Avalanche Transistor and Boost to 100V - Page 1
Forum section: electronics / beginners

author: MAntunes
author_rank: Regular Contributor
timestamp: August 01, 2016, 08:38:47 pm
content: Hello,I have a project in hands in which I need to explore the avalanche breakdown of a transistor.Do you know of any common transistor besides the 2N2369A and the 2N3904 that verify this fenomenon?To reach the breakdown of the transistor I need very high voltages >70V. I think I'll use a switching converter (boost), do you know of any IC that can reach this voltages? Ideally >100V.Regard,Miguel

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 01, 2016, 09:20:42 pm
content: Miguel,Check this thread:https://www.eevblog.com/forum/projects/transmission-line-avalanche-pulse-generator/msg185639/#msg185639I use a BFR505 which will avalanche at around 35V.and this thread:https://www.eevblog.com/forum/blog/eevblog-306-jim-williams-pulse-generator/This uses the 2N2369A. It is based on Linear Technology application note AN47:Link:http://cds.linear.com/docs/en/application-note/an47fa.pdfappendix D starts on page 93.Some 2n3904 will avalanche but it takes higher voltage.Regards,Jay_Diddy_B

author: gdewitte
author_rank: Unknown
timestamp: August 01, 2016, 09:25:57 pm
content: AN47 also uses a LT1073 to generate ~90V from a 1.5V battery, so you can build a nice compact unit.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 02, 2016, 12:03:40 am
content: It is my experience that most transistors exhibit latching avalanche behavior. They may not be very fast, or very high current, or deliver strong latching action over a useful range of bias currents. Finding ones that do, requires lots of testing.In the extreme, I've avalanched horizontal output transistors (2SC5404 and etc.) at 1800V, but the bias range is narrow, and when they do fire, they fire once and that's it.Probably, large junctions do not avalanche evenly, causing localized damage. Smaller transistors are better. To deliver large amounts of current, you need to use many small transistors, synchronized with a trigger pulse, and connected in parallel with a power combiner network.Tim

author: David Hess
author_rank: Super Contributor
timestamp: August 02, 2016, 01:40:10 am
content: Quote from: T3sl4co1l on August 02, 2016, 12:03:40 amThis reminds me of the times when component failure mode was "disappearance".Transistors specified for avalanche applications have a chart for current versus pulse width versus number of operations to failure. The lowest chart I have seen only extends down to 1000 operations to failure.Your story also reminds me of the one about the incoming quality control guy who was testing transistors for emitter-base breakdown voltage and pronouncing them all good.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 02, 2016, 01:42:18 am
content: Heh, it would take a lot of avalanche energy to disappear a HOT, though.I think what happens is, a small part of the junction gets "disappeared". Afterwards, it never really turns off -- I've measured 10-100kohms (DCR) across C-E. It still seems to work as normal, except for the huge leakage.Tim

author: David Hess
author_rank: Super Contributor
timestamp: August 02, 2016, 04:24:26 am
content: I would hope so but I have seen, or rather not seen, plastic packaged TO-220 transistors vanish leaving behind either the leads or tab if it was mounted to a heat sink. Somewhere I have an Arco Mills drawer filled with TO-220 MOSFETs demonstrating the various disassembly modes when you exceed thermal limits.I think you are right about the failure mode. Above a certain energy, the thermal capacitance at any hot spot is not high enough to prevent damage do to high temperature and that area turns into a puddle of impure silicon.

author: CJay
author_rank: Super Contributor
timestamp: August 02, 2016, 06:00:41 am
content: Quote from: David Hess on August 02, 2016, 04:24:26 amI had a few IRFP450 TO-3P MOSFETs that demonstrated explosive spot welding, nothing left of them but the drain lead and the heatsink tabs were perforated with a neat hole wher ethemolten ejecta had drilled through the attached heatsink as well necessitating percussive removal of the remains.

author: David Hess
author_rank: Super Contributor
timestamp: August 02, 2016, 10:53:17 pm
content: Quote from: CJay on August 02, 2016, 06:00:41 amThese days I try to settle for blowing or melting the bond wires off on TO-3 packages.

author: Gyro
author_rank: Super Contributor
timestamp: August 03, 2016, 09:08:02 am
content: It's still a mystery to me how they manage to successfully weld bond wiresthat thickonto the die metallization.

author: nfmax
author_rank: Super Contributor
timestamp: August 03, 2016, 09:48:34 am
content: We have used FMMT415TD devices in avalanche laser driver applications with success

author: SeanB
author_rank: Super Contributor
timestamp: August 03, 2016, 11:18:17 am
content: Quote from: Gyro on August 03, 2016, 09:08:02 amEasy, you keep the roll of aluminium wire in an oxygen free atmosphere from drawing, so there is only a very thin oxide layer, and then simply ultrasonically weld this to the clean die. that way the soft metal deforms easily, and bonds well with the die top metal, with not much oxide layer obstructing the weld. The wire then will form a thicker oxide layer on it's own with the heat from the seam welding of the can.

author: Gyro
author_rank: Super Contributor
timestamp: August 03, 2016, 11:58:49 am
content: Sure, I understand how it's done Sean, It's more the huge disparity between the thickness (and mass) of the wire against the thickness of the metallization. I suppose there is a decent contact patch area but it just feels as if the wire would rub out the metallization during ultrasonic welding or 'rip' it off. At the end of the day I guess it is just Aluminium to Aluminium.

author: David Hess
author_rank: Super Contributor
timestamp: August 03, 2016, 05:58:57 pm
content: RF transistors and other high performance or high reliability parts do the same thing using gold metalization and gold wire which should be a lot easier since an inert atmosphere will not be needed. That might be the way to go for amateur hybrid construction assuming you could get all of the parts you needed with gold metalization. Note that gold itself requires a barrier metal when used with silicon because otherwise it will diffuse into the junctions and act as a dopant.How quickly does the aluminum oxide form? Is an inert atmosphere required during the time when you access the device, draw the wire, and bond it? I guess it would be no big deal to have a nitrogen jet displacing air near the bonding head and you can get soldering irons now which do this very thing using their own nitrogen generator.

author: SeanB
author_rank: Super Contributor
timestamp: August 03, 2016, 07:40:12 pm
content: It forms in seconds, so you need a CA setup all the way till after the bonding and even till the hermetic sealing, so there is no moisture trapped inside the housing to cause issues with reliability down the line. On the die you can coat with Parylene before scribing, so the bond wire just has to displace a small amount to get to bare oxide free metal for the bonding.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 03, 2016, 07:57:26 pm
content: Inert isn't necessary. Friction of the ultrasonic or wedge bonding process ensures clean faces, just as contact wiping in switches and connectors ensures a good contact.Tim