On Sun, 10 May 2015 12:14:22 -0700, John Larkin
<jlarkin@highlandtechnology.com> wrote:
>On Sun, 10 May 2015 06:18:04 +0000 (UTC), mroberds@att.net wrote:
>
>>John Larkin <jlarkin@highlandtechnology.com> wrote:
>>> On Sun, 10 May 2015 04:46:51 +0000 (UTC), mroberds@att.net wrote:
>>>> John Larkin <jlarkin@highlandtechnology.com> wrote:
>>>>
>>>>> It's probably OK at 15, since I don't expect anybody to stall it,
>>>>> but it's weird. We'll get some 24 volt versions to test.
>>>>
>>>> Toss in a couple of 1N4001s (or surface-mount equal) in series with
>>>> the fan connector and get on down the road.
>>>
>>> But the original board, rev A, first try, works with no kluges.
>>> Hacking it would be a sin.
>>
>>I think that about my code when all the modules are still sitting around
>>version 0.x. Usually, by the time it ships, some modules are up to 1.5
>>or more. The beauty is still there, but you have to look past the cruft
>>to see it.
>
>Code can be, and often is, edited and recompiled scores, maybe
>hundreds of times, before people decide that it's good enough, or that
>it has to ship. Code doesn't have pads that fall off after a dozen
>reworks. A PC board can't be edited and re-etched in 10 minutes;
>iterations take more like a month, and are messy and expensive and
>publically embarassing. Electronic design has to be done right, and
>brutally checked, at the engineering level, before the Gerbers are
>formally released and boards ordered and assembled and tested.
>
>In general, the easier it is to change something, the less care will
>go into its design, and the more it will get changed. And the more
>bugs will never get fixed.
>
>
>>
>>Stick the diodes in the fan harness?
>
>We could, a 3 volt zener or a resistor in a bit of shrink tubing. Or
>just run a 12 volt fan at 15 volts! That looks like it will work.
>
>Our FPGA surface temp is over 100C, and the box quits working at 80 to
>85C ambient. We could sell that, but we'd prefer a little more margin.
>
>That red uZed board has a couple of holes for mounting a tiny fan
>above the FPGA. We may do that, as opposed to trying to cool the
>entire box.
This rig lets us run up to 90C ambient. The guy who tested it wimped
out there; I'd have cranked up the temp until something failed.
https://dl.dropboxusercontent.com/u/53724080/Thermal/FPGA_Fan.JPG
There is an on-chip temp sensor in the ZYNQ, but we'd need an FPGA
compile and some ARM code to access it, which isn't in the budget just
now. Maybe next iteration.
--
John Larkin Highland Technology, Inc
picosecond timing precision measurement
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Reply by John Larkin●May 10, 20152015-05-10
On Sun, 10 May 2015 06:18:04 +0000 (UTC), mroberds@att.net wrote:
>John Larkin <jlarkin@highlandtechnology.com> wrote:
>> On Sun, 10 May 2015 04:46:51 +0000 (UTC), mroberds@att.net wrote:
>>> John Larkin <jlarkin@highlandtechnology.com> wrote:
>>>
>>>> It's probably OK at 15, since I don't expect anybody to stall it,
>>>> but it's weird. We'll get some 24 volt versions to test.
>>>
>>> Toss in a couple of 1N4001s (or surface-mount equal) in series with
>>> the fan connector and get on down the road.
>>
>> But the original board, rev A, first try, works with no kluges.
>> Hacking it would be a sin.
>
>I think that about my code when all the modules are still sitting around
>version 0.x. Usually, by the time it ships, some modules are up to 1.5
>or more. The beauty is still there, but you have to look past the cruft
>to see it.
Code can be, and often is, edited and recompiled scores, maybe
hundreds of times, before people decide that it's good enough, or that
it has to ship. Code doesn't have pads that fall off after a dozen
reworks. A PC board can't be edited and re-etched in 10 minutes;
iterations take more like a month, and are messy and expensive and
publically embarassing. Electronic design has to be done right, and
brutally checked, at the engineering level, before the Gerbers are
formally released and boards ordered and assembled and tested.
In general, the easier it is to change something, the less care will
go into its design, and the more it will get changed. And the more
bugs will never get fixed.
>
>Stick the diodes in the fan harness?
We could, a 3 volt zener or a resistor in a bit of shrink tubing. Or
just run a 12 volt fan at 15 volts! That looks like it will work.
Our FPGA surface temp is over 100C, and the box quits working at 80 to
85C ambient. We could sell that, but we'd prefer a little more margin.
That red uZed board has a couple of holes for mounting a tiny fan
above the FPGA. We may do that, as opposed to trying to cool the
entire box.
--
John Larkin Highland Technology, Inc
picosecond timing laser drivers and controllers
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Reply by John Larkin●May 10, 20152015-05-10
On Sun, 10 May 2015 13:02:04 -0400, Phil Hobbs
<hobbs@electrooptical.net> wrote:
>On 5/10/2015 1:19 AM, John Larkin wrote:
>> On Sun, 10 May 2015 04:46:51 +0000 (UTC), mroberds@att.net wrote:
>>
>>> John Larkin <jlarkin@highlandtechnology.com> wrote:
>>>> It's probably OK at 15, since I don't expect anybody to stall it, but
>>>> it's weird. We'll get some 24 volt versions to test.
>>>
>>> Toss in a couple of 1N4001s (or surface-mount equal) in series with the
>>> fan connector and get on down the road.
>>
>> But the original board, rev A, first try, works with no kluges.
>> Hacking it would be a sin.
>>
>> https://dl.dropboxusercontent.com/u/53724080/PCBs/P350_SN1.JPG
>
>Couldn't you get Avnet to change their colour scheme? It clashes
>horribly. ;)
>
>Cheers
>
>Phil Hobbs
Think so? I kind of like it. But then, I have a red car and I'm typing
in a red t-shirt.
--
John Larkin Highland Technology, Inc
picosecond timing laser drivers and controllers
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Reply by Phil Hobbs●May 10, 20152015-05-10
On 5/10/2015 1:19 AM, John Larkin wrote:
> On Sun, 10 May 2015 04:46:51 +0000 (UTC), mroberds@att.net wrote:
>
>> John Larkin <jlarkin@highlandtechnology.com> wrote:
>>> It's probably OK at 15, since I don't expect anybody to stall it, but
>>> it's weird. We'll get some 24 volt versions to test.
>>
>> Toss in a couple of 1N4001s (or surface-mount equal) in series with the
>> fan connector and get on down the road.
>
> But the original board, rev A, first try, works with no kluges.
> Hacking it would be a sin.
>
> https://dl.dropboxusercontent.com/u/53724080/PCBs/P350_SN1.JPG
Couldn't you get Avnet to change their colour scheme? It clashes
horribly. ;)
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 ●May 10, 20152015-05-10
John Larkin <jlarkin@highlandtechnology.com> wrote:
> On Sun, 10 May 2015 04:46:51 +0000 (UTC), mroberds@att.net wrote:
>> John Larkin <jlarkin@highlandtechnology.com> wrote:
>>
>>> It's probably OK at 15, since I don't expect anybody to stall it,
>>> but it's weird. We'll get some 24 volt versions to test.
>>
>> Toss in a couple of 1N4001s (or surface-mount equal) in series with
>> the fan connector and get on down the road.
>
> But the original board, rev A, first try, works with no kluges.
> Hacking it would be a sin.
I think that about my code when all the modules are still sitting around
version 0.x. Usually, by the time it ships, some modules are up to 1.5
or more. The beauty is still there, but you have to look past the cruft
to see it.
Stick the diodes in the fan harness?
Matt Roberds
Reply by John Larkin●May 10, 20152015-05-10
On Sun, 10 May 2015 04:46:51 +0000 (UTC), mroberds@att.net wrote:
>John Larkin <jlarkin@highlandtechnology.com> wrote:
>> It's probably OK at 15, since I don't expect anybody to stall it, but
>> it's weird. We'll get some 24 volt versions to test.
>
>Toss in a couple of 1N4001s (or surface-mount equal) in series with the
>fan connector and get on down the road.
John Larkin <jlarkin@highlandtechnology.com> wrote:
> It's probably OK at 15, since I don't expect anybody to stall it, but
> it's weird. We'll get some 24 volt versions to test.
Toss in a couple of 1N4001s (or surface-mount equal) in series with the
fan connector and get on down the road.
Yes, I usually write software for a living... why are you looking at me
funny?
> Seems like half my hassles lately are thermal.
Pic somewhat related: https://xkcd.com/451/ , especially the first
panel.
Matt Roberds
Reply by Phil Hobbs●May 9, 20152015-05-09
On 5/8/2015 7:45 PM, Bill Bowden wrote:
> "DecadentLinuxUserNumeroUno" <DLU1@DecadentLinuxUser.org> wrote in message
> news:14jnkal3sg1hncthrdmnn9q8kvqonfpf42@4ax.com...
>> On Sat, 2 May 2015 19:45:51 -0700, "Bill Bowden"
>> <bperryb@bowdenshobbycircuits.info> Gave us:
>>
>>> Is it safe to operate a 2N3904 in a switching application with a supply
>>> voltage of 48 volts? The data sheet says Vceo is 40 and Vcbo is 60 volts.
>>> When the transistor switches off, the collector to emitter voltage will be
>>> 48 and the base voltage will be near 0 through a resistor. Any problems
>>> with
>>> that?
>>>
>>
>> Absolutely presents a problem...
>>
>> This will let the smoke out. No question.
>
> I thought the specs indicated "guaranteed" performance? Vceo of 40 would
> imply every device would meet that spec plus a little more? It's a resistive
> load, so there aren't any inductive considerations. And the base will be
> grounded to the emitter through a 3K resistor when the collector voltage is
> 48.
The collector-base leakage rises steeply with V_CB. With the base left
open, it gets multiplied by beta, so I_C goes through the roof at a
lower voltage. If you prevent the B-E junction from getting
forward-biased, e.g. by shorting B-E, it holds up out to V_CES, which is
higher. A resistor isn't quite as good, and reverse bias is a bit
better, so you have a family of breakdown voltages rather than just one.
V_CEO < V_CER < V_CES < V_CEX .
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 jfen...@my-deja.com●May 9, 20152015-05-09
On Friday, May 8, 2015 at 4:45:53 PM UTC-7, Bill Bowden wrote:
> I thought the specs indicated "guaranteed" performance? Vceo
> of 40 would imply every device would meet that spec plus a
> little more?
I would expect the answer to this question would depend on the date code. A part from the 1980s made by diffusion would probably have a very wide range of propeerties, both within a lot and lot-to-lot. Something made in the 21st century by ion implantation might have a very tight range, and could be manufactured with very little "safety margin".
Why do you raise the question? Is it academic curiosity, or do you havee a specific application and lots of 2N3904s in the warehouse? The 2N3904 is cheap (about 10 cents is smalll hobbyist quantities), so a part with a sufficiently higher BV is probably less than 20 cents in large manufacturing quantities. You would have to sell a lot of widgets to recover the additional engineering cost of using an underspec'd part.
Reply by Bill Bowden●May 8, 20152015-05-08
"DecadentLinuxUserNumeroUno" <DLU1@DecadentLinuxUser.org> wrote in message
news:14jnkal3sg1hncthrdmnn9q8kvqonfpf42@4ax.com...
> On Sat, 2 May 2015 19:45:51 -0700, "Bill Bowden"
> <bperryb@bowdenshobbycircuits.info> Gave us:
>
>>Is it safe to operate a 2N3904 in a switching application with a supply
>>voltage of 48 volts? The data sheet says Vceo is 40 and Vcbo is 60 volts.
>>When the transistor switches off, the collector to emitter voltage will be
>>48 and the base voltage will be near 0 through a resistor. Any problems
>>with
>>that?
>>
>
> Absolutely presents a problem...
>
> This will let the smoke out. No question.
I thought the specs indicated "guaranteed" performance? Vceo of 40 would
imply every device would meet that spec plus a little more? It's a resistive
load, so there aren't any inductive considerations. And the base will be
grounded to the emitter through a 3K resistor when the collector voltage is
48.
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