are made; such surfaces are passivated, but > >>>> field reversal can move dirt on the surface to age the component abnormally. > >>>> > >>>> So, no one knows 'how stable it is' for this usage, unless they've time/temperature > >>>> tested a few batches from a known process and the manufacturer doesn't change anything. > >>>> That '2N3904' part number was defined many decades ago, there have been lots > >>>> of variant parts holding to that loose specification, sold under that part number. > >>>> > >>>> It'll probably work. That doesn't mean it's good design practice to depend on it. > >>> > >>> You can get a 0.5% bandgap voltage reference for 4 cents. > >> > >> But John Larkin doesn't know the part number. H's probably thinking of the LM4040 > >> > >> > >> https://www.ti.com/lit/ds/symlink/lm4040-n.pdf?HQS=dis-mous-null-mousermode-dsf-pf-null-wwe&ts=1677716796343&ref_url=https%253A%252F%252Fwww.mouser.jp%252F > >> > >> but that is lot more expensive than 4 cents - $1.37 even in thousands. > > > >6 cents: > > > >https://www.avnet.com/shop/us/products/diodes-inc/az431lantr-e1-3074457345625002718?CMP=EMA_FindChips_inventoryfeed_VSE > LM317 with adjust to ground is 1.2V bandgap > Or any other voltage you like up to 37 V > https://nl.aliexpress.com/item/32848278588.html > Almost for free > I always have some around.Not exactly precision references, but Jan Panteltje and John Larkin don't go in for precision. -- Bill Sloman, Sydney
Reply by ●March 3, 20232023-03-03
On a sunny day (Fri, 3 Mar 2023 03:18:22 -0800 (PST)) it happened Anthony William Sloman <bill.sloman@ieee.org> wrote in <196fe320-7d36-4056-9574-d0b82078ea59n@googlegroups.com>:>On Friday, March 3, 2023 at 9:52:14=E2=80=AFPM UTC+11, Jan Panteltje wrote: >> On a sunny day (Fri, 3 Mar 2023 11:01:43 +0100) it happened Klaus Vestergaard >> >Kragelund <klau...@hotmail.com> wrote in <ttsgi6$jssm$1...@dont-email.me>: >> >>On 02-03-2023 22:33, Anthony William Sloman wrote: >> >> On Friday, March 3, 2023 at 8:06:17=C3=A2 =C2=AFAM UTC+11, John Larkin >wrote: >> >>> On Thu, 2 Mar 2023 09:07:43 -0800 (PST), whit3rd <whi...@gmail.com> >> >>>> wrote: >> >>>> On Tuesday, February 28, 2023 at 7:05:59?AM UTC-8, 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 'much better leakage' relates to test protocols, more than reality. >The recommendation to >> >>>> use a 2N3904 as a reference goes back to National Semiconductor's (now >TI) process for making those; >> >>>> the Motorola (now ONsemi) process might be different (and breakdown is >only specified as 'over 6.0V'). >> >>>> >> >>>> E-B breakdown also applies the opposite to 'normal' field on the surface >of the >> >>>> transistor, where the B and E contacts are made; such surfaces are passivated, >but >> >>>> field reversal can move dirt on the surface to age the component abnormally. >> >>>>> >> >>>> So, no one knows 'how stable it is' for this usage, unless they've time/temperature >> >>>>> tested a few batches from a known process and the manufacturer doesn't >change anything. >> >>>> That '2N3904' part number was defined many decades ago, there have been >lots >> >>>> of variant parts holding to that loose specification, sold under that >part number. >> >>>> >> >>>> It'll probably work. That doesn't mean it's good design practice to depend >on it. >> >>> >> >>> You can get a 0.5% bandgap voltage reference for 4 cents. >> >> >> >> But John Larkin doesn't know the part number. H's probably thinking of >the LM4040 >> >> >> >> >> >> >> >> https://www.ti.com/lit/ds/symlink/lm4040-n.pdf?HQS=3Ddis-mous-null-mousermode-dsf-pf-null-wwe&ts=3D1677716796343&ref_url=3Dhttps%253A%252F%252Fwww.mouser.jp%252F >> >>> >> >> but that is lot more expensive than 4 cents - $1.37 even in thousands. >> >> >> >6 cents: >> > >> >https://www.avnet.com/shop/us/products/diodes-inc/az431lantr-e1-3074457345625002718?CMP=3DEMA_FindChips_inventoryfeed_VSE >> >LM317 with adjust to ground is 1.2V bandgap >> Or any other voltage you like up to 37 V >> https://nl.aliexpress.com/item/32848278588.html >> Almost for free >> I always have some around. > >Not exactly precision references, but Jan Panteltje and John Larkin don't go >in for precision.The advantage of LM317 is that you can use a trimpot or resistors to set it quite close to where you want it. I often use 2 resistors in series, a big one and a smaller one for calibration. And it can deliver a LOT of current and has proven very reliable over the years and is still around since 1976 https://en.wikipedia.org/wiki/LM317
Reply by ●March 3, 20232023-03-03
On Friday, March 3, 2023 at 10:35:48 PM UTC+11, Jan Panteltje wrote:> On a sunny day (Fri, 3 Mar 2023 03:18:22 -0800 (PST)) it happened Anthony > William Sloman <bill....@ieee.org> wrote in > <196fe320-7d36-4056...@googlegroups.com>: > >On Friday, March 3, 2023 at 9:52:14=E2=80=AFPM UTC+11, Jan Panteltje wrote: > >> On a sunny day (Fri, 3 Mar 2023 11:01:43 +0100) it happened Klaus Vestergaard > >> > >Kragelund <klau...@hotmail.com> wrote in <ttsgi6$jssm$1...@dont-email.me>: > >> > >>On 02-03-2023 22:33, Anthony William Sloman wrote: > >> >> On Friday, March 3, 2023 at 8:06:17=C3=A2 =C2=AFAM UTC+11, John Larkin > >wrote: > >> >>> On Thu, 2 Mar 2023 09:07:43 -0800 (PST), whit3rd <whi...@gmail.com> > >> > >>>> wrote: > >> >>>> On Tuesday, February 28, 2023 at 7:05:59?AM UTC-8, 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 'much better leakage' relates to test protocols, more than reality. > >The recommendation to > >> >>>> use a 2N3904 as a reference goes back to National Semiconductor's (now > >TI) process for making those; > >> >>>> the Motorola (now ONsemi) process might be different (and breakdown is > >only specified as 'over 6.0V'). > >> >>>> > >> >>>> E-B breakdown also applies the opposite to 'normal' field on the surface > >of the > >> >>>> transistor, where the B and E contacts are made; such surfaces are passivated, > >but > >> >>>> field reversal can move dirt on the surface to age the component abnormally. > >> > >>>>> > >> >>>> So, no one knows 'how stable it is' for this usage, unless they've time/temperature > >> > >>>>> tested a few batches from a known process and the manufacturer doesn't > >change anything. > >> >>>> That '2N3904' part number was defined many decades ago, there have been > >lots > >> >>>> of variant parts holding to that loose specification, sold under that > >part number. > >> >>>> > >> >>>> It'll probably work. That doesn't mean it's good design practice to depend > >on it. > >> >>> > >> >>> You can get a 0.5% bandgap voltage reference for 4 cents. > >> >> > >> >> But John Larkin doesn't know the part number. H's probably thinking of > >the LM4040 > >> >> > >> >> > >> >> > >> >> https://www.ti.com/lit/ds/symlink/lm4040-n.pdf?HQS=3Ddis-mous-null-mousermode-dsf-pf-null-wwe&ts=3D1677716796343&ref_url=3Dhttps%253A%252F%252Fwww.mouser.jp%252F > >> > >>> > >> >> but that is lot more expensive than 4 cents - $1.37 even in thousands. > >> > >> > >> >6 cents: > >> > > >> >https://www.avnet.com/shop/us/products/diodes-inc/az431lantr-e1-3074457345625002718?CMP=3DEMA_FindChips_inventoryfeed_VSE > >> > >LM317 with adjust to ground is 1.2V bandgap > >> Or any other voltage you like up to 37 V > >> https://nl.aliexpress.com/item/32848278588.html > >> Almost for free > >> I always have some around. > > > >Not exactly precision references, but Jan Panteltje and John Larkin don't go in for precision. > > The advantage of LM317 is that you can use a trimpot or resistors to set it quite close to where you want it. > I often use 2 resistors in series, a big one and a smaller one for calibration.As if everybody else doesn't do the same thing. Putting the calibration resistor in parallel with the main resistor was called "select on test" where I worked in England, and was pretty popular. Customers fiddle with trim-pots - we had to put blobs of hot sealing wax on the adjustors so that our service engineers could see if the customers had been fiddling,> And it can deliver a LOT of current and has proven very reliable over the years and is still around since 1976 > https://en.wikipedia.org/wiki/LM317And I designed in a lot of them, but it isn't a precise voltage reference, and you really do need a second ground pin to let you set up a Kelvin connection, if you are setting up a serious reference voltage. -- Bill Sloman, Sydney
Reply by ●March 3, 20232023-03-03
On a sunny day (Fri, 3 Mar 2023 04:11:31 -0800 (PST)) it happened Anthony William Sloman <bill.sloman@ieee.org> wrote in <84e616ac-2578-4e1f-aab3-1d6303f1300fn@googlegroups.com>:>On Friday, March 3, 2023 at 10:35:48=E2=80=AFPM UTC+11, Jan Panteltje wrote: >> >On a sunny day (Fri, 3 Mar 2023 03:18:22 -0800 (PST)) it happened Anthony >> >William Sloman <bill....@ieee.org> wrote in >> <196fe320-7d36-4056...@googlegroups.com>: >> >On Friday, March 3, 2023 at 9:52:14=3DE2=3D80=3DAFPM UTC+11, Jan Panteltje >wrote: >> >> On a sunny day (Fri, 3 Mar 2023 11:01:43 +0100) it happened Klaus Vestergaard >> >>> >> >Kragelund <klau...@hotmail.com> wrote in <ttsgi6$jssm$1...@dont-email.me>: >> >>> >> >>On 02-03-2023 22:33, Anthony William Sloman wrote: >> >> >> On Friday, March 3, 2023 at 8:06:17=3DC3=3DA2 =3DC2=3DAFAM UTC+11, John >Larkin >> >wrote: >> >> >>> On Thu, 2 Mar 2023 09:07:43 -0800 (PST), whit3rd <whi...@gmail.com> >> >>> >> >>>> wrote: >> >> >>>> On Tuesday, February 28, 2023 at 7:05:59?AM UTC-8, 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 'much better leakage' relates to test protocols, more than reality. >> >>The recommendation to >> >> >>>> use a 2N3904 as a reference goes back to National Semiconductor's >(now >> >TI) process for making those; >> >> >>>> the Motorola (now ONsemi) process might be different (and breakdown >is >> >only specified as 'over 6.0V'). >> >> >>>> >> >> >>>> E-B breakdown also applies the opposite to 'normal' field on the surface >> >>of the >> >> >>>> transistor, where the B and E contacts are made; such surfaces are >passivated, >> >but >> >> >>>> field reversal can move dirt on the surface to age the component abnormally. >> >>> >> >>>>> >> >> >>>> So, no one knows 'how stable it is' for this usage, unless they've >time/temperature >> >> >> >>>>> tested a few batches from a known process and the manufacturer doesn't >> >>change anything. >> >> >>>> That '2N3904' part number was defined many decades ago, there have >been >> >lots >> >> >>>> of variant parts holding to that loose specification, sold under that >> >>part number. >> >> >>>> >> >> >>>> It'll probably work. That doesn't mean it's good design practice to >depend >> >on it. >> >> >>> >> >> >>> You can get a 0.5% bandgap voltage reference for 4 cents. >> >> >> >> >> >> But John Larkin doesn't know the part number. H's probably thinking >of >> >the LM4040 >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> https://www.ti.com/lit/ds/symlink/lm4040-n.pdf?HQS=3D3Ddis-mous-null-mousermode-dsf-pf-null-wwe&ts=3D3D1677716796343&ref_url=3D3Dhttps%253A%252F%252Fwww.mouser.jp%252F >> >>> >> >>> >> >> >> but that is lot more expensive than 4 cents - $1.37 even in thousands. >> >>> >> >> >> >> >6 cents: >> >> > >> >> >> >> >>https://www.avnet.com/shop/us/products/diodes-inc/az431lantr-e1-3074457345625002718?CMP=3D3DEMA_FindChips_inventoryfeed_VSE >> >>> >> >LM317 with adjust to ground is 1.2V bandgap >> >> Or any other voltage you like up to 37 V >> >> https://nl.aliexpress.com/item/32848278588.html >> >> Almost for free >> >> I always have some around. >> > >> >Not exactly precision references, but Jan Panteltje and John Larkin don't >go in for precision. >> >> The advantage of LM317 is that you can use a trimpot or resistors to set it >quite close to where you want it. >> I often use 2 resistors in series, a big one and a smaller one for calibration. > >As >if everybody else doesn't do the same thing. Putting the calibration resistor >in parallel with the main resistor was called "select on test" where >I worked in England, and was pretty popular. Customers fiddle with trim-pots >- we had to put blobs of hot sealing wax on the adjustors so that our service >engineers could see if the customers had been fiddling, > >> And it can deliver a LOT of current and has proven very reliable over the >years and is still around since 1976 >> https://en.wikipedia.org/wiki/LM317 > >And I designed in a lot of them, but it isn't a precise voltage reference, >and you really do need a second ground pin to let you set up a Kelvin connection, >if you are setting up a serious reference voltage.I also have some Microchip MCP1525 voltage reference, used it to 'calibrate' my Chinese multimeters its +-1%, about 90 cents 100 up, 52 weeks lead time on digikey. And TL431 pretty stable versus temperature, 100 pieces for 2 Euro 38 on aliexpress.... in stock... The Microchip PICs I use have a build in 1.024 V voltage reference,,,, 18F14K22 datasheet says: VR01 VFVR Fixed Voltage Reference min 0.984 nom 1.024 max 1.064 V Good enough for many projects, and comes free with the chip, in stock at severa places, else 24 weeks lead time digikey I think. Has build in 4 bit DAC multiplier for it, ADCs, hardware comparators. Many more things exist..
Reply by ●March 3, 20232023-03-03
>On Friday, March 3, 2023 at 10:35:48=E2=80=AFPM UTC+11, Jan Panteltje wrote:>The Microchip PICs I use have a build in 1.024 V voltage reference,,,, >18F14K22 datasheet says: VR01 VFVR Fixed Voltage Reference min 0.984 nom 1.024 max 1.064 V >Good enough for many projects, and comes free with the chip, in stock at severa places, else 24 weeks lead time digikey I think. >Has build in 4 bit DAC multiplier for it, ADCs, hardware comparators. >Many more things exist..PS when using the Microchip internal reference I usualy let it output its DAC voltage on a pin for test and measure it and then use a #define in the ASM for the precise value. So no trimpots needed to calibrate its ADCs. ; PIC Vref * 4 #define VREF D'4080' ; Measured
Reply by ●March 3, 20232023-03-03
On Fri, 03 Mar 2023 16:28:24 GMT, Jan Panteltje <alien@comet.invalid> wrote:>>On Friday, March 3, 2023 at 10:35:48=E2=80=AFPM UTC+11, Jan Panteltje wrote: > >>The Microchip PICs I use have a build in 1.024 V voltage reference,,,, >>18F14K22 datasheet says: VR01 VFVR Fixed Voltage Reference min 0.984 nom 1.024 max 1.064 V >>Good enough for many projects, and comes free with the chip, in stock at severa places, else 24 weeks lead time digikey I think. >>Has build in 4 bit DAC multiplier for it, ADCs, hardware comparators. >>Many more things exist.. > >PS >when using the Microchip internal reference I usualy let it output >its DAC voltage on a pin for test and measure it >and then use a #define in the ASM for the precise value. >So no trimpots needed to calibrate its ADCs. >; PIC Vref * 4 >#define VREF D'4080' ; Measured > > > > > >We usually have a BIST analog mux and ADC on a gadget, so we can scan all the power supplies and temperatures and such. That helps in production test as well as long-term in the field. The ADC is often free in a uP or an FPGA. We usually digitize ground and a good voltage reference as two mux channels, so we can live calibrate other channels based on those two points. We rarely use trimpots. Just for an occasional wideband gain trim, like in a GHz-class o/e converter or something.
Reply by ●March 3, 20232023-03-03
On 01/03/2023 14:54, Anthony William Sloman wrote:> There's a grab-bag National Semiconductor application note for the LM339 that tells much the same story on page 30. > > https://www.ti.com/lit/an/snoa654a/snoa654a.pdf > > "Experimental data has shown that any of National's process 21 transistors > which have been selected for low reverse beta (βR <.25) can be used quite satisfactorily as a zero T.C. > Zener. When connected as shown in Figure 37, the T.C. of the base-emitter Zener voltage is exactly > cancelled by the T.C. of the forward biased base-collector junction if biased at 1.5 mA. The diode can be > properly biased from any supply by adjusting RS to set lq equal to 1.5 mA." > > Process 21 was a gold-doped NPN fast switch - 2N2369 is the JEDEC nunber. >Using the C-B diode to temp compensate the E-B breakdown looks superficially neat but the devil is in the detail - they specify below unity reverse beta and that is vital. Otherwise once E-B breakdown occurs transistor action kicks in and you have a negistor or 4-layer diode kind of effect (imagine an SCR with zener gate to anode), conceptually like a uniploar low voltage diac. It is a hobbyists trick low parts count oscillator. piglet
Reply by ●March 3, 20232023-03-03
On 2023-03-03 15:35, piglet wrote:> On 01/03/2023 14:54, Anthony William Sloman wrote: >> There's a grab-bag National Semiconductor application note for the >> LM339 that tells much the same story on page 30. >> >> https://www.ti.com/lit/an/snoa654a/snoa654a.pdf >> >> "Experimental data has shown that any of National's process 21 >> transistors >> which have been selected for low reverse beta (βR <.25) can be used >> quite satisfactorily as a zero T.C. >> Zener. When connected as shown in Figure 37, the T.C. of the >> base-emitter Zener voltage is exactly >> cancelled by the T.C. of the forward biased base-collector junction if >> biased at 1.5 mA. The diode can be >> properly biased from any supply by adjusting RS to set lq equal to 1.5 >> mA." >> >> Process 21 was a gold-doped NPN fast switch - 2N2369 is the JEDEC nunber. >> > > Using the C-B diode to temp compensate the E-B breakdown looks > superficially neat but the devil is in the detail - they specify below > unity reverse beta and that is vital. Otherwise once E-B breakdown > occurs transistor action kicks in and you have a negistor or 4-layer > diode kind of effect (imagine an SCR with zener gate to anode), > conceptually like a uniploar low voltage diac. It is a hobbyists trick > low parts count oscillator. > > piglet > >Fun. I'll have to try that with a 2SD2704K (superbeta NPN with a lot of reverse beta and a spectacularly large BV_EBO). 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 ●March 4, 20232023-03-04
On Saturday, March 4, 2023 at 7:36:05 AM UTC+11, piglet wrote:> On 01/03/2023 14:54, Anthony William Sloman wrote: > > There's a grab-bag National Semiconductor application note for the LM339 that tells much the same story on page 30. > > > > https://www.ti.com/lit/an/snoa654a/snoa654a.pdf > > > > "Experimental data has shown that any of National's process 21 transistors > > which have been selected for low reverse beta (βR <.25) can be used quite satisfactorily as a zero T.C. > > Zener. When connected as shown in Figure 37, the T.C. of the base-emitter Zener voltage is exactly > > cancelled by the T.C. of the forward biased base-collector junction if biased at 1.5 mA. The diode can be > > properly biased from any supply by adjusting RS to set lq equal to 1.5 mA." > > > > Process 21 was a gold-doped NPN fast switch - 2N2369 is the JEDEC nunber. > > > Using the C-B diode to temp compensate the E-B breakdown looks > superficially neat but the devil is in the detail - they specify below > unity reverse beta and that is vital.It isn't being recommended for every part. The National Semiconductor application note was quite specific about what would work. Others have recommended the 2N3904 part which is process 23, a slight;ly bigger chip with a bit more interdigitation.> Otherwise once E-B breakdown > occurs transistor action kicks in and you have a negistor or 4-layer > diode kind of effect (imagine an SCR with zener gate to anode), > conceptually like a uniploar low voltage diac. It is a hobbyists trick > low parts count oscillator.You probably couldn't see that in LTSpice - all the transistor models are Gummel -Poon which doesn't model inverted gain all that accurately. LTSpice will run the more accurate VBIC model, but the parameters are commercial in confidence, and hobbyists can't get at them' -- Bill Sloman, Sydney
