John Larkin wrote:> On Sun, 15 Feb 2015 12:39:52 -0800 (PST), "M. Hamed" > <mhdpublic@gmail.com> wrote: > >> On Sunday, February 15, 2015 at 1:10:21 PM UTC-7, David Eather >> wrote: >>> So what? All standard zener diodes are used in reversed bias >>> mode >>> too. Go back to basics. >> >> I thought someone here or elsewhere mentioned that Zener >> effect is >> not necessarily the same as the avalanche effect in regular >> diodes. > > The physics is different, zener (quantum tunnelling) at low > voltages > and avalanche at high voltages, midway being around 5 volts > maybe. > > Most people and data sheets call all such diodes "zeners."Somewhat like "Xerox" for all photocopiers.
Chinese Germanium 1N34
Started by ●February 4, 2015
Reply by ●February 17, 20152015-02-17
Reply by ●February 17, 20152015-02-17
On Sunday, February 15, 2015 at 10:35:49 AM UTC-8, Michael Black wrote:> On Sun, 15 Feb 2015, David Eather wrote:> > ...by the way all diodes are zener diodes - we just don't normally > > run them in the breakdown region. > > Yes, all diodes can "zener" but they are reversed biased.A word of warning: don't test the reverse bias on point-contact, or light emitting, or low-noise photodiodes. Those devices have very sensitive near-surface regions that only stay clean if the electric field isn't given an unexpected polarity.> One surplus store here used to sell "zeners", some specific voltage, and > they were plastic encased transistors with a lead cut off.The base-emitter junction of a transistor is normally buried (far from the surface) so it is a useful and stable zener for many purposes. There are also diodes made in TO-92 cases, where 'extra' wires would be trimmed as a last step in manufacturing. I recall varactor and current-regulator diodes in such packages.
Reply by ●February 17, 20152015-02-17
On 2/17/2015 3:47 PM, whit3rd wrote:> On Sunday, February 15, 2015 at 10:35:49 AM UTC-8, Michael Black wrote: >> On Sun, 15 Feb 2015, David Eather wrote: > >>> ...by the way all diodes are zener diodes - we just don't normally >>> run them in the breakdown region. >> >> Yes, all diodes can "zener" but they are reversed biased. > > A word of warning: don't test the reverse bias on point-contact, > or light emitting, or low-noise photodiodes._Forward_ biasing some photodiodes can lead to tears, due to horrible current crowding at the contact. However, at least with Si, Ge, and InGaAs devices, reverse bias causes no worries right up to the rating. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●February 17, 20152015-02-17
On Tue, 17 Feb 2015 12:47:47 -0800 (PST), whit3rd <whit3rd@gmail.com> wrote:>On Sunday, February 15, 2015 at 10:35:49 AM UTC-8, Michael Black wrote: >> On Sun, 15 Feb 2015, David Eather wrote: > >> > ...by the way all diodes are zener diodes - we just don't normally >> > run them in the breakdown region. >> >> Yes, all diodes can "zener" but they are reversed biased. > >A word of warning: don't test the reverse bias on point-contact, >or light emitting, or low-noise photodiodes.Reverse biasing photodiodes is the usual way to use them. It reduces their capacitance and makes them a lot faster. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●February 18, 20152015-02-18
On Tue, 17 Feb 2015, Phil Hobbs wrote:> On 2/17/2015 3:47 PM, whit3rd wrote: >> On Sunday, February 15, 2015 at 10:35:49 AM UTC-8, Michael Black wrote: >>> On Sun, 15 Feb 2015, David Eather wrote: >> >>>> ...by the way all diodes are zener diodes - we just don't normally >>>> run them in the breakdown region. >>> >>> Yes, all diodes can "zener" but they are reversed biased. >> >> A word of warning: don't test the reverse bias on point-contact, >> or light emitting, or low-noise photodiodes. > > _Forward_ biasing some photodiodes can lead to tears, due to horrible current > crowding at the contact. However, at least with Si, Ge, and InGaAs devices, > reverse bias causes no worries right up to the rating. >Like I think I said earlier, the microwave diodes out of WWII like the 1N21 do not like to be tested, but I can't remember if that was merely because at the time a VOM would put too much current or voltage into it, or if the diodes are especially finicky. I remember saying something about a 1N21 to someone, and he said "you shouldn't have done that..." and I have seen (but can't remember techniques) for testing such diodes. LEDs can be reverse biased, but I gather they have relatively low reverse voltage rating, so you merely want to be careful. Michael
Reply by ●February 18, 20152015-02-18
whit3rd wrote:> On Sunday, February 15, 2015 at 10:35:49 AM UTC-8, Michael > Black > wrote: >> On Sun, 15 Feb 2015, David Eather wrote: > >>> ...by the way all diodes are zener diodes - we just don't >>> normally >>> run them in the breakdown region. >> >> Yes, all diodes can "zener" but they are reversed biased. > > A word of warning: don't test the reverse bias on > point-contact, > or light emitting, or low-noise photodiodes. Those devices > have > very sensitive near-surface regions that only stay clean if the > electric field isn't given an unexpected polarity. >I've seen LEDs in cheap Chinese and Indian products run directly from 230VAC with a single series resistor and nothing else. That obviously places the LED in reverse breakdown every half cycle. I haven't paid enough attention to see if/how their performance changes with time.
Reply by ●February 18, 20152015-02-18
On Tuesday, February 17, 2015 at 10:51:44 PM UTC-5, John Larkin wrote:> On Tue, 17 Feb 2015 12:47:47 -0800 (PST), whit3rd <whit3rd@gmail.com> > wrote: > > >On Sunday, February 15, 2015 at 10:35:49 AM UTC-8, Michael Black wrote: > >> On Sun, 15 Feb 2015, David Eather wrote: > > > >> > ...by the way all diodes are zener diodes - we just don't normally > >> > run them in the breakdown region. > >> > >> Yes, all diodes can "zener" but they are reversed biased. > > > >A word of warning: don't test the reverse bias on point-contact, > >or light emitting, or low-noise photodiodes. > > Reverse biasing photodiodes is the usual way to use them. It reduces > their capacitance and makes them a lot faster.Anyone tried taking a garden variety photodiode up to the point where it starts avalanching? (Maybe in a dark room... there are some thing better done with the lights off :^) George H.> > > -- > > John Larkin Highland Technology, Inc > picosecond timing laser drivers and controllers > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
Reply by ●February 18, 20152015-02-18
On Wednesday, February 18, 2015 at 1:25:53 AM UTC-5, Pimpom wrote:> whit3rd wrote: > > On Sunday, February 15, 2015 at 10:35:49 AM UTC-8, Michael > > Black > > wrote: > >> On Sun, 15 Feb 2015, David Eather wrote: > > > >>> ...by the way all diodes are zener diodes - we just don't > >>> normally > >>> run them in the breakdown region. > >> > >> Yes, all diodes can "zener" but they are reversed biased. > > > > A word of warning: don't test the reverse bias on > > point-contact, > > or light emitting, or low-noise photodiodes. Those devices > > have > > very sensitive near-surface regions that only stay clean if the > > electric field isn't given an unexpected polarity. > > > I've seen LEDs in cheap Chinese and Indian products run directly > from 230VAC with a single series resistor and nothing else. That > obviously places the LED in reverse breakdown every half cycle. I > haven't paid enough attention to see if/how their performance > changes with time.I reversed biased several LEDs.. most were good up to ~100V or so.. 230VAC seems like a lot... but maybe with the "right" led. George H.
Reply by ●February 18, 20152015-02-18
George Herold wrote:> On Wednesday, February 18, 2015 at 1:25:53 AM UTC-5, Pimpom > wrote: >> whit3rd wrote: >>> >>> A word of warning: don't test the reverse bias on >>> point-contact, >>> or light emitting, or low-noise photodiodes. Those devices >>> have >>> very sensitive near-surface regions that only stay clean if >>> the >>> electric field isn't given an unexpected polarity. >>> >> I've seen LEDs in cheap Chinese and Indian products run >> directly >> from 230VAC with a single series resistor and nothing else. >> That >> obviously places the LED in reverse breakdown every half >> cycle. I >> haven't paid enough attention to see if/how their performance >> changes with time. > > I reversed biased several LEDs.. most were good up to ~100V or > so.. > 230VAC seems like a lot... but maybe with the "right" led. >I see now how my post could be incorrectly interpreted. I mean a *single* LED used as a power indicator, not a string of them, and without any other component shunting it to prevent reverse operation. The series resistor limits the current in both forward and reverse breakdown mode. Usually these are run at a mA or two. The preceding post by whit3rd made me wonder if LEDs used like this suffer significant degradation in light ouput or lifespan.
Reply by ●February 18, 20152015-02-18
On Wed, 18 Feb 2015 06:17:28 -0800 (PST), George Herold <gherold@teachspin.com> wrote:>On Tuesday, February 17, 2015 at 10:51:44 PM UTC-5, John Larkin wrote: >> On Tue, 17 Feb 2015 12:47:47 -0800 (PST), whit3rd <whit3rd@gmail.com> >> wrote: >> >> >On Sunday, February 15, 2015 at 10:35:49 AM UTC-8, Michael Black wrote: >> >> On Sun, 15 Feb 2015, David Eather wrote: >> > >> >> > ...by the way all diodes are zener diodes - we just don't normally >> >> > run them in the breakdown region. >> >> >> >> Yes, all diodes can "zener" but they are reversed biased. >> > >> >A word of warning: don't test the reverse bias on point-contact, >> >or light emitting, or low-noise photodiodes. >> >> Reverse biasing photodiodes is the usual way to use them. It reduces >> their capacitance and makes them a lot faster. > >Anyone tried taking a garden variety photodiode up to the point >where it starts avalanching? >(Maybe in a dark room... there are some thing better done with the >lights off :^) >No, but that's what an APD does (probably with special doping) -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
